Abstract

Objective

Use an anemometer and an infrared thermometer to determine how wind speed affects the rate of cooling of an object.

Introduction

The windchill factor describes what happens to an object (like your body) when it is cold and windy outside. As wind increases, heat is carried away from the body at a faster rate, driving down both skin temperature (which can cause frostbite) and eventually the internal body temperature (which, in extreme cases, can lead to death). Windchill charts are useful to help predict when a person is most in danger of frostbite, which damages skin and other tissues due to extreme cold. The chart in Figure 1, below, shows how wind speed affects the time it takes to develop frostbite at various temperatures. On the left side of the chart, the temperatures are relatively high, meaning there is no danger of frostbite (light blue). As it gets colder, the danger of frostbite increases. If you are outside when the temperature is 0°F and the wind is blowing at 30 miles per hour (mph), you could develop frostbite within 30 minutes on exposed parts of your body (usually your fingers and face). If it is minus 25°F and the wind is blowing at 40 mph (this is in the purple part of the chart), you could get frostbite in as little as 5 minutes!

Figure 1. Windchill chart. (Wikipedia, 2009.)

There are two ways that the wind cools things off. The first way is by simply blowing away the warm air that is next to your skin and replacing it with cold air. This is called convective cooling. Another way it cools is by evaporating the moisture on your skin. As the moisture evaporates, it causes the surface to cool. This is called evaporative cooling. Both kinds of cooling occur on human (and animal) skin that is exposed to cold wind.

For an inanimate object that has a dry surface, only convective cooling occurs. In convective cooling, the object can only be cooled to the temperature of its surroundings. For example, if you put a cup of hot coffee on a table, it will eventually cool to room temperature. If you blow on it with a fan, it will cool faster, but it will only cool to room temperature and no further. What happens if you spray the cup of hot coffee with a mist of water while you are blowing on it with a fan? It is then being cooled by both convective and evaporative means; thus, it will cool faster than the dry cup and will also cool to a temperature a little below room temperature.

In this science fair project, you will measure how wind speed affects the rate of cooling of an object. The speed of the wind will be measured using a handheld device called an anemometer. The anemometer measures wind speed by measuring how fast the wind makes a fan blade turn. As the wind blows, it spins the fan blades and a tiny generator to which the fan blades are attached. The generator subsequently produces a voltage that is proportional to the speed of the wind, measured by an electronic circuit that gives an instant readout of the wind speed on a digital display. The surface temperature of the object will be measured using an infrared thermometer.

Terms, Concepts, and Questions to Start Background Research

• Windchill
• Frostbite
• Convective cooling
• Evaporative cooling
• Anemometer
• Generator
• Voltage

Questions

• In what areas of the world are you most likely to get frostbite?
• Based on your research, what are some different ways scientists have developed to measure wind speed?

Bibliography

• National Oceanic and Atmospheric Administration (NOAA). (2008, February 25). Windchill Terms and Definitions. Retrieved July 15, 2009, from http://www.nws.noaa.gov/om/windchill/windchillglossary.shtml#temp

• HowStuffWorks, Inc. (2009). How does the windchill factor work? Retrieved July 15, 2009, from http://science.howstuffworks.com/question70.htm

For help creating graphs, try this website:

• National Center for Education Statistics. (n.d.). Create a Graph. Retrieved June 2, 2009, from http://nces.ed.gov/nceskids/CreateAGraph/default.aspx

Materials and Equipment

• Handheld anemometer; available online from Amazon.com
• Infrared thermometer; available online from Amazon.com
• Large electric fan, 3-speed
• Tape measure
• Masking tape
• Washable marker
• Lab notebook
• Graph paper
• Coffee cups (identical), with handles (2)
• Liquid measuring cup
• Saucers that match the coffee cups (4)
• Microwave or stovetop to heat water
• Stool, or other object about 1 meter (m) high to hold the coffee cup
• Helper

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Experimental Procedure

Note: Prior to testing, you should read the instructions for the anemometer and the infrared thermometer. Practice using both of them.

Setting Up the Test Area

1. Place the fan in a room with at least 3 meters (m) of open space in front of the fan.
2. Point the fan in the horizontal direction you will use for the experiments.
3. The center of the fan should be at the height of the stool.
1. If you are not able to adjust the height to 1 m, use the available height and modify the procedure accordingly.
4. Make a 3-m line on the floor with masking tape, starting at and leading away from the fan.
5. Mark the masking tape every 0.5 m, using the washable marker.
1. For the procedure below, you will just use the mark at 1 m. Use the other markings if you choose to collect more data.

Measuring the Wind Speed

1. Turn the fan on at its lowest setting.
2. Place the stool at the 1-m distance from the fan and measure the wind speed with the anemometer.
1. Use meters per second (m/s) as the units for wind speed.
2. Measure the wind speed at the height of the top of the stool.
3. Repeat step 1 of this section for the fan's middle and top speeds.
4. Make a data table that contains the fan settings and corresponding wind speeds at 1 m from the fan.
5. Graph the data, with the fan setting on the x-axis and the wind speed on the y-axis.

Measuring How the Wind Affects the Cooling Rate of a Cup of Coffee

Note: It may take several tries to get this procedure to go smoothly. A helper can read the temperatures as you record the data.

1. Label the two cups "1" and "2" using the masking tape and marker.
2. The stool should be 1 m away from the fan.
3. Fill two identical coffee cups with equal volumes of water (200 mL, for example) and microwave them until they are boiling.
4. Take the cups out of the microwave and place them on saucers.
5. Place another saucer on top of each of the cups to prevent evaporation.
6. Start the timer.
7. Measure the temperature of the coffee cups, as follows:
1. Use the infrared thermometer to read the temperature of the side of the cup.
2. Read the temperature on the side of the cup opposite from the handle.
3. Try to be consistent in the angle and distance used to take readings with the thermometer.
4. Record the time that you took the temperatures in your lab notebook.
5. The starting temperatures of the cups should be the same.
8. Place coffee cup #2 on a saucer on a surface that is away from any drafts.
9. Place coffee cup #1 on a saucer on the stool.
10. The handle of the cup should face away from the fan.
11. Turn the fan to its lowest setting.
12. Record the temperature of each coffee cup at 1-minute intervals for 10 minutes.
1. Read the temperature on the side opposite the handle.
2. Feel free to modify the times that you take the temperatures.
13. Repeat steps 3–13 of this section two more times. This enables you to show that your results are repeatable.
14. Repeat steps 3–13 of this section with the fan set to medium and high speed.
15. Graph the data.
16. Make three graphs, one for each wind speed.
1. Calculate the average temperatures for each time point.
2. Label the graphs with the fan setting (low, medium, and high) and the wind speed (in meters per second).
3. Put the time on the x-axis and the average temperature of cups 1 and 2 on the y-axis.
4. How does wind speed affect the rate of cooling?
17. On a separate graph, graph the rate of cooling for cup #1 at low, medium, and high wind speeds.
1. Graph time on the x-axis and the average temperature on the y-axis.
2. Compare the rates of cooling.

Variations

• Measure how evaporation affects the rate of cooling. Repeat the procedure above, but add a third cup that is placed in the wind and is sprayed with water mist. Hint: Don't forget to add a control cup of hot water that is sprayed with water, but not placed in the wind.
• Pick a temperature (for example, 60°C) and note how long it took to reach this temperature for cups 1 and 2 in the different wind speeds. Graph the wind speed on the x-axis (the x-axis will have cups 1 and 2 at the lowest speed, cups 1 and 2 at the medium speed, and cups 1 and 2 at the high speed), and the time to time it took to reach this temperature on the y-axis. Discuss the results.
• Devise windchill experiments that are performed at cold temperatures. For example, place cups of room-temperature water in a refrigerator and blow wind on one of them with a battery-powered fan. Graph time on the x-axis and temperature on the y-axis.
• Build your own anemometer, as shown in the Science Buddies project How Does a Wind Meter Work? and use it to do this science fair project.

• For more science project ideas in this area of science, see Weather & Atmosphere Project Ideas.

Credits

David Whyte, PhD, Science Buddies

Last edit date: 2011-10-18 09:00:00