boiling water experiment results

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Salt and the boiling temperature of water

Introduction: (initial observation).

At home hot water is used for cooking and heating systems such as hot water radiators. In laboratories hot water is used in water baths. Hot water has many industrial applications as well.

One problem with water is that it never gets hotter than 100º Celsius. Any additional heat will only cause more evaporation. Being able to control or modify the boiling point of water may be helpful for any applications requiring heat transfer.

In this project you will study the effect of table salt on the boiling temperature of water. Report your results in a table and draw a graph to visually display your results.

If you have any questions, click on the “Ask Question” button at the top of this page to send me your questions. I may respond by email, but often I update this page with the information that you need.

You will also need to know:

• How to select a project?
• What are variables (Dependent, Independent, Control)?
• What is a control experiment?
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• What is an abstract? How to write it?
• Samples of display boards   
• How to write a report?

Project Advisor

Information Gathering:

Find out about boiling and boiling point point. Read books, magazines or ask professionals who might know in order to learn about the effect of salt on the boiling point of water. Keep track of where you got your information from.

matter : anything that occupies space and has mass.

mass : the quantity of matter contained by an object. Mass is measured in terms of the force required to change the speed or direction of its movement.

liquid : the state in which matter takes the shape of its container, assumes a horizontal upper surface, and has a fairly definite volume.

boiling point : the temperature at which the vapor pressure of a liquid equals the pressure of the gas above it.

temperature : measure of the hotness or coldness of a body.

pressure : force exerted on a unit area. The SI unit of pressure is the Pascal (Pa).

gas : the state in which matter has neither definite volume nor shape.

boiling -point elevation: the elevation of the boiling point of a liquid by addition of a solute.

Effect of air pressure

A liquid boils when its vapor pressure becomes equal to atmospheric pressure. Low atmospheric pressure causes the boiling point to go down; high pressure drives it up. Atmospheric pressure varies a bit from day to day, depending on the weather, and it varies from place to place, depending on the altitude.

Other related links:

• Boiling Point
• Boiling point elevation
• Boiling temperature of water solutions

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to determine the effect of salt on the boiling point of water.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

• The independent variable (also known as manipulated variable) is the amount of salt.
• Dependent variable (also known as responding variable) is the boiling point of water.
• Controlled variables are the air temperature and pressure. Perform all your experiments in the same day while the air pressure and temperature will not be subject to noticeable changes.

Hypothesis:

Based on your gathered information, make an educated guess about the effect of salt on boiling point of water.

Following are two sample hypothesis:

Sample hypothesis 1:

I hypothesize that salt will reduce the boiling point of water. My hypothesis is based on my information that salt reduce the freezing point of water and it is used as an anti freeze in winter.

Sample hypothesis 2:

I hypothesize that salt will increase the boiling point of water. My hypothesis is based on my information that salt does not boil as easy as water, so when mixed with water it may make it hard for water to boil as well.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Introduction : In this experiment you will test the effect of table salt (sodium chloride) on the boiling point of water. You may repeat this experiment with other solutes such as sugar, Epsom salt (Magnesium sulfate) and Salt cake (Sodium sulfate). Experiment involve preparing salt-water solutions with different amounts of salt; heat them to the boiling temperature and then measure and record the temperature while the solution is boiling.

• Fill up a glass beaker or a small pot with 100 ml distilled water.
• Place a thermometer in the water several centimeters from the bottom of the pot. Make sure you are using a thermometer with at least one degree markings to insure accurate measurements.
• Begin to heat the water. Take temperature readings every 10 seconds.
• Continue reading the temperature until it remains constant for at least four measurements. This is the boiling point.
• Repeat the steps 1 to 4; however, each time add a different amount of salt to the water. Suggested amounts of salt are 5, 10, 15, 20 and 25 grams as shown in the following table.

Your results table may look like this:

• Use tap water or drinking water if you don’t have access to the distilled water
• If your pot or beaker are big and you need to do your experiment with more water, increase the amount of salt at the same ratio.
• C = Celsius Temperature Scale (Centigrade)
• F = Fahrenheit
• If you don’t have a scale to weight 5 grams salt, use one small tea spoon. That will hold approximately 5 grams of salt.
• The first experiment with pure water is also the control for your other experiments.
• 102ºC and 106ºC in the above table are possible answers reported by other students. Please note that they may be wrong or inaccurate!

Make a bar graph:

For each of the six solutions that you test make a vertical bar (so your graph will have 6 vertical bars). The height of each bar will represent the boiling temperature of one specific solution. The name of the bar will be the amount of salt added.

The bar graph in the right is for a similar experiment with only 3 different solutions. 0 is for no salt, 1 is for 1 table spoon and 2 is for 2 table spoon salt in one quart of water.

Materials and Equipment:

• Thermometer* (available at science suppliers),
• Glass beakers or metal pots,
• Electric stove (hotplate)

* Glass and dial thermometers shown above are available at MiniScience.com and klk.com. Either of the two models may be used for freezing temperatures. Dial thermometers last longer; however, glass thermometers are more accurate.

Results of Experiment (Observation):

The above table will be completed and used as the result of your experiment. You may also write in a paragraph or two the result. What you write may be an answer to the following questions:

1. What was the highest temperature that the salt water reached?

2. At what temperature does the pure water boil?

If the thermometer extends beyond the outside of the pot it reads a higher temperature. Heat from the stove burner makes the thermometer read higher. Keep the thermometer over the pot when making temperature measurements.

Calculations:

No calculation is required

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to describe the effect of salt on freezing point of water. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books about salt, water, general chemistry, physical chemistry or chemical physics. Look for chapters that discuss changes in physical properties of a substance when mixed with other substances.

List the books and the online resources that you use in this part of your report.

It is always important for students, parents and teachers to know a good source for science related equipment and supplies they need for their science activities. Please note that many online stores for science supplies are managed by MiniScience.

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What will happen if we add salt to boiling water?

I would like to have a good understanding of what is happening when you add salt to boiling water.

My understanding is that the boiling point will be higher, thus lengthening the process (obtaining boiling water), but at the same time, the dissolved salt reduce the polarization effect of the water molecules on the heat capacity, thus shortening the process.

Is this competition between these two effects real ? Is it something else ?

• thermodynamics
• physical-chemistry
• applied-physics

• 2 $\begingroup$ Perhaps a perfect example of a physics/chemistry crossover question that we should allow. $\endgroup$ –  Nick Commented Nov 3, 2010 at 16:31
• $\begingroup$ We did this this in first-semester chemistry. I'll try to come back when I have opportunity. $\endgroup$ –  Mark C Commented Nov 7, 2010 at 3:56

4 Answers 4

Okay, first we have the phenomenon: Yes. adding salt increases the boiling point of water, which means that you have to input more energy to get the water to boil, but your egg or pasta will cook faster once you do, because the water will be hotter.

Then there's the why. The boiling point of a liquid is the temperature at which the vapor pressure of the liquid is the same as the atmospheric pressure above the liquid. If we can artificially increase the vapor pressure of the liquid, we decrease the boiling temperature. If we can artificially decrease the vapor pressure of the liquid, we increase the boiling temperature. So the question has now become: why does the vapor pressure of water decrease when we add salt to it?

So imagine a pot of water. At any given temperature there will be some water molecules in the gas phase above the pot (that's the origin of the vapor pressure), and some in the liquid phase in the pot. The proportion in the two phases is determined by the interplay of lowering potential energy (by decreasing elevation in gravity, by forming hydrogen bonds, by lining up the polar ends of the molecules, etc.) and increasing the entropy (there's more accessible states in the gas phase, most liquids are incompressible, etc.). The potential energy part favors the liquid phase, while the entropy part favors the gas phase. The real requirement here is to minimize the free energy, F = U - TS, with F the free energy, U the potential, T the temperature, and S the entropy. Since S is paired with the temperature, increasing the temperature increases the impact of the entropy part, which is why the vapor pressure increases as we increase the temperature.

So now we toss in some salt, while keeping the temperature fixed. The volume fraction of the water decreases, and suddenly there are new accessible states for the water molecules in the liquid phase -- so the vapor pressure decreases. We keep adding salt and the vapor pressure keeps decreasing. If we keep going, eventually there's no vapor pressure.

Raoult's law says that the vapor pressure of a solution is proportional to the vapor pressure of the pure solvent (basically that there is a straight line between the pure vapor pressure and zero, when we've buried it in salt). That's taken as the definition of an ideal solution. Real solutions have a curved functional form between the two boundary conditions, with the deviations from linearity coming from interactions between the solute (the salt) and the solvent (the water). Those interactions might be things like breaking up the network of hydrogen bonds in the water, disrupting the polarization arrangement (both of which will favor gas phase), or bonding/pairing up with water molecules (which will favor liquid phase). At relatively low concentrations of solute the interaction effects are pretty small, so the dependence of vapor pressure on solute concentration remains roughly linear. The cool observation though is that at most temperatures and for most solvents, it doesn't matter what solute you use (as long as the solute itself doesn't have a vapor pressure), the vapor pressure of the solvent is still decreased by adding solute (which indicates that the entropic contribution is the most important part, and the interactions don't play a big role).

Now to sum up: for a given concentration of salt dissolved in water, there are more states accessible to the water molecules in the liquid phase than there are in pure water. So at every water temperature as we pour in energy to make it boil, there will be a lower vapor pressure than there would have been without the salt, and thus we won't get to the boiling point until the water has reached a higher temperature (until we've poured in more energy than we would have had to). Salt does disrupt the network of hydrogen bonds in the water molecules, but the effect isn't very big at reasonable concentrations of salt, and it's never big enough to counteract the entropic effect.

good theory

how about a test

my niece just did 3 trials each on 2 cups of water and varied the number of tablespoons of salt

0 and 1 tablespoons boiled at about 10.5 minutes 2 tablespoons boiled at about 9.3 minutes 3 about 7.5 minutes and 4 boiled at about 6 minutes.

and now she wants to know why she got those results

• $\begingroup$ Nice experiment--- this is a shocking property of salt in water. $\endgroup$ –  Ron Maimon Commented Jul 15, 2012 at 5:54

The competition is real, and it's no contest. The reduction in specific heat from the polar effect swamps the miniscule elevation of the boiling point.

When you dissolve salt in water, it makes ions in solution, and the ionic atoms trap a cage of water around them immobile. The net effect is that you reduce the number of degrees of freedom, and you reduce the specific heat. So a given amount of heat energy is more effective at heating salt water than ordinary water. The effect is large, see kwinb's answer for a qualitative experiment.

This means that when you add salt to boiling water, the act of dissolving the salt (which keeps the internal energy fixed, or releases internal energy), is more than enough to heat the water to the new boiling temperature. I have often added salt to boiling water, and I used to expect it to stop boiling momentarily, to catch up to the new boiling point. Instead, I consistently noticed hyper-boiling where I added the salt, and no time-lag. The reason is the heat released as the salt is dissolved.

• 2 $\begingroup$ Just a thought - if you're adding salt to boiling water, the crystals will be providing nucleation centres before they dissolve. I doubt this is the main cause of the increased boiling you see, though. $\endgroup$ –  Benjamin Hodgson Commented Sep 24, 2012 at 10:44
• $\begingroup$ Yup, you are just adding nucleation sites. Try it with sand. The same thing will occur. To test it, you must add the salt well below the boiling point. $\endgroup$ –  abalter Commented Jun 22, 2014 at 20:59
• $\begingroup$ This should be the selected answer $\endgroup$ –  Andrew Kozak Commented Mar 31, 2016 at 0:18

I think the dominant effect might actually be the fact that the salt you add might not be at boiling temperature. But this is just based on the fact that the boiling-point elevation due to salt in water is actually quite low for typical amounts of salt used in cooking, say. I'm not too familiar with the second effect you mention though.

• $\begingroup$ This is not the dominant effect. $\endgroup$ –  Ron Maimon Commented Jul 15, 2012 at 8:14

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Dr Karl › Dr Karl's Great Moments In Science

Salt in the water

When it comes to fast food at home, pasta is perfect. But does adding a dash of salt really cook it quicker? Dr Karl has been in the kitchen turning up the heat.

By Karl S. Kruszelnicki

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• Audio: Salt in the water (ABC Science)

If you watch somebody cooking pasta, you’ll almost always see them adding some salt to the water. When you ask why, they’ll say they add the salt either to improve the flavour, or to make the water boil at a higher temperature so that the pasta cooks faster.

When you add heat to water, you turn the liquid water into steam. The steam expands, and in doing so, has to push against the surrounding atmosphere. That’s why water doesn’t always boil at 100° C.

At high altitudes the atmospheric pressure is low, so water will boil at a lower temperature. In the Himalayas, I saw our porters bring the water to the boil, and add spaghetti – but it never fully cooked. We were about 12,000 feet (3,658 metres) above sea level.

At that altitude, the boiling point of water is only 88° C. No matter how long they boiled the water, it would never get hotter than 88° C, and so the pasta was always a little crunchy.

The opposite situation happens inside a pressure cooker. The pressure is significantly higher than atmospheric pressure, so the water won’t boil until it gets to 120° C. This higher temperature really speeds up the cooking.

The claim is that adding salt to water does the same. It increases the temperature at which the water boils, which then supposedly cooks the pasta more quickly.

Now water is a very common, but very unusual, liquid. It has kept the physicists and chemists guessing for the last century-and-a-half. That’s a big achievement for such a simple chemical, which has only two atoms of hydrogen married to just one atom of oxygen.

First, compare H 2O to other similar liquids. The easy way to do this is to use the Periodic Table of The Elements, and look at the elements that are similar to oxygen, and then marry them to hydrogen. These chemicals turn out to be H 2S, H 2Se, H 2Te. These chemicals have very low boiling points, but H 2O bucks the trend. You would predict (from the graph) that its boiling point would be -50° C – instead, +100° C. That’s 150 C° higher than expected.

The second weird thing about water, is that as you cool it, it becomes more dense (which you would expect) until it hits 4° C. Then it becomes less dense. This very unusual behaviour is still not explained.

And third, we still don’t fully understand how water boils. The water molecule is shaped like a microscopic right-angled boomerang. There’s a negatively charged oxygen atom in the middle of the "V", and two positively charged hydrogen atoms, one on each end of the boomerang’s arms.

In regular water, the H 2O molecules jostle around until the positive charge of one molecule attracts the negative charge of another. As you heat up the water, you put more energy into the system and these positive-negative attraction bonds start breaking.

Surprisingly, it seems that as these attraction bonds break, that they create a microscopic cavity completely empty of water molecules. Smaller cavities merge to make bigger cavities, which in turn somehow lead to molecules of water breaking free into the atmosphere. Yes folks, we’ve reached boiling point.

And yes, adding salt to water changes things. In pure water, the water molecules are all fairly organized. When you throw in some salt, its molecules can wander around almost at random. These extra molecules increase the disorder, and this "magically" increases the temperature at which the water boils. (If you want to know more, look up any Second Year Physics textbook on Phase Equilibria and the Clausius-Clapeyron equation.)

So yes, salt increases the boiling temperature, but not by very much. If you add 20 grams of salt to five litres of water, instead of boiling at 100° C, it’ll boil at 100.04° C.

So a big spoon of salt in a pot of water will increase the boiling point by four hundredths of a degree! So adding salt to water will not cook your pasta faster – unless your watch is calibrated in microseconds.

If you are in that much of a hurry, you should run with your pasta to the dining table, not walk. Just be happy with the knowledge that salt does improve the flavour.

Tags: science-and-technology , chemistry , physics

Published 12 April 2007

© 2024 Karl S. Kruszelnicki Pty Ltd

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Making Science Fun, Easy to Teach and Exciting to Learn!

Science Experiments

Easy Water Temperature Science Experiment + Video & Lab Kit

Can you see thermal energy? Yes, with just a few common kitchen items!

Although we can explain that molecules move faster when hot and slower when cold, in this science experiment kids will be able to see thermal energy in action and explore the concept hands-on.

We’ve included a materials list, printable instructions, and a simple explanation of how the experiment works. Enjoy our demonstration video to get started!

JUMP TO SECTION: Instructions | Video Tutorial | How it Works

Supplies Needed

• 3 Glass Jars
• Room Temperature Water
• Food Coloring

Water Temperature Science Lab Kit – Only $5

Use our easy Water Temperature Science Lab Kit to grab your students’ attention without the stress of planning!

It’s everything you need to  make science easy for teachers and fun for students  — using inexpensive materials you probably already have in your storage closet!

Water Temperature Science Experiment Instructions

Step 1 – Begin by preparing three identical jars of water. Fill one jar with cold water, one jar with room temperature water, and one jar with hot water.

Helpful Tip: For cold water, fill the jar and put it in the fridge for an hour or two. For the room temperature water, fill the jar and leave it on the counter for an hour or two. For the hot water, boil the water on the stove or put it in the microwave for a minute or two.

Before moving to the next step, take a moment to observe the jars. The temperature of water should be the only difference. Do you think the water temperature will impact what happens when the food coloring is added to each jar? Write down your hypothesis (prediction) and then continue the experiment to see if you were correct.

Step 2 – Place 2-3 drops of food coloring in each jar and observe what happens.

You’ll notice right away that the food coloring behaves differently in each jar. Was your hypothesis correct? Do you know why the food coloring slowly mixed with the cold water and quickly mixed with the hot water? Read the how does this experiment work section before to find out the answer. 

Video Tutorial

How Does The Experiment Work?

When observing the food coloring in the water, you will immediately notice that it behaves differently based on the temperature of the water.

Even though the glasses of water look the same, the difference in the water temperature causes the molecules that make up the water to behave differently. Molecules that make up matter move faster when they are warmer because they have more thermal energy and slower when they are colder because they have less thermal energy. In this experiment, the molecules in the hot water are moving around much faster than the molecules in the cold water.

Thermal Energy is the total energy of the particles in an object.

When placed into water, food coloring will begin to mix with the water. The food coloring will mix the fastest in the hot water because the molecules are moving fast due to their increased thermal energy. These fast-moving molecules are pushing the molecules of food coloring around as they move, causing the food coloring to spread faster.

The food coloring in the room temperature water will take longer to mix with the water because the molecules are moving more slowly due to their decreased thermal energy.

Lastly, the food coloring in the cold water will take a long time to mix with the water because the molecules are moving even slower due to a further decrease in thermal energy.

More Science Fun

Eventually, the food coloring will mix throughout all of the jars. Expand on the experiment, by estimating how long it will take to mix with the water in each jar. Then set a timer and find out how close your estimate was.

In addition, you can also try these other fun experiments using water and food coloring:

• Walking Water Science Experiment – Can water walk upwards against gravity? No, not really, but what makes water seem like it defies gravity is what we’re going to explore in this easy science experiment.
• Color Changing Walking Water Science Experiment   – Much like the regular walking water science experiment, but with an added “colorful” twist.
• Coloring Changing Water Science Experiment – Science or magic? Try this experiment at home with your kids and watch their eyes light up as you pour the liquid into the bowl and “create” a new color.

Water Temperature Experiment

• Three Glass Jars

Instructions

• Begin by preparing three jars of water. Fill one with cold water, one with room temperature water, and one with hot water. Helpful Tip: For cold water, fill the jar and put it in the fridge for an hour or two. For the room temperature water, fill the jar and leave it on the counter for an hour or two. For the hot water, boil the water on the stove or put it in the microwave for a minute or two.
• Place 2-3 drops of food coloring in each jar.
• Observe what happens to the food coloring. Does it behave differently in each jar?

Reader Interactions

May 5, 2017 at 1:17 pm

thank you for u showing my kids this they love it.

March 30, 2019 at 11:58 pm

You’re amazing!!!!

April 7, 2022 at 10:35 am

I like it a lot it’s so cool that I did it for my class and got a A+

March 9, 2022 at 6:10 pm

I will be using this at Parent Science Night tomorrow!

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37 Water Science Experiments: Fun & Easy

We’ve curated a diverse selection of water related science experiments suitable for all ages, covering topics such as density, surface tension, water purification, and much more.

These hands-on, educational activities will not only deepen your understanding of water’s remarkable properties but also ignite a passion for scientific inquiry.

So, grab your lab coat and let’s dive into the fascinating world of water-based science experiments!

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1. walking water science experiment.

This experiment is a simple yet fascinating science experiment that involves observing the capillary action of water. Children can learn a lot from this experiment about the characteristics of water and the capillary action phenomenon. It is also a great approach to promote scientific curiosity and enthusiasm.

Learn more: Walking Water Science Experiment

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A water filtering experiment explains how to purify contaminated water using economical supplies. The experiment’s goal is to educate people about the procedure of water filtration, which is crucial in clearing water of impurities and contaminants so that it is safe to drink.

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3. Water Cycle in a Bag

The water cycle in a bag experiment became to be an enjoyable and useful instructional exercise that helps students understand this idea. Participants in the experiment can observe the many water cycle processes by building a model of the water cycle within a Ziplock bag.

4. Cloud in a Jar

The rain cloud in a jar experiment is a popular instructional project that explains the water cycle and precipitation creation. This experiment is best done as a water experiment since it includes monitoring and understanding how water changes state from a gas (water vapor) to a liquid (rain) and back to a gas.

Learn more: Cloud in a Jar

5. The Rising Water

The rising water using a candle experiment is a wonderful way to teach both adults and children the fundamentals of physics while also giving them an exciting look at the properties of gases and how they interact with liquids.

6. Leak Proof Bag Science Experiment

In the experiment, a plastic bag will be filled with water, and after that, pencils will be inserted through the bag without causing it to leak.

The experiments explain how the plastic bag’s polymer chains stretch and form a barrier that keeps water from dripping through the holes the pencils have produced.

Learn more: Leak Proof Bag Science Experiment

7. Keep Paper Dry Under Water Science Experiment

The experiment is an enjoyable way for demonstrating air pressure and surface tension for both adults and children. It’s an entertaining and engaging technique to increase scientific curiosity and learn about scientific fundamentals.

Learn more: Keep Paper Dry Under Water Science Experiment

8. Frozen Water Science Experiment

The Frozen Water Science Experiment is a fun and engaging project that teaches about the qualities of water and how it behaves when frozen.

You can gain a better knowledge of the science behind the freezing process and investigate how different variables can affect the outcome by carrying out this experiment.

9. Make Ice Stalagmites

10. Bending of Light

A fascinating scientific activity that explores visual principles and how light behaves in different surfaces is the “bending of light” water experiment. This experiment has applications in physics, engineering, and technology in addition to being a fun and interesting method to learn about the characteristics of light.

11. Salt on a Stick

This experiment is an excellent way to catch interest, engage in practical learning, and gain a deeper understanding of the characteristics of water and how they relate to other substances. So the “Salt on Stick” water experiment is definitely worth trying if you’re looking for a fun and educational activity to try!

Learn More: Water Cycle Experiment Salt and Stick

12. Separating Mixture by Evaporation

This method has practical applications in fields like water processing and is employed in a wide range of scientific disciplines, from chemistry to environmental science.

You will better understand the principles determining the behavior of mixtures and the scientific procedures used to separate them by performing this experiment at home.

13. Dancing Spaghetti

Have you ever heard of the dancing spaghetti experiment? It’s a fascinating science experiment that combines simple materials to create a mesmerizing visual display.

The dancing spaghetti experiment is not only entertaining, but it also helps you understand the scientific concepts of chemical reactions, gas production, and acidity levels.

14. Magic Color Changing Potion

The magic color-changing potion experiment with water, vinegar, and baking soda must be tried since it’s an easy home-based scientific experiment that’s entertaining and educational.

This experiment is an excellent way to teach kids about chemical reactions and the characteristics of acids and bases while providing them an interesting and satisfying activity.

15. Traveling Water Experiment

In this experiment, you will use simple objects like straws or strings to make a path for water to pass between two or more containers.

Learn more: Rookie Parenting

16. Dry Erase and Water “Floating Ink” Experiment

The dry-erase and water “floating ink” experiment offers an interesting look at the characteristics of liquids and the laws of buoyancy while also being a great method to educate kids and adults to the fundamentals of science.

Learn more: Dry Erase and Water Floating Ink Experiment

17. Underwater Candle

In this experiment, we will investigate a connection between fire and water and learn about the remarkable factors of an underwater candle.

18. Static Electricity and Water

19. Tornado in a Glass

This captivating experiment will demonstrate how the forces of air and water can combine to create a miniature vortex, resembling a tornado.

Learn more: Tornado in a Glass

20. Make Underwater Magic Sand

Be ready to build a captivating underwater world with the magic sand experiment. This experiment will examine the fascinating characteristics of hydrophobic sand, sometimes referred to as magic sand.

21. Candy Science Experiment

Get ready to taste the rainbow and learn about the science behind it with the Skittles and water experiment! In this fun and colorful experiment, we will explore the concept of solubility and observe how it affects the diffusion of color.

Density Experiments

Density experiments are a useful and instructive approach to learn about the characteristics of matter and the fundamentals of science, and they can serve as a starting point for further exploration into the fascinating world of science.

Density experiments may be carried out with simple materials that can be found in most homes.

This experiment can be a great hands-on learning experience for kids and science lovers of all ages.

22. Super Cool Lava Lamp Experiment

The awesome lava lamp experiment is an entertaining and educational activity that illustrates the concepts of density and chemical reactions. With the help of common household items, this experiment involves making a handmade lava lamp.

Learn more: Lava Lamp Science Experiment

23. Denser Than you Think

Welcome to the fascinating world of density science! The amount of matter in a particular space or volume is known as density, and it is a fundamental concept in science that can be seen everywhere around us.

Understanding density can help us figure out why some objects float while others sink in water, or why certain compounds do not mix.

24. Egg Salt and Water

Learn about the characteristics of water, including its density and buoyancy, and how the addition of salt affects these characteristics through performing this experiment.

25. Hot Water and Cold-Water Density

In this experiment, hot and cold water are put into a container to see how they react to one other’s temperatures and how they interact.

Sound and Water Experiments

Have you ever wondered how sound travels through different mediums? Take a look at these interesting sound and water experiments and learn how sounds and water can affect each other.

26. Home Made Water Xylophone

You can do this simple scientific experiment at home using a few inexpensive ingredients to create a handmade water xylophone.

The experiment demonstrates the science of sound and vibration and demonstrates how changing water concentrations can result in a range of tones and pitches.

Learn more: Home Made Water Xylophone

27. Create Water Forms Using Sound!

A remarkable experiment that exhibits the ability of sound waves to influence and impact the physical world around us is the creation of water formations using sound.

In this experiment, sound waves are used to generate patterns and shapes, resulting in amazing, intricate designs that are fascinating to observe.

28. Sound Makes Water Come Alive 

These experiments consist of using sound waves to create water vibrations, which can result in a variety of dynamic and captivating phenomena.

29. Water Whistle

The water whistle experiment includes blowing air through a straw that is submerged in water to produce a whistle.

This experiment is an excellent way to learn about the characteristics of sound waves and how water can affect them.

Water Surface Tension Experiments

You can observe the effects of surface tension on the behavior of liquids by conducting a surface tension experiment.

By trying these experiments, you can gain a better understanding of the properties of liquids and their behavior and how surface tension affects their behavior.

30. Floating Paperclip

In this experiment, you will put a paper clip on the top of the water and observe it float because of the water’s surface tension.

31. Water Glass Surface Tension

Have you ever noticed how, on some surfaces, water drops may form perfect spheres? The surface tension, which is a characteristic of water and the cohesive force that holds a liquid’s molecules together at its surface, is to blame for this.

32. Camphor Powered Boat

The camphor-powered boat experiment is a fun and fascinating way to explore the principles of chemistry, physics, and fluid mechanics. In this experiment, a miniature boat is used to travel across the water’s surface using camphor tablets.

33. Pepper and Soap Experiment

The pepper in a cloud experiment is a simple and interesting activity that explains the concept of surface tension. This experiment includes adding pepper to a bowl of water and then pouring soap to the mixture, causing the pepper to move away from the soap.

Learn more: Pepper and Soap Experiment

Boiling Water Experiments

Experiments with boiling water are an engaging and informative way to learn about physics, chemistry, and water’s characteristics.

These investigations, which include examining how water behaves when it changes temperature and pressure, can shed light on a variety of scientific phenomena.

It’s important to take the proper safety measures when performing experiments with hot water. Boiling water can produce steam and hot particles that are dangerous to inhale in and can result in severe burns if it comes into contact with skin.

34. Make It Rain

This experiment can be accomplished using basic supplies that can be found in most homes, make it an excellent opportunity for hands-on learning for both kids and science lovers.

Learn more: Make it Rain

35. Fire Water Balloons

Learning about the fundamentals of thermodynamics, the behavior of gases, and the effects of heat on objects are all made possible by this experiment.

36. Boil Water with Ice

The Boiling Water with Ice experiment is an engaging and beneficial approach to learn about temperature and the behavior of water. It can also serve as an introduction for further discovery into the wonderful world of science.

37. Boil Water in a Paper Cup

The “boil water in a cup” experiment is an easier but powerful approach to illustrate the idea of heat transmission by conduction. This experiment is often used in science classes to teach students about thermal conductivity and the physics of heat transfer.

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• Top 50 Fun Food Science Experiments

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Testing the hardness of water

In association with Nuffield Foundation

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Try this experiment with your students to measure the hardness of different water samples and investigate the effect of boiling hard water

This is a student practical, where a lot of the preparation work has been done beforehand. It could be varied so that the students watched, or carried out themselves, the preparation of the solutions. This would require using real (or simulated) sea water, rather than mixing temporarily and permanently hard water. The temporarily hard water will also really need to be boiled and cooled (as opposed to distilled water being substituted).

For younger, or less practically experienced students, consider providing the burettes already clamped and full of soap solution.

Students should bring their conical flasks to the stock bottles of solutions A to E and use a dedicated measuring cylinder for each solution to obtain 10 cm 3 . With larger groups, consider telling different groups to start with a different letter.

The work as described will take about 45 minutes.

• Eye protection
• Measuring cylinders (10 cm 3 ), x5 (one for each of the solutions A to E)
• Conical flask (100 cm 3 )
• Bung, to fit the conical flask
• Burette and burette stand
• Small funnel
• Soap solution in IDA (industrial denatured alcohol), (HIGHLY FLAMABLE, HARMFUL), 75 cm 3 per group (see note 3)
• A supply of distilled or deionised water for rinsing flasks between experiments
• Solution A: deionised water, labelled as ‘Rain water’
• Solution B: a 50:50 mixture of temporarily and permanently hard water, labelled as ‘Sea water’
• Solution C: temporarily hard water, labelled as ‘Temporarily hard water’ 
• Solution D: deionised water, labelled as ‘Boiled temporarily hard water’
• Solution E: permanently hard water, diluted 50:50 with deionised water and labelled as ‘Boiled sea water’ 

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection throughout.
• Soap solution in ‘ethanol’ (industrial denatured alcohol, IDA – see CLEAPSS Hazcard  HC040A , HIGHLY FLAMMABLE, HARMFUL) can be purchased or made up. Genuine liquid soap or soap flakes, from which the liquid can be made, are increasingly difficult to obtain. Wanklyn’s and Clarke’s soap solutions should still be available from chemical suppliers. Lux soap flakes are ideal for making liquid soap if you can source them. Granny’s Original and other non-branded soap flakes work fine but need to be used in solution as soon as they are made. They do not form a stable emulsion and precipitate out overnight. Note that most liquid hand washes are based on the same detergents as washing-up liquids and do not contain soap. To obtain soap solution from soap flakes, dissolve soap flakes (or shavings from a bar of soap) in ethanol (use IDA). See CLEAPSS Recipe Book RB000. Do not dissolve in water.
• Dilute about 150 cm 3  of limewater (IRRITANT, see note 5) with an equal volume of distilled water. Pass in carbon dioxide (see Generating, collecting and testing gases ), taking care that the gas carries over no acid spray, whereupon calcium carbonate is soon precipitated. Continue the passage of gas until all the precipitate dissolves, giving a solution of calcium hydrogen carbonate. This is temporarily hard water.
• Limewater (calcium hydroxide solution) (IRRITANT) – see CLEAPSS Hazcard  HC018  and CLEAPSS Recipe Book RB020.
• Stir a spatula or two of hydrated calcium sulfate – see CLEAPSS Hazcard  HC019B – into some deionised water. Swirl to mix, allow to stand, then decant off the clear solution. This is permanently hard water.

Source: Royal Society of Chemistry

Apparatus required for testing the hardness of different water samples

• Collect about 75 cm 3  of soap solution in a small beaker.
• Set up a burette and, using the small funnel, fill it with soap solution.
• Rain water (solution A)
• Sea water (solution B)
• Temporarily hard water (solution C)
• Boiled temporarily hard water (solution D)
• Boiled sea water (solution E)
• Read the burette. Add 1 cm 3  of soap solution to the water in the conical flask. Stopper the flask and shake it. If a lather appears that lasts for 30 seconds, stop and read the burette.
• If no lather forms, add another 1 cm 3  of soap solution. Shake the flask. Repeat the process until a lather forms that lasts for 30 seconds. Read the burette.
• Rinse out the flask with distilled water. Repeat the experiment with 10 cm 3  of another water sample, until you have tested them all. Make a note of the volumes of soap solution that were needed in each case to produce a lather.
• Which water samples are ‘soft’ and why
• Whether sea water contains permanent hardness, temporary hardness or a mixture of both.

Teaching notes

Sample A will require very little soap solution. This shows that rain water is soft. It has effectively been distilled (and like distilled water, it will contain dissolved carbon dioxide but no salts).

Sample D will also require very little soap. This shows that temporarily hard water can be softened by boiling (see theory below).

The other samples will require more soap but E will require less than B, showing that sea water contains both temporary and permanent hardness.

The volumes of soap solution needed give a measure of the relative hardness of the various samples. With more able groups, it might be worth considering that rainwater is completely soft, so that the volume of soap required here is just the amount required to get a lather, not to overcome hardness. This volume should be subtracted from the other volumes before the relative hardnesses are compared.

Hard water contains dissolved calcium (or magnesium) salts that react with soap solution to form an insoluble scum that should be seen as a white cloudiness in the tubes:

calcium salt(aq) + sodium stearate (soap)(aq) → calcium stearate (scum)(s) + sodium salt(aq)

Only when all the calcium ions have been precipitated out as scum will the water lather. Thus the volume of soap solution measures the amount of hardness.

Temporarily hard water is defined as that which can be softened by boiling. The reactions by which it is made here are:

Ca(OH) 2 (aq) + CO 2 (g) → CaCO 3 (s) + H 2 O(l)

(Calcium carbonate is the ‘milkiness’ that forms when lime water is reacted with carbon dioxide.)

CaCO 3 (s) + CO 2 (g) + H 2 O(l) → Ca(HCO 3 ) 2 (aq) (calcium hydrogen carbonate)

This reaction also occurs when rain water (containing dissolved carbon dioxide) flows over limestone rocks. On boiling, the reaction is reversed, softening the water:

Ca(HCO 3 ) 2 (aq) → CaCO 3 (s) + CO 2 (g) + H 2 O(l)

Permanently hard water contains calcium or magnesium salts other than the hydrogen carbonates. These are unaffected by boiling.

Additional information

This is a resource from the  Practical Chemistry project , developed by the Nuffield Foundation and the Royal Society of Chemistry.

Practical Chemistry activities accompany  Practical Physics  and  Practical Biology .

© Nuffield Foundation and the Royal Society of Chemistry

• 14-16 years
• 16-18 years
• Practical experiments
• Practical skills and safety
• Investigation
• Applications of chemistry

Specification

• Hard water is a term used to describe water containing high levels of dissolved metal ions. When soap is used in hard water, scum, an insoluble precipitate, is formed.
• (i) the causes of hardness in water and how to distinguish between hard and soft waters by their action with soap
• Hardness in water. Causes of temporary and permenant hardness.
• Removal of hardness by boiling and ion exchange.

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Changing Water's Boiling Point Mark as Favorite (21 Favorites)

LAB in Physical Properties , Concentration , Colligative Properties , Boiling Point , Accuracy , Graphing , Molality , Boiling Point Elevation , Error Analysis . Last updated June 22, 2022.

In this lab, students will explore colligative properties in a quantitative approach. They will measure the effect of increasing the molality of a salt solution on the solution’s boiling point, and they will graph their data and use the slope of the line of best fit to calculate the boiling point elevation constant of water. There are three versions of the lab, some of which provide more structure and guidance and others of which are more student-driven.

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the following scientific and engineering practices:

• Asking Questions and Defining Problems
• Using Mathematics and Computational Thinking
• Analyzing and Interpreting Data
• Planning and Carrying Out Investigations

By the end of this lab, students should be able to:

• Experimentally determine the boiling point elevation constant of water.
• Evaluate the accuracy of their experimental value against the accepted value.
• Explain how adding different amounts of solute to water changes the boiling point of water.
• Design an experiment to measure the effect of the concentration of a solute on a solution’s boiling point. ( Student Activity C only )

Chemistry Topics

This lab supports students’ understanding of:

• Colligative properties
• Boiling point
• Experimental Design ( Student Activity C )

Teacher Preparation : 15 minutes

Lesson : 60–120 minutes (depending on which version of the lab you do)

For each group:

• 250-mL beakers (5)
• NaCl (noniodized)
• Distilled water
• Hot plate (or Bunsen burner and ring stand)
• Thermometer or temperature probe
• 250-mL beaker
• Beaker label or grease pen
• Weighing boat
• Stirring rod
• Always wear safety goggles when working in the lab.
• Exercise caution when using a heat source. Hot plates should be turned off and unplugged as soon as they are no longer needed.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• Students will be graphing their experimental data and using the slope of the line of best fit to calculate the boiling point elevation constant for water. Be sure students are familiar with proper graphing techniques. The AACT Graphing Simulation could be a useful resource to review before doing this lab.
• Be sure to use pure NaCl (i.e. don’t use iodized salt that you might find at the grocery store), since the molar mass (needed to calculate molality) and the i value won’t be quite the same as if it were pure NaCl, and it will skew the calculations.
• This lab works with a relatively small percent error.
• This is a cheap and relatively quick experiment, and it is easy to prep and clean. Students can just dispose of the salt water down the sink when they are done and clean any equipment they used with soap and water.
• Be sure that students are aware that the “change in boiling point” calculation compares the boiling point of each salt solution to the boiling point of pure water (the 0 m “solution”).
• There is some information about boiling point elevation included in the background information, but you may want to introduce students to the concept of molality and the equation for boiling point elevation and its variables before performing this lab.
• Students are instructed to measure the boiling point of 5 solutions of different concentrations. To have more data points, you could have all the groups report their data for each concentration to share with the class, which would limit the effect of outliers on their calculations. Alternatively, you could have each group do multiple trials for each concentration (repeating steps 1-3 in Student Activity A, or steps 1-6 in Student Activity B). In that case, be sure to increase the amount of solution each group is instructed to prepare, allow more time for repeated trials, and add lines to the data table for each trial and an average.
• You can also shorten this by assigning one concentration to each group and have students share data if time is an issue, though this allows more room for error with fewer data points. Another way to save time would be to prepare the solutions for students in advance of the lab period, though this puts more of the burden on the teacher and does not give students the same visual understanding of how much salt is in each solution if they are not preparing them themselves.
• Student Activity A requires the students to complete calculations in the prelab questions to help them determine how to prepare the various NaCl molality solutions required in the experiment. You may want to check the prelab questions or review them as a class before students start preparing their solutions. To increase the challenge further, you could remove the explicit instructions for how to use the line of best fit to calculate K B .
• Student Activity B is a more traditional “cookbook” lab that provides the correct amounts of salt for each molality for your students.
• Lesson Plan: How to Write a Formal Lab
• From Chemistry Solutions , September 2016: Tools and Strategies for Teaching Lab Report Writing
• Since Student Activity C is a lot more student-centered and has students posing a question and designing procedures to answer that question, it will take substantially longer than the other versions of this lab. Designing an experiment can be very challenging for students, as many of them have never had to do it before, which makes it a very valuable experience for them to practice this important scientific skill.
• Be sure that you approve students’ procedures before they start conducting their investigation if you use Student Activity C. Make sure they are taking the appropriate safety precautions. Note that you should primarily be checking for safety – as long as they are not completely off-base, it’s ok if there are minor flaws in their experimental design! They will learn more from making the mistake and having to fix it than from you pointing it out!
• For all versions of the student activity, students are required to graph their data and use a line of best fit to calculate the K B value for water. They will get the best results if they use a digital temperature probe (rather than a thermometer) to collect more accurate data and Excel or a similar graphing program to create their graphs, as it will generate a line of best fit for them. They can also use the “Set Intercept” function to set the y-intercept as 0, since they should anticipate that 0 g of salt will change the boiling point by 0°C, as that is the baseline. This will make it so the equation for the line of best fit has a y-intercept of 0 and is in the form y = mx .

For the Student A

Solutions are homogeneous mixtures of solute and solvent. The solvent is the most abundant substance in a solution. In a liquid solution, the solvent does the dissolving. The solute is the other substance in a solution. In a liquid solution, the solute is dissolved. It is possible for a solution to have more than one solute, air is an example, but a solution can have only one solvent.

The boiling point of a substance is defined as the temperature at which a liquid becomes a gas. When a substance boils, the molecules gain enough energy to “break free” of the other molecules and escape as a gas. Dissolving a solute in a solvent increases the boiling point. This boiling point elevation is a colligative property, which means that it is dependent only the amount, not type, of solute that is dissolved in the solvent. Keep in mind that when ionic solids are dissolved in water they break up into ions. So NaCl will break up into two ions, MgCl 2 will break up into three ions, and AlCl 3 breaks up into four ions. The number of ions that the substance breaks up into is referred to as the Van’t Hoff factor. The equation for calculating boiling point elevation is ∆T B =imK B , where ∆ T B is the change in the boiling point (°C), i is the Van’t Hoff factor, m is the concentration (molality, m), and K B is the boiling point elevation constant for the solvent (°C/m).

Prelab Questions

• Define molality .
• How will you know when a solution has reached its boiling point?

To determine how adding a solute to water will affect the boiling point of water.

• NaCl (non-iodized)
• Hot plate (or Bunsen burner and ring stand) to heat solutions to boiling
• Tongs or hot hands to move hot beakers
• Always wear safety goggles when handling chemicals in the lab.
• Wash your hands thoroughly before leaving the lab.
• Follow the teacher’s instructions for cleanup of materials and disposal of chemicals.
• Prepare 100 mL of each of the following NaCl solutions using your calculations from the prelab questions: 0 m, 0.5 m, 1.0 m, 1.5 m, and 2.0 m. Make sure you are using non-iodized NaCl and distilled water.
• Heat each solution until it boils and record the boiling point.
• Determine the change in boiling point for each concentration of the solution and record it the table below.
• Clean up your work station. Salt water solutions can be poured down the drain. Thoroughly wash and dry all equipment.

• Use your data to graph the relationship between concentration (x) and change in boiling point (y). You may use a program such as Excel to create your graph or you may neatly draw it on graph paper. Attach a copy of your graph when you turn in your lab.
• Determine the equation of the best fit line from your graph.
• Recall the equation for boiling point elevation: ∆T B =imK B
• Since the change in boiling point is your y variable and the molality is your x, that leaves iK B as the slope. Call the slope A: ∆T B /m = iK B = A
• Take the slope of the line and divide it by the Van’t Hoff factor, i, to determine your experimental K B : K B = A/i . Show your calculations in the space below.
• Calculate the percent error compared to the accepted value for water’s K B , 0.512 °C/ m .
• How do you think the temperature change would be affected if you prepared solutions of CaBr 2 (of the same molalities) instead of NaCl? Why?

Write 1–2 paragraphs responding to the following questions to summarize what you have learned in this lab:

• Make a general statement about what happens to the boiling point of a solution as concentration increases, citing data from your experiment as evidence.
• Research and find an application of this statement. Cite your sources.
• Give one possible lab error that would have resulted in the percent error calculated in question 4.

For the Student B

• 0.0 m solution: 99.8 g distilled water + 0 g NaCl
• 0.5 m solution: 99.8 g distilled water + 2.91 g NaCl
• 1.0 m solution: 99.8 g distilled water + 5.83 g NaCl
• 1.5 m solution: 99.8 g distilled water + 8.74 g NaCl
• 2.0 m solution: 99.8 g distilled water + 11.7 g NaCl
• Use a hot plate to heat the 0.0 m sample until it comes to a rolling boil. (Recall that the temperature will stay constant once the water reaches its boiling point.)
• Use a temperature probe or thermometer to measure the boiling point of the solution. Be sure that the probe or thermometer does not touch the bottom or sides of the beaker. Record the boiling point in the table below.
• Using tongs or hot hands, remove the beaker from the hot plate and set it aside to cool. (Remember that hot glass and cold glass look the same, so be careful!)
• Repeat steps 2–5 for the remaining four solutions (0.5 m, 1.0 m, 1.5 m, 2.0 m).

For the Student C

In this investigation, you will collect evidence that will show you the effect that solution concentration has on its boiling point. The boiling point of a substance is defined as the temperature at which a liquid becomes a gas. A substance boils when the molecules have enough energy to overcome the vapor pressure of the surrounding air and change from a liquid to a gas. When a substance boils, the molecules gain enough energy to “break free” of the other molecules and escape as a gas. Keep in mind that substances with higher intermolecular forces boil at a higher temperature than those with lower intermolecular forces. To read more about this process and see a simulation, go to: http://www.chem.purdue.edu/gchelp/liquids/boil.html .

Solutions are homogeneous mixtures of a solute and solvent. Dissolving a solute in a solvent increases the boiling point. In this investigation the solvent will be water and the solute will be sodium chloride (NaCl). When you add salt to water, sodium chloride dissociates into sodium and chloride ions. These charged ions interfere with the intermolecular forces between water molecules. Since the water molecule is a dipole, the oxygen is more negative and is attracted by the positive sodium ions. The hydrogen side is more positive and is attracted to the chloride ions.

Boiling point elevation is a colligative property, which means that it is dependent only the amount, not type, of solute that is dissolved in the solvent. Keep in mind that when ionic solids are dissolved in water they break up into ions. So NaCl will break up into two ions, MgCl 2 will break up into three ions, and AlCl 3 breaks up into four ions. The number of ions that the substance breaks up into is referred to as the Van’t Hoff factor. The equation for calculating boiling point elevation is , where D T B is the change in the boiling point (°C), i is the Van’t Hoff factor, m is the concentration (molality, m), and K B is the boiling point elevation constant for the solvent (°C/m).

Asking Questions

After you view the simulation above and read through the information, develop one or more scientific questions about boiling point elevation that you can answer in this investigation.

Preparing to Investigate

Before beginning the investigation, thoroughly review the rest of this document, including the outline on the last page for guidance on the lab report that you will submit after completing your investigation.

Once you have identified a question you will investigate, develop procedures that you will follow to gather data about the effect that solution concentration has on its boiling point. Make a note about safety concerns that are relevant for your procedures. Be sure to include a list of materials and equipment you will need. You must have your teacher approve your procedures before you begin. Additionally, think about the observations you will make and the data that you will need to collect during each part of the investigation and prepare appropriate data and observation tables.

Gathering Evidence

• Wear goggles and a lab apron throughout the investigation.
• When using a temperature probe, be sure that it does not touch the bottom or side of the container.
• Hot and cold glassware look alike. Take caution when using glassware that has been heated.
• Pour all liquid waste in the waste beaker located in the back of the lab.
• Since you will be looking at the effect of the concentration of a solution on its boiling point, you should be sure to collect data about the boiling point of pure water.
• Prepare at least three different NaCl solutions, each with a different molality.
• Decide how many times you need to repeat each trial.

Analyzing Evidence

• What was the molality of each of the solutions you prepared? Please show all support calculations.
• What was the average change in the boiling point (°C) for each of the solutions when compared to the boiling point of pure water?

Interpreting Evidence

• Use your data to graph the relationship between concentration (x) and change in boiling point (y).
• Use the equation of your best fit line and the equation  to calculate the boiling point elevation constant (K B ) of water. Include units.

Making Claims

• Research an everyday application of this statement. Cite your sources.
• In your own words and using evidence from the investigation, answer the scientific question(s) that you posed at the beginning of the investigation.

Reflecting on the Investigation

• Think about your experimental design for the investigation. Did you need to make any modifications so that your data produced accurate results? Explain.
• Give one possible lab error that would have resulted in the percent error calculated in question 6.
• Suppose that a classmate suggests that the concentration of a solution must also affect its freezing point. Describe a procedure that you would use to test this hypothesis.

You will write up a lab report describing what you did in your investigation and what you learned from it. Your report will need to include everything someone would need if they wanted to replicate your experiment, as well as an analysis of your data. You need to include the following sections:

Include 1–2 paragraphs of background information relevant to the investigation you have planned. This information may come from external research, class notes, your textbook, etc. and should include brief explanations of important terms and concepts.

Problem/Objective

Write a brief scientific question (problem) or statement (objective) of what you plan to investigate in this experiment.

Make a bulleted list of the chemicals, glassware, and other equipment needed to carry out your investigation.

Make note of any safety precautions you will need to observe.

List the step-by-step instructions that would allow another person to repeat your experiment.

Create a data table to record all your data and observations in an organized manner.

Calculations

Show any calculations that you do with your data, including any graphs. This section should address the questions in the “Analyzing Evidence” and “Interpreting Evidence” sections above. Be sure that your work is well organized and easy to follow, and that you include units where needed.

Address the questions in the “Making Claims” section above, and include any other relevant analysis of your data that you’d like to include. This should be one of the longer written sections of your report (several paragraphs), describing how you are interpreting the data you collected and the calculations you performed. You should cite specific data/calculations to support each claim you make in this section.

Address the questions in the “Reflecting on the Investigation” section above. This should be a couple of paragraphs reflecting on the larger themes of how you designed the experiment and how you could improve or expand on it in the future, what the overall results were, and how you answered the scientific question (from the “Problem/Objective” section) you set out to investigate. You can also discuss implications this experiment may have for future research.

Remember Me

Shop Experiment Boiling Temperature of Water Experiments​

Boiling temperature of water.

Experiment #3 from Exploring Physical Science

Introduction

The  physical properties  of a pure substance can be used to identify the substance and distinguish it from other pure substances.  Boiling temperature  is one such physical property. This is the temperature at which a substance changes rapidly from its liquid state into a gas. Rapid formation of bubbles is evidence that the liquid is at its boiling temperature. In this experiment, you will study the boiling of water.

• Observe the boiling of water.
• Measure temperature.
• Analyze data.
• Use your data and graph to make conclusions about boiling.
• Determine the boiling temperature of water.
• Apply the concepts studied in a new situation.

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

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• Classical Physics

Ice and Boiling Water Experiment: Discover the Surprising Results

• Thread starter BL4CKCR4Y0NS
• Start date Mar 19, 2010
• Tags Boiling Ice Water
• Mar 19, 2010
• Creating an 'imprint' on a super photon
• A device to sort photon states could be useful for quantum optical computer circuits
• On the way to optical logic gates: Study demonstrates the basics for purely optical processing of information

BL4CKCR4Y0NS said: If you nearly fill a test tube with cool water and then take a piece of ice and press it down on the bottom of the tube with a small weight, heat the test time with a flame that licks only the upper part of the tube, the water will start to boil sooner or later.But the ice at the bottom will not melt. What's going on?

• Mar 20, 2010

BL4CKCR4Y0NS said: Yeah I took it straight out of a book and didn't understand... So basically it just takes more time for it to melt because heat rises and the ice is at the bottom. Yeah?

• Mar 26, 2010

This experiment demonstrates the concept of superheating, where water can reach a temperature above its boiling point without actually boiling. The ice at the bottom of the test tube acts as a nucleation point, providing a surface for bubbles to form and allowing the water to finally boil. This is because the boiling point of water is affected by pressure, and the weight of the ice creates a higher pressure at the bottom of the tube. As the water heats up, the pressure at the bottom of the tube increases, causing the boiling point to also increase. This allows the water to reach a higher temperature before boiling. Superheating can be a surprising and potentially dangerous phenomenon, as the water can suddenly boil and potentially cause burns or explosions. It is important to always use caution when heating liquids and to never heat water in a completely sealed container.  

FAQ: Ice and Boiling Water Experiment: Discover the Surprising Results

1. what is the purpose of the ice and boiling water experiment.

The purpose of this experiment is to demonstrate the surprising results that occur when ice and boiling water are mixed together, specifically the formation of a vortex or "tornado" of ice cubes in the center of the boiling water.

2. How do you perform the ice and boiling water experiment?

To perform this experiment, you will need a clear glass or plastic container, ice cubes, and boiling water. Fill the container about 3/4 full with boiling water, then drop in a few ice cubes. Watch as the ice cubes sink to the bottom and a vortex forms in the center of the container. You can also add food coloring to the water for a more dramatic effect.

3. Why do the ice cubes sink in the boiling water?

The ice cubes sink in the boiling water because they are denser than the hot water. As the ice cubes melt, the cold water becomes denser and sinks to the bottom, pushing the warmer, less dense water to the top.

4. What causes the vortex or "tornado" in the center of the boiling water?

The vortex is caused by the difference in temperature between the boiling water and the melting ice cubes. As the cold water from the melting ice sinks to the bottom, it creates a circular motion, similar to a whirlpool, in the center of the container.

5. Are there any real-world applications for this experiment?

Yes, this experiment has real-world applications in meteorology and oceanography. It helps to explain the formation of ocean currents and the movement of water in the Earth's atmosphere. It also demonstrates the concept of convection, which is important in understanding weather patterns and climate change.

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Lindsey Kang

Table of Contents

Introduction

Bibliography

Return to Research

How Different Concentrations of Salt Affect the Boiling Point of Water

Background Information:

The boiling point of a liquid is the temperature at which its vapor pressure equals the pressure of the gas above it. One factor that affects the boiling point is the type of molecules that make up the liquid. That is why water, for example, has a different boiling point (100°C) from ethanol (78.4°C). The formula to find boiling point is ΔT = i K b m. The van’t Hoff factor, or i , is a constant associated with the solute. This experiment will be using salt as the solute, and the van’t Hoff factor of NaCl is 2. K b is the ebullioscopic constant. Water will be acting as the solvent in this research, and the K b for water is 0.52 °C/m. M is the molality of a solvent, which is moles solute/kg solvent. According to this equation, different concentrations of salt water will have different boiling points, because the molality will be changing, ultimately affecting the ΔT.

Statement of the Problem:

The purpose of this investigation is to determine the different boiling points at several different concentrations of a NaCl solvent in a fresh water solute.

Hypothesis:

I believe that the greater the concentration of salt within water, the higher the change in temperature will be. The more mass of solvent, the greater the molality will be. Therefore, this will ultimately result in a higher temperature. The independent variable in this experiment is the mass of salt (concentration), and the dependent is the change in temperature in the overall boiling point of water.

Materials .:. Go Up

-Bunsen burner

-Thermometer that can connect to LoggerPro

-1000 mL (1 L) beaker

-Kosher salt

-Electric balance beam

-Saucer/container for salt

Experiment Design .:. Go Up

Procedure .:. Go Up

First, the beaker is filled to 400 mL with sink water and placed on top of the bunsen burner. The burner is then turned on, and the water is brought to a boil. A thermometer must be placed inside of the beaker, so that the computer program LoggerPro may track and graph the changes in the temperature of the water. Measure out 16 grams of salt on an electric balance beam, zeroing out the mass of the container. When the plain, salt-free water reaches its boiling point, cautiously add in the salt. Observe the change in temperature as it rises to a new boiling point. If the water level has gone below 400 mL , pour a little bit more into the beaker until it is at 400 mL again. Repeat this 10 times, pouring in another 16 g of salt with each variation, so that by the end, there is a total of 160 g of salt in the water, (about 40% saturated, close to the highest solubility of salt in water). Find the average boiling point temperature by looking at the plateau on the LoggerPro graph, as the plateau indicates the highest boiling temperature for that particular liquid. Record those boiling point for each increment of salt added in (16, 32, 48, 64, 80, 96 112, 128, 144, 160 g).

Data .:. Go Up

I performed three test trials and took the average of the results. Below is the data table and graph. I also calculated the ideal boiling point using the equation ΔT = i K b m. The constants of this particular equation in relation to salt as a solute and water as a solvent manipulated the  calculations to be 1.04((x/58.4)/0.4), with the x being the amount of salt (g) being added into the solvent. I also added 100 ºC (the established boiling point of water) to the resulting change in temperature (ΔT). I compared the results to my personal data, and recorded the difference in temperature.

Conclusion .:. Go Up

The observed data from my experiment differs slightly from the calculations of the official boiling point equation ΔT = i K b m. The trendline for the observed temperatures is 0.0561x+102. The trendline for the calculated temperatures is 0.0422x+100. Because the coefficient 0.0561 (from the observed temperature trend line) is larger than 0.0422 (calculated temperature trend line), this indicates that during the experiment, the water heated up faster and at a steeper rate than expected compared to the theoretical data. However, the overall data confirms my hypothesis that the higher the concentration of salt in water, the higher the boiling point will be.

One of the obvious errors in this experiment is human error. There were instances during my trials where some of the salt could have escaped as I poured it into the beaker. Therefore, the salt added in might not have been exactly 16 g each time. Also, I observed the change in temperature through LoggerPro . The boiling point can be located on a graph by looking at where it plateaus. Though the program calculated the mean temperature of a certain section, I had to personally select an area where I estimated the plateau to be. Therefore, I could have misjudged the true location. Another source of error is the evaporation of the boiling water. Though I attempted to maintain the water level in the beaker at 400 mL , there is the possibility that as I added in salt, the mass of the water increased, making the ratio of salt to water no longer proportional or at the desired saturation.

Future Improvements:

In a future replication of this experiment, there are some improvements to be made that would produce more accurate results. First of all, the loss of water through evaporation must be accounted for. A method of doing this would be to take the mass of the water every time salt is added in, to make sure the water is still at 400mL, apart from the mass of the added salt. Also, a more quality funnel should be used to ensure that all of the salt lands in the water. Finally, if possible, a more accurate way of observing the boiling point should be used besides the human eye and LoggerPro , such as a program specifically designed to indicate the highest boiling point of a solute.

Bibliography .:. Go Up

- https://www.chemteam.info/Solutions/BP-elevation.html

This website was helpful as it provided the equation required to solve for the boiling points of different solutes.

- https://www.cliffsnotes.com/study-guides/chemistry/chemistry/solutions/freezing-and-boiling-points

This was helpful as it contained many examples of how to solve for boiling points.

- https://www.chem.purdue.edu/gchelp/liquids/boil.html

This site was helpful because it had background information about what boiling point is.

https://chemistry.stackexchange.com/questions/69038/solubility-of-nacl-in-water

This website contained relevant questions and answers about the nature of boiling point and how to find it.

https://study.com/academy/lesson/calculating-boiling-point-elevation-of-a-solution.html

This site provided many visual examples and aids.

The melting and boiling point of water

Core Concept

In this tutorial, you will learn about the melting point, freezing point, and boiling point of water, and some important concepts.

What is water?

Water is a molecule consisting of three atoms, one oxygen atom and two hydrogen atoms. Due to a force called hydrogen bonding , water molecules adhere to one another. Water exists in a gaseous, liquid, and solid state depending on its temperature. On earth, water exists in all three states of matter : solid, liquid, and gas (sometimes called vapour).

Melting Point of water

Melting is a state change of a  solid  into a  liquid  when  heat  is applied. As the temperature rises, the molecules move faster. Once they have reached a specific temperature, they break free from their rigid crystalline structure and begin to move more freely, now in the liquid state. In a pure  crystalline solid , this process occurs at a fixed  temperatur e. The melting point of water is about 32 degrees Fahrenheit (0 degrees Celsius) for pure water at sea level (normal elevation). At other elevations the melting point will change due to different ambient pressure. These changes are discussed further in a section below.

Boiling Point of water

Boiling  is the process when a liquid changes states and turns into a gas. As temperature increases, a molecule will gain enough energy to become a gas, where intermolecular distances become much larger compared to the liquid state. The boiling point for water is 212 ºF or 100 ºC, whereas the boiling point of salt water is about 102 ºC. The boiling point of water will also change at non-standard pressures. Impurities in water, like salt, modify the intermolecular interactions between water molecules that result in a modified boiling point.

Boiling at High Elevations

The standard boiling temperature of water only applies at standard pressures, that is at sea level. As you move to higher elevations (lower pressure) the boiling temperature will decrease.

For example, although water normally boils at 100 o C (212 o F), on Mount Everest (elevation about 27,000 feet) water boils at 68 oC (154 oF).

What if we try to boil water deep in the ocean? In some of the deepest parts of the ocean, water will stay in its liquid state until a temperature of 400 o C (750 o F). Here the pressure is much higher than at normal sea level, and this makes it so more energy (higher temperature) is needed to boil the water.

Definitions:

Melting point -a temperature where a substance can change from its solid state to a liquid state.

Freezing point -the temperature at which a substance undergoes a phase change from a liquid state to a solid-state.

Boiling point – the temperature at which a liquid undergoes a phase change and turns into a vapor.

• Water in its solid form floats instead of sinking when sitting in liquid water. This is different from most other solids.
• Gas can be turned into a liquid or even a solid through pressure.
• The boiling point and freezing point can differ depending on how much salt is in water.
• At higher altitudes, the boiling point of water is lower.

Other Articles on Water

• Properties of Water
• Reaction of Sodium in Water
• Polarity of Water
• Equilibrium of Water

Learning Space

Teachable Moments

Stay Connected

Classroom Activity

Melting ice experiment.

In this activity, students will predict, observe, and compare melt rates of ice under different temperature conditions and in different solutions.

Cool and warm water

Ice cubes (4-6 per group, uniform size and shape)

Food coloring

Thermometers

Colander, mesh strainer, or other similar device

Small bowls (2 per group)

Cloth or paper towels

(Optional) pitchers for pouring water

(Optional) basin for catching poured water

(Optional) funnels

• This activity requires flowing water. If available, a faucet with cold and warm water can be used. Otherwise, use pitchers with warm and cold water. However, note that the rate at which water is poured from a pitcher can vary greatly. Pouring through a funnel can help regulate the flow of water.
• Consider having towels on hand for cleaning up spills and splashes.
• Safety: Hot water can scald. Make sure students are using water that is below 110° F (43° C).
• Use the leftover water from this activity to water a plant or save it for another activity instead of dumping it down the drain.

The Greenland ice sheet is the second largest body of ice in the world right behind the Antarctic ice sheet. As the ice sheet melts, the water flows into the ocean, contributing to global sea level rise.

As glacier ice melts, some of the water can reach the ground below the ice, forming a river that channels glacier water into the ocean. As it flows into the ocean, this cold, fresh meltwater will rise above the warmer, salty ocean water because freshwater is less dense than salt water.

The rising cold water then draws in the warmer ocean water, melting the face of the glacier from the bottom up. This creates an overhang of ice, the edges of which will eventually break off in a process called calving, which quickly adds more ice to the ocean. As ocean waters warm, this calving process speeds up.

This narrated animation shows warm ocean water is melting glaciers from below, causing their edges to break off in a process called calving. Credit: NASA | Watch on YouTube

Understanding these different factors that contribute to Greenland's melting ice sheet is an important part of improving estimates of sea level rise. The Oceans Melting Greenland (OMG) mission was designed to help scientists do just that using a combination of water temperature probes, precise glacier elevation measurements, airborne marine gravity, and ship-based observations of the sea floor geometry. The mission, which ran from 2016 to 2022, provided a data set that scientists can now use to model ocean/ice interactions and improve estimates of global sea level rise.

Part 1: Still Water

Part 2: flowing water, part 3: salt and freshwater.

• Introduce or ask students what they know about glaciers, ice melt, and sea level rise. Consider using the lesson What’s Causing Sea-Level Rise? and having students read 10 Interesting Things About Glaciers from NASA's Climate Kids website prior to this activity. If necessary, remind students that glaciers are huge, long-lasting masses of ice sitting on landmasses that form over many years. Snow accumulates and compresses into glacier ice under the weight of newer layers of snowfall above. Glaciers are not to be confused with icebergs, which are large chunks of glaciers or ice sheets that have broken off and float freely in the ocean.

Fill one container with room-temperature water and a second container with hot water. Image credit: NASA/JPL-Caltech | + Expand image

Place an ice cube in each container of water and time how long it takes the ice to melt. Image credit: NASA/JPL-Caltech | + Expand image

• Ice cube placed in a dish of room temperature water
• Ice cube placed in a dish of hot water
• Ice cube placed under flowing room temperature water
• Ice cube placed under flowing hot water
• Fill one dish with room temperature water.
• Measure and record the temperature.
• Gently place an ice cube in the dish and record how long it takes for the ice cube to melt. There should be enough water in the dish so the ice cube floats.
• Measure and record the water temperature after the ice has melted.
• Repeat the procedure using hot water. These two steps can be done at the same time if students are able to monitor and record the melt time for both cubes of ice.
• Ask students to share their results and observations.

Image credit: NASA/JPL-Caltech | + Expand image

• Mix water with food coloring and freeze into ice cubes (two per group or two as a class demo).
• Tell students they are going to add a colored ice cube to a saltwater solution and to a freshwater solution and allow the ice to fully melt. Ask them to make predictions about what will happen.
• In a clear beaker or plastic container, add 1 teaspoon of salt to 1 cup of water and stir until the salt is dissolved. Allow time for any water movement to stop.
• Pour the same amount of freshwater into a clear beaker or plastic container. Allow time for any water movement to stop.
• Gently add one ice cube to each container, taking care to not disturb the water too much.
• Have students observe each container and take notes. It may be helpful for students to place a white sheet of paper behind the containers to see more details.

The cup on the left (with blue food coloring) contained ice melted in a saltwater solution while the one on the right (with the red food coloring) contained ice melted in a freshwater solution. Image credit: NASA/JPL-Caltech | + Expand image

• If necessary, explain to students that because one container has salt water, and one has freshwater, the less dense meltwater floats on salt water but has the same density and mixes with the freshwater.
• Connect this phenomenon to the movement of fresh meltwater from under a glacier into warm ocean water.
• Which ice cube melted fastest? Which melted slowest? How could these results be altered? Changing the flow rate and temperature of the water will change how quickly the ice melts.
• What do these results tell you about the melting of glaciers in different conditions? Currents of warm ocean water will melt glaciers faster than still water.
• What would happen to cold meltwater that flows out from under a glacier into salty ocean water? The freshwater will rise because of its lower density, drawing in warmer ocean water against the face of the glacier.
• Students should accurately measure and record temperature and melt times.
• High school chemistry students should accurately calculate what the final temperature of the water in the containers will be in Part 1 by using specific heat capacity.
• Ask students to investigate whether ice exposed to warm or room temperature air would melt more quickly or more slowly than ice exposed to still or flowing warm or room temperature water.
• Lower elementary: Ask students to predict what would happen if some of the water was removed from the containers in Part 1 and placed in the freezer. Freeze some of the water to confirm their predictions.
• Upper elementary: Remove some of the salt water from Part 3 and place it on a flat, non-porous surface to dry. Ask students to predict what will happen when the water evaporates. Repeat the process with freshwater. Allow water to dry overnight and compare predictions to observations of what occurred.
• Middle school: Ask students to draw or describe the changes in particle motion, temperature, and state(s) of matter at the beginning and end of their observations.
• High school: Using the known masses and temperatures of the ice cubes and water in Part 1, have students calculate the final temperature of the water in the room temperature bowl and the hot water bowl using the formula m 1 CΔT 1  = m 2 CΔT 2 . Then, have them compare their calculations to observed results.

Explore More

What's Causing Sea-Level Rise? Land Ice Vs. Sea Ice

Students learn the difference between land ice and sea ice and make a model to see how the melting of each impacts global sea level.

Subject Science

Time 30 mins - 1 hr

10 Interesting Things About Glaciers

Learn all about glaciers in this slideshow from NASA's Climate Kids website

Time Less than 30 mins

Lessons in Sea-Level Rise

What is sea-level rise and how does it affect us? This "Teachable Moment" looks at the science behind sea-level rise and offers lessons and tools for teaching students about this important climate topic.

Grades 5-12

Time 30-60 mins

Collection: Climate Change Lessons for Educators

Explore a collection of standards-aligned STEM lessons for students that get them investigating climate change along with NASA.

How Melting Ice Causes Sea Level Rise

Learn the difference between land ice and sea ice, then do an experiment to see how the melting of each contributes to global sea level rise.

Collection: Climate Change Activities for Students

Learn about climate change and its impacts with these projects, videos, and slideshows for students.

Teachable Moments: Reflecting On Greenland’s Melting Glaciers as OMG Mission Concludes

Explore how the OMG mission discovered what's behind one of the largest contributors to global sea level rise. Plus, learn what it means for communities around the world and how to get students engaged.

NASA Greenland Mission Completes Six Years of Mapping Unknown Terrain

To learn how ocean water is melting glaciers, NASA’s Oceans Melting Greenland mission extensively surveyed the coastline of the world’s largest island.

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3.1.3 Yeast experiment explained

You’ve seen the results of the yeast experiment, but what do these results mean?

Yeasts are microscopic, single-celled organisms, and are a type of fungus that is found all around us, in water, soil, on plants, on animals and in the air. Like all organisms, when yeasts are put in the right type of environment they will thrive; growing and reproducing.

Your experiments were designed to help you identify which environment promotes the most yeast growth. The first three glasses in your experiment contained different temperature environments (cold water, hot water and body temperature water). At very low temperatures the yeast simply does not grow but it is still alive – if the environment were to warm up a bit, it would gradually begin to grow. At very high temperatures the cells within the yeast become damaged beyond repair and even if the temperature of that environment cooled, the yeast would still be unable to grow. At optimum temperatures the yeast thrives.

Your third and fourth glasses both contained environments at optimum temperature (body temperature) for yeast growth, the difference being, the fourth glass was sealed. The variable between these two experiments was the amount of available oxygen. You may have been surprised by your results here, thinking that a living organism in an environment without oxygen cannot survive? However, you should have found that yeast grew pretty well in both experiments.

To understand why yeast was able to thrive in both conditions we need to understand the chemical process occurring in each glass during the experiment. In the three open glasses, oxygen is readily available, and from the moment you added the yeast to the sugar solution it began to chemically convert the sugar in the water and the oxygen in the air into energy, water, and carbon dioxide in a process called aerobic respiration.

Yeast is a slightly unusual organism – it is a ‘facultative anaerobe’. This means that in oxygen-free environments they can still survive. The yeast simply switches from aerobic respiration (requiring oxygen) to anaerobic respiration (not requiring oxygen) and converts its food without oxygen in a process known as fermentation. Due to the absence of oxygen, the waste products of this chemical reaction are different and this fermentation process results in carbon dioxide and ethanol.

Depending on how long you monitored your experiment for and how much space your yeast had to grow you may have noticed that, with time, the experiment sealed with cling film slowed down. This is for two reasons; firstly because less energy is produced by anaerobic respiration than by aerobic respiration and, secondly, because the ethanol produced is actually toxic to the yeast. As the ethanol concentration in the environment increases, the yeast cells begin to get damaged, slowing their growth.

The ethanol produced is a type of alcohol, so it is this process that allows us to use it to make beer and wine. When used in bread making, the yeast begins by respiring aerobically, the carbon dioxide from which makes the bread rise. Eventually the available oxygen is used up, and the yeast switches to anaerobic respiration producing alcohol and carbon dioxide instead. Do not worry though; this alcohol evaporates during the baking process, so you won’t get drunk at lunchtime from eating your sandwiches.

FREE K-12 standards-aligned STEM

curriculum for educators everywhere!

Find more at TeachEngineering.org .

• TeachEngineering
• Concentrate This! Sugar or Salt...

Hands-on Activity Concentrate This! Sugar or Salt...

Grade Level: 10 (9-12)

(four 55-minute sessions)

Expendable Cost/Group: US $3.00

Group Size: 2

Activity Dependency: None

Subject Areas: Algebra, Chemistry, Science and Technology

NGSS Performance Expectations:

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Engineering connection, learning objectives, materials list, worksheets and attachments, more curriculum like this, pre-req knowledge, introduction/motivation, vocabulary/definitions, troubleshooting tips, activity extensions, activity scaling, user comments & tips.

In the field of chemical engineering, it is important to understand the dependency of concentration on the physical properties of a liquid. Small changes (intentional and unintentional) in the composition of a liquid mixture can make dramatic changes to the liquid's boiling, melting or freezing point, density, viscosity or surface tension. Chemical engineers must understand how these changes can impact the function of a substance so they can account for, and design, new substances. For example, small changes can make the difference between your car starting in the winter or not, depending on whether or not the correct chemical composition of anti-freeze or motor oil was used.

After this activity, students should be able to:

• Follow step by step procedures to conduct an experiment.
• Apply the concept of concentration changes to alter boiling point.
• Correctly use units of concentration.
• Calculate solute mass from a known concentration and solvent mass.
• Determine when boiling occurs and measure a liquid's boiling point.
• Apply the understanding of boiling points and altering boiling points to a real-life engineering situation.
• Math competency: Skills and appreciation for data collection used in real life.
• Quantitative literacy: Ability to follow procedures and provide recommendations.
• Engineering applications: Engineering design process, material selection and cost considerations.
• Cultural relevancy: How to follow procedures, collaborative work in small groups and hands-on activities.

Educational Standards Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards. All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN) , a project of D2L (www.achievementstandards.org). In the ASN, standards are hierarchically structured: first by source; e.g. , by state; within source by type; e.g. , science or mathematics; within type by subtype, then by grade, etc .

Ngss: next generation science standards - science.

Common Core State Standards - Math

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International Technology and Engineering Educators Association - Technology

State standards, washington - math, washington - science.

Section 1- Boiling Point Data

Each group needs:

• beaker tongs or hot gloves
• 300 ml beaker
• thermometer
• burner or hotplate
• 200 ml water
• Section 1 Worksheet
• graduated cylinder
• glass stir rod
• aluminum foil (4" x 4" piece) used to form a lid over beaker during boiling

To share with the entire class:

• electronic balance (capable of weighing 200 ml water plus beaker weight)
• salt, approximately 250 g for every other group (each group only tests one solute)
• sugar, approximately 540 g for every other group (each group only tests one solute)

Section 2 - Data Analysis

• Section 2 Worksheet

Section 3 - Design

• Section 3 Worksheet
• salt, approximately 100 g per group
• sugar, approximately 180 g per group

Students should be familiar with:

• Math concepts: line graphs and fractions.
• Science concepts: concentration, mass, weighing practices, boiling point.

However, this activity could be used as a means of introducing some or all these concepts.

(The motivation for this activity is to familiarize students with concentrations by providing opportunities for them to first create solutions and calculate the concentration based on solute mass, test solutions for boiling point, then predict performance of other concentration based on data analysis, and then finally to calculate solute mass based on the needed concentration, and verify their prediction through testing boiling point of the new solution. Students also will understand the importance of determining the cost of a solution and relate this cost analysis to the engineering design process; engineers must optimize cost of materials in designs.)

How do chemical engineers design new materials and products in the lab? The method of test, analyze and validation is common practice in engineering. Today you will be doing the same thing. This gives you the opportunity to explore and understand data analysis in true lab situations where you must try to control as many variables as possible to produce the most accurate results.

What is the connection between chemistry and chemical engineering? (Listen to student ideas.) Chemical engineering is the application of a person's knowledge of chemicals, mixtures and solutions to solve real-world problems. What might be some examples? (Listen to student ideas.) There are so many examples. One example is that chemical engineers design specific anti-freeze and motor oil chemical solutions to help your car work more efficiently and effectively in specific conditions.

Before the Activity

• Gather materials.
• Make copies of Section 1 Worksheet , Section 2 Worksheet and Section 3 Worksheet.
• Test the salt and sugar concentrations to confirm the boiling point curves. Be sure to include the boiling point of the pure water sample.

With the Students

Before start of the lab:

Introduction to Solutions

• Discuss what makes a solution: a solvent plus a solute.
• Give examples of solutions and have students come up with their own examples (use Worksheet 1 to help guide this).
• Describe concentration as a means of describing (defining) a solution. Concentration is a measure of how much of some substance is contained in a mixture.
• Introduce units and decide which ones will be used in the labs.
• Introduce equation to calculate concentration based on masses of solute and solvent (use Worksheet 1 to help guide this).
• Discuss why concentration might be an important property of a mixture and how concentration may change other known properties (density, viscosity, surface tension, boiling point, freezing point). Specifically, use this information to introduce the concept of chemical engineering.
• Salt water fish tanks.
• Saline solutions used in hospitals.
• Why salt is put down on roads in the winter or why we make homemade ice cream by spreading salt on the ice. This is an example of engineering the defined environment- applying what engineers know about melting points and solutions to fix a real-world problem.
• Discuss how to use lab equipment.
• Review how to use and read a thermometer.
• Review how to use a balance and tare weights if necessary (ensure they are familiar with grams as opposed to ounces which sometimes appear on electronic balances).
• Introduce the definition of chemical engineering and describe real-life problems that chemical engineers might try to solve. Refer to the Introduction and Motivation section as an example.

Day 1: Section 1

• Hand out Section 1 Worksheet .
• Introduce the activity, engineering connection, and strategy for the four-day lab:

Day 1 : Section 1 Worksheet (definitions and determining boiling point of various solutions).

Day 2 : Section 2 Worksheet (data analysis and determining the best line of fit on a graph for various concentrations of salt and sugar).

Day 3 and 4 : Section 3 Worksheet (design and test a solution to have a specific boiling point based on previous calculations; connect this "design criteria" to what engineers must do, that is, meet specifications).

• Discuss results (if time at the end of class, once everyone is done).

Day 2: Section 2

• Hand out Section 2 Worksheet .

Day 3: Section 3

• Hand out Section 3 Worksheet .
• Discuss how students can calculate the solute mass necessary to achieve the required boiling point.
• Have students design their solutions and begin conducting the tests.

Day 4: Section 3 (continued)

• Report results and check solutions.

boiling point: The point at which one can see a steady/continuous/rapid boiling of a liquid. This point is also characterized by a constant temperature, as long as the concentration is not being changed.

concentration: A measure of how much of some substance is contained in a mixture.

solute: The material being dissolved in a solution, typically the material present in a lesser mass, and the material that is changing state. In this activity example, the salt and sugar are the solutes.

solution: A mixture of two or more substances. In this activity, salt water solution or sugar water solution.

solvent: The liquid substance able to dissolve other substances. In this activity, water is the solvent. The solvent does not change its state when forming a solution.

At activity end, review and grade completed student worksheets to gauge their mastery of the concepts.

Safety Issues

• Students should not drink any chemicals even those labeled water or soda because contamination is always possible.
• Students should always use safe lab practices especially when working with heat. Use tongs when handling hot containers and wear lab goggles to protect eyes.

Be sure to test the boiling point of the water that will be used. A deviation of a few degrees in boiling point may exist, depending on elevation and water supply.

Ensure that the thermometers being used are accurate and precise enough to capture half-degree changes in temperature. One option is to use digital thermometers. Also, ensure that the thermometer range covers the range of boiling points possible with the solutions (~212 °F to 240 °F).

During boiling, if water vapor (steam) is escaping from the beakers, it means the concentration inside the beaker is increasing due to a loss in solvent mass. To ensure the least error, encourage students to keep beakers completely covered. If possible, use rubber bands to secure the foil lids on the beakers.

To reinforce students' understanding of concentration, provide them with two or three unknown solutions for which they must determine the concentrations. Then, as an added challenge, challenge students to develop a method to determine if the unknown is a salt or sugar solution. This would be based on the mass of the solution as long as they are given the mass of the solvent.

Ask students to create concentration curves based on other measurable properties such as density. They could then compare to see if one measurement is a better predictor for determining an unknown.

Have students perform cost analysis of their solutions for section 3, comparing their group results to other group results.

• For lower grades, minimize testing to only one solute (salt) then have students collect data as a class. During section 3, have students calculate the cost to create the required boiling point solution.
• For upper grades, have students determine the effect each solute has on the boiling point error. For example, for a one-degree boiling point increase, it requires more sugar than salt. Therefore, the same precision of weighing results in a lower error associated with the sugar solution than the salt solution. Have students come up with methods to minimize these measurement errors. In addition, have students come up with an equation to determine the boiling point of a solution containing water + salt + sugar.

Students learn how to classify materials as mixtures, elements or compounds and identify the properties of each type. The concept of separation of mixtures is also introduced since nearly every element or compound is found naturally in an impure state such as a mixture of two or more substances, and...

Contributors

Supporting program, acknowledgements.

This content was developed by the Culturally Relevant Engineering Application in Mathematics (CREAM) Program in the Engineering Education Research Center, College of Engineering and Architecture at Washington State University under National Science Foundation GK-12 grant no. DGE 0538652. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.

Last modified: November 8, 2021

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• Open access
• Published: 22 April 2023

A unifying criterion of the boiling crisis

• Limiao Zhang 1 , 2 ,
• Chi Wang 1 , 3 ,
• Guanyu Su 1 , 4 ,
• Artyom Kossolapov   ORCID: orcid.org/0000-0003-4565-8423 1 ,
• Gustavo Matana Aguiar   ORCID: orcid.org/0000-0001-6561-8264 1 ,
• Jee Hyun Seong 1 , 5 ,
• Florian Chavagnat 1 ,
• Bren Phillips 1 ,
• Md Mahamudur Rahman   ORCID: orcid.org/0000-0003-3357-6922 1 , 6 &
• Matteo Bucci   ORCID: orcid.org/0000-0002-6423-1356 1  

Nature Communications volume  14 , Article number:  2321 ( 2023 ) Cite this article

• Fluid dynamics
• Mechanical engineering

We reveal and justify, both theoretically and experimentally, the existence of a unifying criterion of the boiling crisis. This criterion emerges from an instability in the near-wall interactions of bubbles, which can be described as a percolation process driven by three fundamental boiling parameters: nucleation site density, average bubble footprint radius and product of average bubble growth time and detachment frequency. Our analysis suggests that the boiling crisis occurs on a well-defined critical surface in the multidimensional space of these parameters. Our experiments confirm the existence of this unifying criterion for a wide variety of boiling surface geometries and textures, two boiling regimes (pool and flow boiling) and two fluids (water and liquid nitrogen). This criterion constitutes a simple mechanistic rule to predict the boiling crisis, also providing a guiding principle for designing boiling surfaces that would maximize the nucleate boiling performance.

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Introduction.

The importance of boiling cannot be overstated. Boiling is crucial to the operation, efficiency and safety of technologies (e.g., electric energy production, sterilization, water desalination, power electronics, medical diagnosis and therapy, fission and fusion energy, high-performance computing, space exploration and colonization) that are critical to the present and future of humankind.

Nucleate boiling (i.e., boiling via the nucleation of bubbles at a heated surface) is an effective heat removal process. The amount of energy required to transform liquid into vapor and grow a bubble is typically large compared to the energy necessary to increase the liquid temperature, e.g., from ambient temperature to its boiling point 1 , 2 . This energy is provided by the surface from which heat is to be removed, e.g., the cladding of a nuclear reactor fuel rod, where bubbles nucleate at discrete locations called nucleation sites. The heat flux that can be removed by nucleate boiling depends on nucleation sites area density (simply called nucleation site density), bubble size and release frequency. When, starting from a stable operating condition (see Fig.  1a ), the heat flux to be removed from the heated surface is increased, the process finds a new point of equilibrium by self-adjusting these parameters (e.g., by increasing the nucleation site density). However, at high heat fluxes, this process may become unstable. When that happens, the heated surface suddenly gets covered by a stable vapor film (see Fig.  1b ). This instability, known as a boiling crisis, is a key operational limit in many systems, e.g., nuclear reactors, as this vapor film has poor heat transfer properties 3 (see Fig.  1d ). Thus, when the boiling crisis occurs, the surface temperature (see Fig.  1e ) may suddenly increase up to the point where the surface burns out (see Fig.  1c ) or even melts, causing the system’s failure.

a High-speed video image of the nucleate boiling process. b High-speed video image of the film boiling process (on the same surface as a ). a and b show examples obtained in flow boiling conditions on a vertical surface. c Picture of a burnt-out surface which experienced the boiling crisis. This burnout may be followed by the melting of the surface. d Heat flux distribution on a boiling surface experiencing film boiling. e Temperature distribution on a boiling surface experiencing film boiling. d and e are simultaneous measurements obtained using infrared thermometry and have the same scale bar. The large patch with poor heat transfer properties (zero heat flux in d ) and high temperature (hot spot in e ) indicate the presence of a stable vapor film covering the heated surface.

The boiling crisis is a century-old scientific problem. For years, it has been viewed as the outcome of a hydrodynamic instability occurring far from the heated surface 4 . When the release frequency of bubbles from nucleation sites is too high, bubbles merge to form vapor columns. The flow of vapor within these columns increases with the heat flux. However, there is a critical vapor velocity, above which these vapor columns deform due to Helmholtz instabilities and merge, obstructing the flow of liquid towards the heated surface, which eventually dries out. Antithetical descriptions consider the boiling crisis as a near-wall instability related to the characteristic of the nucleate boiling process at the heated surface. For instance, it has been suggested that the boiling crisis is the consequence of a mechanical unbalance of the liquid-vapor-solid contact line, triggered by the recoil forces that generate when the near-wall liquid vaporizes 5 , 6 , 7 , 8 . In some models, the boiling crisis is thought of as a consequence of a critical packing of bubble on the heated surface, due to an increase of the nucleation site density 9 . In some other models, the key to predicting the boiling crisis is the bubble growth time, i.e., the time a bubble takes to grow and leave the heated surface. The bubble growth time determines the rise of surface temperature during the bubble life cycle, which is the critical parameter in some models 10 , 11 , 12 . Decreasing the bubble growth time is beneficial, as it reduces the temperature rise. It is also beneficial because it increases the bubble release frequency and, consequently, the heat flux that can be removed by the nucleate boiling process 13 . However different, all these models have a common denominator: they all assume that the boiling crisis can be predicted as the outcome of a phenomenon triggered by a single critical characteristic quantity, e.g., the vapor velocity in the vapor columns or the nucleation site density or the growth time. As models often come from empirical observations of the boiling process in different operating conditions or on surfaces with different physicochemical properties, the diversity and specificity of these models may indicate that there is not a unique triggering mechanism of the boiling crisis, or that we still have not found the central idea that reconciles all these observations.

Here, we prove the existence of a criterion that captures the boiling crisis over a broad range of surface and operating conditions by unifying into a single paradigm the synergistic and intertwined effect of the length and time scales involved in the boiling process (i.e., nucleation site density, average bubble footprint size, growth time and departure frequency).

We have recently discovered the signature of the boiling crisis in the probability density function of the bubble footprint areas on the heated surface 14 , 15 . This discovery has been possible through experiments (see examples of subcooled flow boiling results on a rough zirconium surface in Fig.  2 ) featuring high-resolution optical diagnostics (e.g., infrared thermometry 16 and phase detection 17 ) developed in-house (see Methods ), which enable detection of bubble footprints and other boiling parameters (e.g., bubble footprint area distributions, circular-equivalent footprint radius distribution of non-interacting bubbles, bubble growth time and detachment frequency, and nucleation site density). We observed that, for low heat fluxes, when there are only a few bubbles growing on the boiling surface (e.g., see Fig.  2 b, c at 0.79 MW/m 2 in the example of the figure), the bubbles do not interact with each other, and their footprint area distribution is a damped function with a proper mean value and standard deviation (i.e., discrete bubbles have, as expected, a proper length scale). As the heat flux is increased and more bubbles grow on the surface, they start to interact occasionally forming larger vapor patches (e.g., see Fig.  2c at 2.36 MW/m 2 in the example of the figure). Upon occurrence of the boiling crisis (see Fig.  2 b, c at 3.48 MW/m 2 in the example of the figure), this distribution follows a scale-free trend, i.e., a power-law distribution with a negative exponent <3. The occurrence of a scale-free distribution has profound implications. Its standard deviation is infinite. As such, it is not possible to define this distribution by means of a dominant, central value, such as for a normal distribution. Instead, all scales are equally important. This observation inspired us to recognize the importance of seldom, large fluctuations of the bubble footprint area in triggering the boiling crisis and to realize that, to fully understand and predict the boiling crisis, one cannot only focus on the behavior of a single bubble, but needs to look at how bubbles behave collectively, at all scales. Describing their interaction correctly and predicting these bubble footprint fluctuations is the key to predicting the boiling crisis.

a Sketch of the experimental apparatus and high-resolution camera for infrared thermometry or phase-detection measurements. b Experimental boiling curve. c Experimental bubble footprint area distributions. d Example of the stochastic bubble interaction model output. e Bubble footprint distributions predicted by the stochastic model. f Evolution of the giant (G) and second giant (SG) bubble clusters with heat flux predicted by the model, showing that a power law bubble footprint area distribution coincides with a bifurcation of the G and SG clusters area.

We have captured this behavior by modeling the bubble interaction as a stochastic continuum percolation process (see Fig.  2d and Methods or Refs. 14 , 15 for the details of the model), driven by three fundamental boiling parameters: nucleation site density \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , average footprint radius \(R\) of non-interacting bubbles and product of average bubble growth time \(\,{t}_{{{{{{\rm{g}}}}}}}\) and detachment frequency \(f\) , which expresses the probability to have a bubble growing at a nucleation site (note that this probability is between 0 and 1, as \(f=1/({t}_{{{{{{\rm{g}}}}}}}+{t}_{{{{{{\rm{w}}}}}}})\) , where \({t}_{{{{{{\rm{w}}}}}}}\) is the time elapsed from the departure of a bubble until the nucleation of a new one from the same nucleation site). This model predicts how the experimental bubble footprint area distribution changes with the heat flux through the aforesaid (measured) boiling parameters (see Fig.  2e ). It confirms that, at the boiling crisis, the bubble footprint area distribution is scale-free. Importantly, it reveals that the boiling crisis (i.e., the power-law distribution) coincides with a bifurcation. Figure  2f shows how the area of the most likely giant (G) and second giant (SG) bubble cluster (i.e., the bubble clusters with the largest and second largest footprint area, respectively) changes with the heat flux. In nucleate boiling (i.e., for heat fluxes below 3.48 MW/m 2 for in the example of Fig.  2f ), the size of these clusters is comparable and grows monotonically. However, if, starting from the critical distribution (i.e., 3.48 MW/m 2 in the example of Fig.  2 ), one increases \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , or the average footprint radius \(R\) , or the product \(f{t}_{{{{{{\rm{g}}}}}}}\) , i.e., if one increases the heat flux, the model intrinsically predicts that all the bubble clusters suddenly merge together into a unique giant vapor patch (see Fig.  2f ). This behavior is confirmed by the prediction of a supercritical bubble footprint area distribution (see Fig.  2e ). In other words, the model predicts a sudden transition from a nucleate boiling regime to a stable vapor film, called film boiling regime (see Fig.  2b ). This analysis suggests that the boiling crisis is triggered by an instability in the bubble interaction process, which occurs for a critical combination of \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , \(R\) , and \(f{t}_{{{{{{\rm{g}}}}}}}\) , i.e., a critical triplet.

Ideally, critical, scale-free distributions can be obtained with infinite combinations of these three parameters, i.e., there is an infinite number of critical triplets. Such triplets can be identified using the stochastic model. Consider the case where average footprint radius of non-interacting bubbles, growth time and departure frequency are fixed, and the nucleation site density progressively increases starting from a value for which bubbles are sparse and do not interact with each other. In these conditions, the bubble footprint area distribution follows a damped function (i.e., the footprint area distribution of non-interacting bubbles). As the nucleation site increases, this distribution changes, until for a certain value of the nucleation site density, this distribution becomes scale free. Starting from this distribution, a further addition of nucleation sites would result in the presence of a unique vapor cluster on the boiling surface (i.e., the film boiling regime). The bifurcation in the G and SG cluster size (as same observed in Fig.  2f ) can be used to identify the critical triplet. This modeling exercise can be repeated by changing the initial \(R\) , or \(f\,{t}_{{{{{{\rm{g}}}}}}}\) , or, in general, by keeping any of the parameters fixed except one. By doing so, we could identify a wide number of critical triplets. Notably, they are described by a simple non-dimensional formula (see Fig.  3a ):

Here, \(C\) depends on the non-dimensional boiling area \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}\,{R}^{2}\) (where \({A}_{{{{{{\rm{h}}}}}}}\) is the area of the boiling surface). It increases from 0.95, for a nondimensional area of 10, to an asymptotic value of 1.15 for a non-dimensional area of 10000 or larger (see Methods ). In the typical range of non-dimensional boiling area of literature experiments, including ours (mostly between 50 and 300), the average \(C\) value is 1.03 with a standard deviation \({{{{{{\rm{\sigma }}}}}}}_{C}=0.06\) . Note that \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\,{{{{{\rm{\pi }}}}}}\,{R}^{2}\) is the area fraction that would be covered by bubble, if they were not interacting, and \(f{t}_{{{{{{\rm{g}}}}}}}\) is the probability that a bubble exists. We could be tempted to think that the boiling crisis (i.e., \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}\,{R}^{2}f{t}_{{{{{{\rm{g}}}}}}} \sim 1\) ) occurs when bubbles cover, on average, the entire heated surface—a mental picture that recall the image drawn in the early work of Rohsenow and Griffith 9 . However, Eq. ( 1 ) does not imply that the entire surface is simultaneously covered by bubbles. In fact, even in critical conditions, only fraction of the surface (typically between 40% and 60%) is covered by bubbles simultaneously.

a Critical surface determined using the stochastic model. b Representation of the experimental boiling triplets ( \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}},\,R,\,f{t}_{{{{{{\rm{g}}}}}}}\) ) for several boiling surfaces and operating conditions (Source data are provided as a Source Data file). The dot grayscale is proportional to the ratio between the heat flux and the maximum heat flux that each surface (represented by different line colors) can remove in nucleate boiling. White dots indicate the experimental boiling crisis and lie on the theoretical critical surface \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}{{R}}^{2}f{t}_{{{{{{\rm{g}}}}}}}=1.03\) . c Simplified view of the critical surface (dashed line) and the experimental boiling triplets ( \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}},\,R,\,f{t}_{{{{{{\rm{g}}}}}}}\) ) at the boiling crisis for all surfaces and operating conditions. Solid lines represent the standard deviation on the theoretical critical constant (see Methods). An illustration of the effects of measurement uncertainties is shown in the Methods section.

The theoretical scaling expressed by Eq. ( 1 ) is a criterion of the boiling crisis. It defines the criticality boundary between a stable and efficient nucleate boiling regime, and a stable but inefficient film boiling regime. To verify this criterion, we conducted experiments in a broad range of operating and surface texture conditions. These experiments feature high resolution optical techniques to image the boiling surface and measure the time-dependent distributions of the temperature and heat flux, or the phase (liquid or vapor) distributions in contact with the boiling surface (see Methods). From these measurements, we can quantify the number of nucleation sites (i.e., the nucleation site density, \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) ), the circular-equivalent footprint radius distribution of discrete, non-interacting bubbles, \({{{{{\rm{p}}}}}}(r)\) , as well as the bubble growth time \({t}_{{{{{{\rm{g}}}}}}}\) and the bubble departure frequency \(f\) on any kinds of surface we tested (see Methods for the details). We investigated the pool boiling of saturated water at atmospheric pressure on nano-smooth indium tin oxide (ITO), nano-smooth chromium, nano-smooth alumina, copper oxides nano-leaves, zinc-oxide nanowires, and coatings made of silicon dioxide nanoparticles. We also investigated the pool boiling of liquid nitrogen at atmospheric pressure on ITO, and the flow boiling of water at atmospheric pressure with 10 K of subcooling on ITO, zinc-oxide nanowires, coatings made of silicon dioxide nanoparticles, and a rough Zirconium surface. These surfaces and operating conditions (summarized in Tables  1 and 2 ) were selected to cover a broad range of boiling triplets (at the boiling crisis, the \(f{t}_{{{{{{\rm{g}}}}}}}\) values range between 0.28 and 0.53, the \(R\) values between 0.17 and 0.61 mm, and the \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) values between 222 and 2195 sites per cm 2 ). Figure  3b shows values of the experimental boiling triplets for all the surfaces and operating conditions we tested. The line color of each dot indicates a specific surface and operating conditions. Instead, the dot grayscale intensity for each series of data is proportional to the ratio between the heat flux and the maximum nucleate boiling heat flux that could be removed by the selected surface and operating condition (also known as critical heat flux or CHF). In general, experimental triplets are located at the left of the critical surface, i.e., their \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}\,{R}^{2}f{t}_{{{{{{\rm{g}}}}}}}\) product is <1.03. However, the last (and brightest) point of these experimental three-dimensional boiling curves (i.e., the point at which the boiling crisis occurs) lies on top of the critical boundary defined by Eq. ( 1 ) (see Fig.  3c for a clearer representation and the Methods section for an illustration of the effects of measurement uncertainties). In other words, the boiling crisis happens when the non-dimensional boiling crisis number \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}\,{R}^{2}f{t}_{{{{{{\rm{g}}}}}}}\) calculated with the measured boiling triplet becomes 1.03, no matter the boiling surface or operating condition. We emphasize that, while we did not test hydrophobic surfaces with static contact angles much >90°, our paradigm contemplates all surface conditions and, possibly, heater geometry effects. For instance, on hydrophobic surface, depending on nucleation sites size distribution and nucleation temperature, the boiling crisis may occur with a large number of small bubbles (i.e., with a small footprint) and a short wait time (i.e., a high \(f{t}_{{{{{{\rm{g}}}}}}}\) ) 18 . In some other cases, the bubble departure diameter on hydrophobic surfaces may be significantly higher than on hydrophilic surfaces 19 , and the boiling crisis may happen with a combination of large bubble footprint radius and smaller nucleation site density (and likely higher \(f{t}_{{{{{{\rm{g}}}}}}}\) product). However, while experiments on superhydrophobic surfaces and considering other effects (e.g., heater size and lateral confinement) may be run in the future, the critical condition expressed by Eq. ( 1 ) should not change.

Last but not least, while Eq. ( 1 ) contemplates any surface conditions and bubble dynamics, it also yields the same scaling of the critical heat flux (CHF) with the physical properties of the fluid (and operating conditions) predicted by the Kutateladze-Zuber correlation 4 (see Methods). At the same time, our idea corroborates the hypothesis that the boiling crisis is a near-wall phenomenon, as we only used information related to the dynamic of bubbles at the heating surface. Interestingly, the concurrence of these observations suggest that our idea can reconcile far-field and near-wall views of the boiling crisis.

In summary, we prove with a theoretical and experimental investigation the existence of a unifying scaling criterion of the boiling crisis. This non-dimensional criterion was postulated through a stochastic continuum percolation model of the bubble interaction process, which captures large-scale bubble cluster fluctuations and predicts the boiling crisis as an instability of the bubble interaction process. Experimental data for a variety of surfaces, operating conditions and fluids confirm this theoretical unifying scaling criterion. We emphasize that, in this context, the word unifying is used because this criterion combines and captures the synergistic and intertwined effect of the length and time scales involved in the boiling process, i.e., nucleation site density, bubble size, growth time and departure frequency.

Equation ( 1 ) provides a simple mechanistic criterion to model the boiling crisis in advanced two-phase heat transfer computational tools used for the design of industrial and scientific systems, where it can be used in combination with heat flux partitioning approaches to predict the critical heat flux 15 . It also constitutes a guiding principle for designing boiling surfaces that would maximize the nucleate boiling performance, e.g., by engineering surface features that maximize the heat flux that can be removed by critical triplets.

Experimental methodology

We conduct pool and flow boiling experiments using special heaters, enabling the use of high-speed infrared (IR) thermometry to measure the time-dependent infrared radiation distribution emitted by the boiling surface. This technique is used in all the experiments with de-ionized (DI) water. Instead, we run experiments with liquid nitrogen (LN2) using a different optical technique called phase detection.

Experiments with water

Boiling experiments with water are conducted using special infrared heaters, designed and built in-house. They consist of a 1 mm thick sapphire substrate (20 × 20 mm 2 ), coated on one side with a thin electrically conductive film, which is the actual Joule heating element (see Fig.  4c ). This film can be made of Indium Tin Oxide (ITO) or metals, and it is less than a micron thick. It is connected to a power supply with two silver or gold pads with negligible electrical resistance, which define the active heating area (nominally 10 × 10 mm 2 ). This heater is installed at the bottom of our pool boiling facility or on the side wall of our flow loop, with the thin electrically conductive film in contact with water. We emphasize that the thermal response of the heaters used in this study is not determined by the thin heating layer, but rather by the underlying 1 mm thick sapphire substrate, which has a large thermal capacity. Importantly, sapphire has thermal properties (e.g., diffusivity and effusivity) very similar to stainless steel, Inconel and zircaloy, which are materials of interest for commercial boiling applications, e.g., in nuclear reactor fuel claddings.

a Cross sectional view of the pool boiling apparatus used for boiling experiments with water. b Cross sectional view of the flow boiling apparatus used for boiling experiments with water. c Sketch of the infrared heater (not to scale). d Examples of instantaneous infrared radiation distribution (left) and the resulting temperature (middle) and heat flux distributions (right). e Nucleation probability map (in arbitrary units) with the identified nucleation sites (left), and example of temperature (middle) and heat flux (right) time-evolution at a selected nucleation site throughout a bubble life cycle.

The pool boiling facility (see Fig.  4a ) consists of a concentric double cylinder structure, forming two separate fluid cells. The working fluid, DI water, is in the inner cell. A temperature-controlled oil is circulated throughout the outer cell, which is surrounded by an insulating material to minimize heat losses to the environment (this insulating material is not shown in the sketch of Fig.  4a ). The external cell works as an isothermal bath and is used to bring the DI water to and maintain it at the desired temperature. The temperature of the two fluids (oil and DI water) is monitored using T-type thermocouples installed in both cells. The free surface of the water is 15 cm above the heater. The latter is accommodated over a ceramic support structure sitting on the bottom of the inner cell. The inner cell of the apparatus is abundantly rinsed with DI water before the beginning of each experiment. Then, the heater is installed, and the cell is filled with DI water at room temperature. At this point, the temperature of the oil in the outer bath is gradually increased until the temperature of the DI water in the inner cell reaches saturation temperature. As the saturation temperature is reached, we leave the apparatus to thermalize for ~30 min. During this phase, we turn the heater power on for ~10 min to induce nucleate boiling and degas the heater surface as well. All the pool boiling experiments presented in this paper are conducted at atmospheric pressure.

The flow boiling facility (see Fig.  4b ) consists of a stainless steel 316 L test section with a 3 cm × 1 cm flow channel running the length of the structure. It connects to an entrance region (not shown in Fig.  4b ) over 60 hydraulic diameters long to establish fully-developed turbulent flow at the position of the heater. The main body of the test section consists of four sides. Three are used for quartz windows to provide optical access; the fourth wall contains a ceramic cartridge used to hold the IR heater perfectly flushed with the channel walls. The facility is equipped with variable frequency pump, flow meter, temperature and pressure instrumentation, preheater, chiller, accumulator, and a fill-and-drain tank. Filtering and dissolved oxygen monitoring is accomplished via a secondary loop used during the initial stages of testing. A pump provides the head required for the desired mass flux, i.e., 1000 kg/m 2 s in these experiments. The bulk temperature of the fluid is controlled by adjusting the power of the preheater and the secondary flow in the chiller. The experiments discussed in this paper are run at atmospheric pressure with slightly subcooled water at 90 °C.

As we circulate current through the electrically conductive film of the heater, it releases the heat necessary to warm up the sapphire substrate and boil the water by Joule effect. Importantly, this electrically conductive film has negligible thermal capacity and thermal resistance. Thus, its temperature coincides with the temperature at the interface between the solid and the fluid, i.e., the boiling surface temperature. Noteworthy, while sapphire is quasi-transparent to infrared radiation in the 3–5 µm range, this film is perfectly IR opaque. It emits time-dependent and space-dependent radiation proportional to its temperature. We use an infrared camera (IRC806HS) to record the radiation emitted by the entire heater (i.e., nominally 10 × 10 mm 2 ) at a temporal resolution of 2500 frames per second (i.e., with a time step of 0.4 ms) and a pixel resolution of 115 µm. We have developed a calibration technique to convert this time-dependent radiation distribution into temperature and heat flux. The quasi-transparent (but not perfectly transparent) nature of the sapphire makes this process complicated. Sapphire partially absorbs and emits radiation with a wavelength >4 µm, contaminating the radiation signal emitted by the thin heating film, which is the one we need to measure. Reflections of the background radiation further contaminate this signal. The radiation emitted by the thin heating film is found through the solution of an inverse problem coupling optical radiation and conduction heat transfer in the substrate. For more details, we direct the reader to our previous work 16 . Using this calibration technique, we obtain the time-dependent distributions of boiling surface temperature, \({T}_{{{{{{\rm{w}}}}}}}(x,\,y,\,t)\) , and heat flux from the thin heating film to the sapphire substrate, \({q}_{{{{{{\rm{s}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}(x,\, y,\, t)\) . The time-dependent distribution of the heat flux to water, \({q}_{{{{{{\rm{w}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\left(x,\,y,\,t\right)\) , is obtained as the difference between the Joule heating superficial power density and the heat flux to sapphire. Precisely, the Joule heating superficial power density, \({q}_{{{{{{\rm{h}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , is measured as the product of the current circulating through the heater, \(I\) , and the voltage drop across the silver pads, \(V\) , divided by the actual heating area, \({A}_{{{{{{\rm{h}}}}}}}\) .

The time-dependent distribution of the heat flux to water is eventually obtained as

During the experiments, the heat flux is increased in steps, until the boiling crisis occurs. For each heat flux step, we record the infrared radiation emitted by the heater for 2 s. The time-dependent infrared radiation distributions can be post-processed to obtain the time-dependent temperature and heat flux distributions according to the technique introduced before and discussed in detail in our previous work 16 . Figure  4d shows an example of instantaneous infrared radiation and the associated temperature and heat flux distributions.

These time-dependent distributions can be analyzed to extract fundamental boiling parameters, e.g., nucleation site density, bubble growth time, bubble period, and, accordingly, bubble departure frequency, and bubble footprint size distributions. This postprocessing requires several image segmentation techniques, whose details are extensively discussed in a previous communication 20 . In brief, the detection of nucleation sites is obtained as follows. A nucleation event produces a peak in the heat flux distribution, \({q}_{{{{{{\rm{w}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\left(x,\,y,\,t\right)\) . A dry spot grows underneath the bubble as the micro-layer evaporates around it, which leads to a local drop in the heat flux. Based on this observation, nucleation sites coincide with peaks in the measured probability scalar field, \({{{{{{\rm{p}}}}}}}_{{{{{{\rm{n}}}}}}}\) , calculated as

where \({{{{{\rm{f}}}}}}\) is the frame index and \({N}_{{{{{{\rm{f}}}}}}}\) is the number of frames (typically 5000 for 2 s). Note that the logical operators give 1 when the condition is satisfied and 0 if it is not. A sample probability map is shown in Fig.  4e . The nucleation sites are automatically detected as the peaks of the \({p}_{{{{{{\rm{n}}}}}}}\) distribution. However, we always conduct a thorough visual check of the time-dependent temperature and heat flux distributions that may result in the removal or addition of nucleation sites. Once the nucleation sites are identified, the nucleation site density \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) is obtained as the ratio between the number of nucleation sites \({N}_{{{{{{\rm{s}}}}}}}\) and the active heating area \({A}_{{{{{{\rm{h}}}}}}}\) . Then, the average bubble growth and wait time are identified for each of the nucleation sites, by analyzing the variation in temperature and heat flux (See Fig.  4e ). For a given nucleation site, a nucleation event coincides with a sharp peak in the heat flux evolution (point 1 to 2 in the right figure), or a temperature drop (point 1 to 2 in the middle figure). As a dry spot forms underneath the bubble (after point 2), the heat flux drops suddenly, and the wall temperature starts increasing (points 2 through 3). As the bubble departs from its nucleation site, cold liquid quenches the site causing a second heat transfer peak associated with a wall temperature drop (point 4). Then, a new thermal boundary layer grows in the liquid until a new nucleation event occurs. The bubble period, \({t}_{{{{{{\rm{b}}}}}}}\) , is measured as the distance between two nucleation events (point 1 to 1'), the reciprocal of which gives the bubble departure frequency, \(f\) . The bubble growth time, \({t}_{{{{{{\rm{g}}}}}}}\) , is measured as the difference between the bubble period and the bubble wait time, \({t}_{{{{{{\rm{w}}}}}}}\) . Average quantities are obtained by tracking every nucleation event at each of the nucleation sites. They are calculated as

where \(\alpha\) is the variable of interest (e.g., \(f{t}_{{{{{{\rm{g}}}}}}}\) ), \({N}_{{{{{{\rm{s}}}}}}}\) is the number of nucleation sites, and \({N}_{{{{{{\rm{e}}}}}},{{{{{\rm{s}}}}}}}\) is the number of events for the \({{{{{\rm{s}}}}}}\) -th nucleation site. The bubble footprint area distribution is determined by segmenting the images to distinguish the bubble footprint from the rest of the working fluid. The details of the image segmentation process are described in a previous communication 20 . This process also allows to separate discrete, non-interacting bubbles, i.e., bubbles that nucleate and depart from the surface without merging other bubbles. The footprint area distribution of non-interacting bubbles is found to be an exponential decay function 14 :

where \({{{{{\rm{c}}}}}}\) is obtained by fitting the measured distribution. Assuming that the footprint of isolated bubbles is circular (i.e., \(A={{{{{\rm{\pi }}}}}}\,{r}^{2}\) ), the corresponding equivalent radius distribution is given by

We can analytically demonstrate that the average value of this distribution, i.e., the average bubble footprint radius, \(R\) , is related to \(c\) :

Thus, the bubble footprint radius distribution can be written as:

Equation ( 9 ) is used to sample the size of bubble footprint in the stochastic model, and it is uniquely defined once the average footprint radius \(R\) is given.

Boiling surfaces used for the water experiments

We test seven different boiling surfaces:

a plain ITO surface;

a plain chromium (Cr) surface;

a plain Alumina surface;

a plain copper surface covered by copper oxide (CuO) nanoleaves;

a plain titanium surface covered by zinc oxide (ZnO) nanowires;

a plain ITO surface covered by a porous layer of silicon dioxide (SiO 2 ) nanoparticles;

a rough zirconium (Zr) surface;

All surfaces are fabricated on the sapphire substrate described before. The ITO, Cr, and Alumina surfaces are deposited directly on the sapphire substrate by sputtering using a PRO Line PVD 75 by Kurt J. Lesker. Zinc oxide nanowires are created following the process described by Ko et al. 21 . Copper oxide nanoleaves are chemically etched following the same process as Rahman et al. 22 . The porous layer of silicon dioxide nanoparticles is coated using the layer-by-layer procedure developed by Lee et al. 23 . The rough Zr surface is fabricated according to the process described by Su et al. 15 . The ITO, Alumina, Cr and rough Zr surfaces have a contact angle with DI water of ~85°, 10°, 29° and 47° respectively (measured with an optical goniometer in air). However, all other surfaces (CuO nanoleaves, ZnO nanowires and SiO 2 nanoparticles) are super-hydrophilic. The apparent contact angle on these surfaces is 0, as a liquid droplet would be rapidly absorbed by the super-hydrophilic structures. The parameter used to characterize this super-hydrophilicity is the so-called wicking number. The wicking number, Wi, of these surfaces has been measured using the same definition and protocol proposed by Rahman et al. 24 . Fig.  5h summarizes the measured contact angle and wicking number, together with the surface roughness. Scanning Electron Microscope images of these surfaces are also shown in Fig.  5 .

a ITO. b Silicon dioxide nanoparticles. c Zinc oxide nanowires. d Alumina. e Copper oxide nanoleaves. f Rough zirconium. g Chromium. h Schematic of the heater and measured roughness, wicking number, and contact angle for the tested surfaces.

Experiments with liquid nitrogen

The pool boiling experiment with liquid nitrogen is run with a specific setup, due to the peculiar behavior and boiling temperature of cryogenic fluids. Liquid nitrogen is boiled at the bottom of a thermally-insulated boiling cell by energizing a heating element (see Fig.  6a ). The heater is the same as the ITO coated sapphire substrate used for the water tests. The boiling cell consists of a 7.6 cm side cube of aluminum, with a cartridge inserted on its bottom side and supporting the heater. The cartridge is made of low-thermal conductivity resin to reduce parasitic heat leaks. The boiling cell is filled with industrial-grade liquid nitrogen from a Dewar. The ITO is in direct contact with the liquid nitrogen and oriented horizontally upward. The cell is placed inside of a moisture-free chamber to prevent frosting on the optical windows and on the sapphire substrate. The chamber has tubing ports for filling with moisture-free nitrogen gas as well as liquid/gas nitrogen and electrical feedthroughs for the operation of the boiling cell. The nitrogen gas formed by boiling is directly evacuated to the atmosphere, and the boiling cell is regularly refilled with liquid nitrogen to keep the fluid level at 7 cm above the heating surface.

a Cross sectional view of the pool boiling apparatus used for boiling experiments with liquid nitrogen. b Illustration of the phase-detection technique.

The cryogenic boiling experiment is performed at ambient pressure and saturated condition, same as the DI water experiments. At atmospheric pressure, the liquid nitrogen saturation temperature (i.e., −195.8 °C) is too low for measuring the temperature of the ITO using the infrared thermometry techniques. We also avoided the use of thermocouples due to the parasitic heat leak they can induce in the metallic sheath. Instead, we developed in-house a thin-film resistance thermometer (RTD). The RTD consists of a 500 nm-thick thin film of chromium oxide coated on the back side of the sapphire substrate (i.e., facing the moisture-free chamber). By tuning the content of oxygen inside the chromium oxide, the thin-film is made to behave as a semi-conductor, whose resistivity varies appreciably with its temperature. The RTD is driven by a 1 mA current generating a negligible heating power in the substrate (i.e., below 2 mW), and the voltage across the sensor is measured using a 4-point probe technique. The temperature of the RTD is obtained from the voltage across the RTD and by linear interpolation between 2 reference points. We use the saturation temperature of liquid nitrogen and liquid argon (i.e., −186.0 °C) as reference points. The thermal conductivity of sapphire reaches values as high as 1200 W/m/K at the boiling temperature of liquid nitrogen. With this thermal conductivity, we can safely assume that the substrate is isothermal and thus the temperature measured by the RTD is also the temperature of the boiling surface. The space-averaged heat flux to the fluid is simply given by the Joule heating superficial power density, \({q}_{{{{{{\rm{h}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) . In order to capture the boiling dynamics and quantify the desired boiling parameters, the cryogenic pool boiling experiment is equipped with an optical setup allowing us to perform phase detection measurements. This technique allows tracking the phase (i.e., liquid and gaseous nitrogen) in contact with the heating surface (i.e., ITO) during boiling. The measurement method works on the principle of partial internal reflection of an incoherent quasi-monochromatic colored LED light at the ITO—nitrogen interface. With this technique we can track the bubble footprints and more generally, the position of the triple contact lines. This method was developed by Kossolapov et al. and applied to DI water 17 . Figure  6b shows a schematic of the optical setup as well as the typical raw image of the liquid nitrogen boiling process recorded by a high-speed video camera. A quasi-monochromatic red LED light beam is shined from the back side of the substrate with an incidence angle of 20° with the heating surface normal. The amount of light reflected depends on the index of refraction of the fluid in contact with the ITO. Gaseous nitrogen has an index of refraction much more different than liquid nitrogen from the index of refraction of sapphire. Thus, gaseous nitrogen reflects more light than liquid nitrogen. The reflected light is then captured by a high-speed video camera, producing contrasted gray images with bright and dark indicating gas and liquid nitrogen in contact with the heated surface, respectively. Our light source is a quasi-monochromatic LED with a spectrum centered around 620 nm. We use a high-speed video camera (Phantom v2512) with a temporal resolution of 30,000 frames per seconds and a pixel resolution of 5.4 µm. This is sufficient to resolve the length and time scales of the boiling process even with cryogenic fluids. Raw phase-detection images (such as the one shown in Fig.  6b ) are post-processed to facilitate the measurements of the boiling parameters of interest. The post-processing of the raw images consists of a background removal followed by few steps of filtering to eliminate potential artefacts, such as dust on the optical setup. The boiling parameters of interest (i.e., nucleation site density \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , product of the nucleation frequency by the growth time \(f{t}_{{{{{{\rm{g}}}}}}}\) , average radius \(R\) of discrete bubbles, and overall bubble footprint area distributions) can be measured from the post-processed phase-detection recordings. The measurement of \(R\) and \(f{t}_{{{{{{\rm{g}}}}}}}\) requires isolating each bubble in order to characterize them individually. The post-processed recordings are binarized and segmented, allowing us to identify each individual bubbles and all bubble clusters. The methodology used to evaluate each boiling parameter is briefly described hereafter. \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) is evaluated by tracking manually, on each recording, the position from where bubbles nucleate. The distinct positions, i.e., the active nucleation sites, are counted, and the total is divided by the surface area. Bubbles cannot be observed exactly at the moment of nucleation, but when they reach a sufficient size (typ., about 3–5 pixels). Therefore, 2 seemingly distinct positions of nucleation may be misinterpreted as separate nucleation sites. To avoid an overestimation of \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , 2 close-enough reported positions are considered as a single nucleation site. \(R\) is evaluated by calculating the surface area of each bubble and clusters from the binarized recordings and for each frame. For high heat flux, typically close to CHF, very large clusters are excluded from the evaluation of \(R\) . The exclusion threshold is empirically defined by the cluster whose surface area is larger than the 99th percentile of the size of all clusters. For each nucleation site, the site-wise \(f{t}_{{{{{{\rm{g}}}}}}}\) is evaluated as the fraction of time that the nucleation site is covered by vapor. It is obtained by averaging in time all binarized images from the same recording (i.e., the same operating conditions), where 0 and 1 indicate liquid and gaseous nitrogen, respectively. Then, \(f{t}_{{{{{{\rm{g}}}}}}}\) is simply calculated by averaging the site-wise \(f{t}_{{{{{{\rm{g}}}}}}}\) over all nucleation sites.

Summary of the experimental results

Figure  7 shows the boiling curves of the pool (a) and flow boiling (b) experiments. Time averaged heat flux and temperature are calculated by averaging in space and time the time-dependent distributions of temperature and heat flux measured with the infrared thermometry technique discussed before. In the case of liquid nitrogen, the heat flux is assumed equal to the heating power, and the boiling surface temperature is measured using a thin film RTD, as discussed in the previous section. Figure  7c shows the distribution of the measured bubble footprint area right before the boiling crisis, i.e., at the last operating heat flux for which we could achieve a stable nucleate boiling regime. Note that, no matter the boiling curve, these distributions are all power laws. Finally, Tables  1 and 2 report the values the values of heat flux, wall superheat, average bubble radius, \(R\) , product of bubble growth time and departure frequency, \(f{t}_{{{{{{\rm{g}}}}}}}\) , and nucleation site density for all surfaces and operating conditions. We note that the value of the \(f{t}_{{{{{{\rm{g}}}}}}}\) product tends to increase for all surfaces and flow conditions with the heat flux. This observation is consistent with the observations of other scientists 25 , 26 (e.g., using sapphire-ITO heaters similar to the ones we used). Similarly, the value of the CHF measured in pool boiling on sapphire-ITO heaters is in the range of the values observed in literature 25 , 26 , 27 , 28 , 29 .

a Pool boiling curves. All experiments are run with DI water, except one, run with liquid nitrogen (LN2) (Source data are provided as a Source Data file). b Flow boiling curves. All experiments are run with DI water (Source data are provided as a Source Data file). c Distribution of the measured bubble footprint area right before the boiling crisis, i.e., at the last operating heat flux for which we could achieve a stable nucleate boiling regime. d Representation of the experimental boiling triplets ( \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}},\,R,{f}{t}_{{{{{{\rm{g}}}}}}}\) ) for several boiling surfaces and operating conditions in a 2D plot with the product \(f{t}_{{{{{{\rm{g}}}}}}}\) on the y -axis and the product \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}{R}^{2}\) on the x axis (Source data are provided as a Source Data file). The dot grayscale is proportional to the ratio between the heat flux and the maximum heat flux that each surface (represented by different line colors) can remove in nucleate boiling. White dots indicate the experimental boiling crisis and lie on the theoretical critical surface \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}{{R}}^{2}f{t}_{{{{{{\rm{g}}}}}}}=1.03\) . e Simplified view of the critical surface (dashed line) and the experimental boiling triplets ( \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}},R,f{t}_{{{{{{\rm{g}}}}}}}\) ) at the boiling crisis for all surfaces and operating conditions. Dashed lines represent the standard deviation on the theoretical critical constant.

The uncertainty on the heat flux is typically ±20 kW/m 2 and it is driven by the uncertainty on the voltage drop measurement. The uncertainty on the wall superheat, i.e., the wall temperature is within ±0.3 °C, and it is driven by the accuracy and precision of the thermocouples used for the calibration of the infrared signal. The uncertainty on the average bubble radius is within ±5 %, and it is dominated by the uncertainty on the image segmentation process. The uncertainty on the \(f{t}_{{{{{{\rm{g}}}}}}}\) product is dominated by the standard deviation of its distribution, and it is typically within ±10 %. The uncertainty on the nucleation side density is estimated within ±5%, based on a benchmark exercise comparing the measurements provided by three independent users. The effect of measurement uncertainties is shown in Fig.  7d, e . In this Figures, we plotted a 2D version of the 3D plots shown in Fig.  3 b, c. On the y -axis we have the product \(f{t}_{{{{{{\rm{g}}}}}}}\) , while on the x axis we have the product \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}{R}^{2}\) (i.e., both axes are non-dimensional). Figure  7d reports all the boiling points (i.e., it is the equivalent of Fig.  3b ), with error bars. Figure  7e only reports the points at the boiling crisis (i.e., it is equivalent to Fig.  3c ). As shown, the uncertainty in the measurements does not change the conclusions drawn based on Fig.  3 b, c.

Stochastic model

We modeled the bubble interaction process using the stochastic model introduced in our previous work 14 , 15 . This model uses measured \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , \(f{t}_{{{{{{\rm{g}}}}}}}\) , and \(\,R\) , as inputs and captures how the distribution of the bubble footprint area change with these parameters, i.e., with the operating conditions, from the onset of nucleate boiling till the boiling crisis. Given a surface of area \({A}_{{{{{{\rm{h}}}}}}}\) , we randomly create \({{A}_{{{{{{\rm{h}}}}}}}N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) nucleation sites. Selected a nucleation site, the probability that a bubble is growing out of that site, as we observe it, is \(f{t}_{{{{{{\rm{g}}}}}}}\) . Thus, given a random number between 0 and 1, if it is smaller than \(f{t}_{{{{{{\rm{g}}}}}}}\) we generate a bubble, otherwise, we move to another nucleation site. The radius of the bubble footprint, if any, is also generated randomly. It is sampled from the measured radius distribution, \({{{{{\rm{p}}}}}}\left(r\right)\) , of the bubbles that never interact with other bubbles throughout their life cycle (defined by the average footprint radius, \(R\) , through Eq. ( 9 )). We repeat this process by looping over all nucleation sites in random order. If a site is already covered by a bubble footprint (i.e., the bubble generated by another nucleation site) we move to the next site. The typical result of one iteration is sketched in Fig.  8a . At the end of every iteration, we sample the size of the bubble patches, also called bubble clusters, and then we repeat the process from the beginning, i.e., re-starting with the creation of nucleation sites, as many times as necessary to achieve a converged distribution of the bubble clusters area. Sample predictions of this model are shown in Figs.  2 e and 2f . As shown in these figures, the boiling crisis coincides with the occurrence of a power law distribution, and can be predicted based on the bifurcation of the bivariate probability \({{{{{\rm{p}}}}}}({A}_{{{{{{\rm{G}}}}}}},{A}_{{{{{{\rm{SG}}}}}}})\) of the giant and second giant bubble cluster areas (see Fig.  2f ), \({A}_{{{{{{\rm{G}}}}}}}\) and \({A}_{{{{{{\rm{SG}}}}}}}\) , respectively. Precisely, at each iteration, we sample \({A}_{{{{{{\rm{G}}}}}}}\) and \({A}_{{{{{{\rm{SG}}}}}}}\) . Doing so, after many iterations we achieve a converged \({{{{{\rm{p}}}}}}({A}_{{{{{{\rm{G}}}}}}},{A}_{{{{{{\rm{SG}}}}}}})\) distribution. Examples of \({{{{{\rm{p}}}}}}({A}_{{{{{{\rm{G}}}}}}},{A}_{{{{{{\rm{SG}}}}}}})\) in different operating conditions are provided in Fig.  8b . As shown in the Figure, the peak of the distribution experience a sudden jump in correspondence of the critical conditions, for which we observe a power law distribution. Before critical conditions the peak values of \({A}_{{{{{{\rm{G}}}}}}}\) and \({A}_{{{{{{\rm{SG}}}}}}}\) are very similar, i.e., the bubble interaction is stable. Instead, at critical conditions, there is a bifurcation with the giant cluster area growing bigger and bigger, while the second giant bubble cluster disappears (see Fig.  2f ). This instability in the bubble interaction process is the signature of the boiling crisis. We have used this model to determine critical combinations of \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) , \(R\) , and \(f{t}_{{{{{{\rm{g}}}}}}}\) , and found Eq. ( 1 ), i.e.,

as discussed in the main body of the paper. We observed that the values of \(C\) depends on the non-dimensional boiling area \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}{R}^{2}\) . We run multiple simulations of over 30,000 iterations each for several values of the non-dimensional boiling area in order to obtain statistically converged results and determine the correlation between \(C\) and \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}{R}^{2}\) . Figure  8c shows \(C\) as a function of \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}{R}^{2}\) . As the non-dimensional area becomes infinitely large ( \(\sim {10}^{6}\) ), the critical constant reaches an asymptotic value around 1.15. Interestingly, this value agrees rather well with the critical filling factor for an infinitely large system in the 2D continuum percolation with constant-size circles, i.e., 1.13 30 . This finding corroborates the idea that the boiling crisis falls into the class of first-order phase transition phenomena. Importantly, this sensitivity study reveals that, in the range of \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}{R}^{2}\) typical of our experiments, i.e., 50 to 300, but also of other experiments and applications, the mean value of the parameter \(C\) is very close to 1. Precisely, for a nondimensional area of 100, \(C\) is equal to 1.03 and has a \(\sigma\) of 0.06.

a Example of the stochastic model output for one iteration. One can recognize the presence of a giant G bubble cluster, a second giant SG bubble cluster, smaller bubble clusters and discrete, non-interacting bubbles. b Examples of bivariate distributions of the giant and second giant bubble cluster areas (in 1/mm 4 ) for subcritical (top), critical (middle), and supercritical (bottom) conditions. c Sensitivity of the critical triplet to the nondimensional area. Critical triplet (dashed) line, ± \(\sigma\) (light blue), and ± \(2\sigma\) (teal) vs. nondimensional area \({A}_{{{{{{\rm{h}}}}}}}/{{{{{\rm{\pi }}}}}}{R}^{2}\) . d Control volume for the hydrodynamic scaling analysis. The volume exchanges energy at the bottom surface (with a heat flux \({q}_{{{{{{\rm{w}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) ) and at the top boundary, by releasing bubbles and receiving saturated liquid.

In addition to this sensitivity study to the nondimensional area, we also tested the robustness of this analysis with respect to our modeling assumptions. For instance, when we sample the bubble radius according to a normal distribution with the same average value and standard deviation as the exponentially decaying function, the critical constant for the same non-dimensional area does not change. Similarly, if instead of taking a unique, fixed value for \(f{t}_{{{{{{\rm{g}}}}}}}\) , we use a distribution, e.g., power law distribution such that \(p(f{t}_{{{{{{\rm{g}}}}}}})\propto {(f{t}_{{{{{{\rm{g}}}}}}})}^{-{{{{{\rm{\gamma }}}}}}}\) , the critical constant is almost the same. Precisely we obtain 1.07 and 1.10 for \({{{{{\rm{\gamma }}}}}}\) equal to 1.5 and 2.5, respectively. However, the value of the critical constant remains within the range of its standard deviation.

Reconciling percolation and hydrodynamic theory

Consider a pool of liquid in saturated conditions and a control volume as shown in Fig.  8d . The volume exchanges energy at the bottom surface (with a heat flux \({q}_{{{{{{\rm{w}}}}}}}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) ) and at the top boundary, by releasing bubbles and receiving saturated liquid.

In equilibrium conditions, the energy balance in the control volume leads to the following scaling law:

where \({R}_{{{{{{\rm{d}}}}}}}\) is the departure radius of bubbles, \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}\) is the nucleation site density, \(f\) is the bubble departure frequency, \({\rho }_{{{{{{\rm{v}}}}}}}\) is the vapor density, and \({h}_{{{{{{\rm{lv}}}}}}}\) is the latent heat of vaporization. We may multiply and divide the right-hand side by \({t}_{{{{{{\rm{g}}}}}}}\) and rearrange this equation as follows:

We may assume that, at the boiling crisis, \({R}_{{{{{{\rm{d}}}}}}}/{t}_{{{{{{\rm{g}}}}}}}\) scales as the critical vapor velocity identified by Zuber 31 :

By substituting Eq. ( 12 ) into Eq. ( 11 ), and assuming that, everything else being the same, the bubble footprint radius scales with the bubble departure radius, i.e., \(R\propto {R}_{{{{{{\rm{d}}}}}}}\) , Eq. ( 11 ) becomes

Per our percolation criterion, at the boiling crisis we should have \({N}^{{{{\rm{{{\hbox{'}}}}}{{\hbox{'}}}}}}{{{{{\rm{\pi }}}}}}\,{R}^{2}f{t}_{{{{{{\rm{g}}}}}}} \sim 1\) . With this assumption and after some mathematical manipulations, Eq.  13 becomes

Which is Zuber’s correlation for nucleate boiling CHF 4 , 31 . At ambient pressure, the liquid density is much higher than the vapor density, thus

which is known as Kutateladze-Zuber correlation. In summary, our percolation theory provides a scaling with the fluid properties and operating conditions consistent with the scaling identified by Kutateladze and Zuber.

Data availability

Source data are provided in this paper. Other raw data are available from the corresponding author upon request.  Source data are provided with this paper.

Code availability

The computer script of the stochastic model that supports the findings of this study is available from the corresponding author upon request.

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Acknowledgements

We thank E. Baglietto, J. Buongiorno, and S. Yip for discussions. This material is based upon work supported by the U.S. Department of Energy contract No. DEAC05-00OR22725 (M.B.) and the National Science Foundation under award numbers 2019245 (M.B.) and 2018995 (M.M.R.).

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Limiao Zhang, Chi Wang, Guanyu Su, Artyom Kossolapov, Gustavo Matana Aguiar, Jee Hyun Seong, Florian Chavagnat, Bren Phillips, Md Mahamudur Rahman & Matteo Bucci

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Limiao Zhang

Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL, 61801, USA

Department of Nuclear Engineering, University of California, Berkeley, CA, 94709, USA

Los Alamos National Laboratory, Los Alamos, NM, 87545, USA

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M.B. and M.M.R. planned and supervised the project. C.W., A.K., F.C., G.M.A. and B.P. developed the experimental setups and implemented the measurement techniques. C.W. M.M.R., J.H.S., G.S., F.C. conducted the experiments. L.Z., G.S., J.H.S. and C.W. developed the post-processing techniques and analyzed the experimental data. All authors contributed to the preparation of the manuscript.

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Correspondence to Matteo Bucci .

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Zhang, L., Wang, C., Su, G. et al. A unifying criterion of the boiling crisis. Nat Commun 14 , 2321 (2023). https://doi.org/10.1038/s41467-023-37899-7

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Received : 12 November 2022

Accepted : 03 April 2023

Published : 22 April 2023

DOI : https://doi.org/10.1038/s41467-023-37899-7

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