Which Liquid Works Best for Evaporative Cooling?

Abstract

When we get hot, we sweat. Sweating helps cool us down. When the water evaporates, it removes energy from our bodies. This sort of evaporative cooling can also be used to cool homes using what are referred to as swamp coolers. In some cases, these coolers may be more energy-efficient than traditional air conditioners. In this chemistry science fair project, you will find out which liquid works best for evaporative cooling.

Summary

Areas of Science

Chemistry
Environmental Engineering

Difficulty

Method

Scientific Method

Time Required

Average (6-10 days)

Prerequisites

None

Material Availability

Readily available

Cost

Low ($20 - $50)

Safety

No issues

Credits

David Whyte, PhD, Science Buddies

Ben Finio, PhD, Science Buddies

• Styrofoam^TM is a registered trademark of The Dow Chemical Company.

Science Buddies is committed to creating content authored by scientists and educators. Learn more about our process and how we use AI.

Image Credit: Ben Finio / Science Buddies

Objective

Determine which liquid works best to lower the temperature of a paper towel during evaporative cooling.

Introduction

Evaporation is the process by which molecules in a liquid escape into the gas phase. In any liquid, such as a glass of water at room temperature, the molecules in the liquid are moving. They bump into each other as they meander about the liquid. The speed with which they move depends on the temperature—in hotter liquids, the molecules move faster. The average speed depends on temperature, but around this average speed, there will be some molecules moving faster (more energetically), and some moving slower. When the more-energetic molecules are near the liquid's surface, they can escape into the gas above. As more and more of the most energetic molecules evaporate into the gas, the average energy of the molecules left behind decreases, so the liquid cools.

The rate of cooling caused by evaporation depends on the rate at which molecules can escape from the liquid. You might have noticed that when you pour rubbing alcohol on your skin, it cools your skin more than when you pour water on it. This reflects the greater volatility, or tendency to evaporate, of the rubbing alcohol. The process by which evaporation cools your skin is called evaporative cooling.

In the procedure of this project, you will compare evaporative cooling caused by water, rubbing alcohol, and cooking oil. The cooling effect studied in this part of the procedure is the basis for swamp coolers (Figures 1 and 2). In these cooling devices, outside air is blown over a wet surface and then into the home. You are familiar with the principle if you have ever had wet clothes on with a breeze blowing—the evaporation of water cools you off, just as it cools the wet surface in the swamp cooler. Thermal energy in the hot air is "extracted" and used to convert some of the liquid water into water vapor. Because energy is used to evaporate water, the air is cooled after passing over the wet surface. The cool air is then circulated around the interior of the building.

Which liquid do you think will work best for evaporative cooling? Try this experiment and find out!

Image Credit: لا روسا / Creative Commons Attribution-Share Alike 4.0 International
Figure 1. An Egyptian jar used for evaporative cooling. The porous jar is filled with water and wrapped with a coarse cloth.

Image Credit: Utkarshingh.1992 / Creative Commons Attribution-Share Alike 1.0 Generic
Figure 2. An evaporative cooler in India. A fan blows air over a container of water.

Terms and Concepts

• Evaporation
• Volatility
• Evaporative cooling
• Swamp cooler
• Energy

Questions

• Why are some liquids more volatile than others?
• Swamp coolers are most often used in areas that are hot and dry. Would a swamp cooler work in hot, muggy conditions?
• Dogs do not sweat, but is their cooling mechanism similar to that of humans?
• What other factors, beyond which one cools the most, would you need to consider when selecting a liquid for evaporative cooling of a building? Are there any safety or health concerns for certain liquids? What about availability?

Materials and Equipment

• Measuring cup
• Water
• Rubbing alcohol
• Cooking oil, such as olive oil
• Plastic plates, disposable (4)
• Paper towels (12)
• Clear tape
• Ballpoint pen
• Infrared thermometer; available online, from websites like Amazon.com
• Stopwatch
• Small fan; if you do not have a small fan, you will need an extra plate.
• Lab notebook
• Graph paper

This project follows the Scientific Method. Review the steps before you begin.

1. Fill a measuring cup with tap water and allow it to come to room temperature.
   1. The rubbing alcohol and the oil should also be at room temperature.
   2. This step is just to ensure that the liquids are at the same temperature at the start of the experiment.
2. Place four disposable plastic plates, with the up sides down, on a work surface.
   1. Use a waterproof surface (such as tile or laminate) since you will be using alcohol that could damage wood finish.
3. Fold each paper towel in half twice so that each has four layers.
4. Place a folded paper towel on top of each plate.
   1. The plates keep the towels from being in contact with the work surface, which would affect their temperature. You could also use Styrofoam^TM or other insulating material.
5. Tape the edges of the paper towels to the plates.
6. Label the paper towels 1–4.
   1. In the next step, the paper towels will be treated as follows:
      • 1: no liquid
      • 2: water
      • 3: rubbing alcohol
      • 4: oil
7. Take the temperature of the paper towels with the infrared thermometer.
   1. Take three readings of each paper towel.
   2. Keep the direction and distance between the thermometer and each plate the same.
   3. Record the temperatures and times in a data table in your lab notebook. See Table 1 for an example.
8. Slowly pour liquid onto three of the paper towels. Pour just enough liquid to wet them completely, but not so much that the paper towels are completely saturated and liquid starts pooling on top or dripping from the sides.
   1. Pour water onto paper towel #2.
   2. Pour rubbing alcohol onto paper towel #3.
   3. Pour oil onto paper towel #4.
9. Start the stopwatch.
10. Take the temperature of each paper towel, and record the temperature and time in your lab notebook.
11. Repeat the temperature readings three more times, at 2-minute intervals.
12. Which paper towel has the lowest temperature? What was the largest temperature difference between two paper towels that you noted? Record all observations in your lab notebook.
13. Repeat steps 1-14 two more times, with fresh paper towels, but you can rinse and reuse the plates. You will need a new data table for each trial. Average the results in your final report.
14. Repeat steps 1-15 three more times, only for these trials, with the fan gently blowing over the paper towels. Make sure you clearly label your data tables so you know which ones have data for the fan. If the plates or paper towels blow away, reduce the fan speed or move it farther away. You can also tape the plates down. If you do not have a fan, use a paper plate as a fan. Your helper can fan as you take and record the temperature at 2-minute intervals. Did the fan change the results? Why?
15. Based on your results, which liquid would you recommend for a building's evaporative cooling system? Remember that you may need to consider other factors beyond which liquid got the coldest. For example, would any of these liquids pose a safety or health hazard? Which liquid is the cheapest and most readily available?

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Swipe left to see more

	Dry			Water			Alcohol			Oil
	Measurement #			Measurement #			Measurement #			Measurement #
Time	1	2	3	1	2	3	1	2	3	1	2	3
0 minutes (before adding liquid)
0 minutes (after adding liquid)
2 minutes
4 minutes
...

Table 1. Example data table.

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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Affordable and Clean Energy: Ensure access to affordable, reliable, sustainable and modern energy.

This project explores topics key to Sustainable Cities and Communities: Make cities inclusive, safe, resilient and sustainable.

This project explores topics key to Responsible Consumption and Production: Ensure sustainable consumption and production patterns.

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