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Cooled Off: Does Evaporating Alcohol Cool Faster than Water?

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Purpose or Problem

The purpose is to determine if the temperature of an object can be cooled more by evaporating alcohol surrounding it than by water or air.

Overview

The process of evaporation produces a cooling effect. Pour a few drops of water onto the back of your hand. Next, swing your arm back and forth. Do you feel your skin getting cooler?

Now pour a few drops of alcohol onto the back of your hand and swing your arm again. Does your skin feel even cooler?

Alcohol evaporates faster than water and, thus, creates a cooler temperature. When children run dangerously high fevers, doctors sometimes give them a bath in alcohol to reduce their external temperature, which, in turn, reduces their internal temperature.

How much change in temperature occurs between alcohol and water evaporation?

Hypothesis

Hypothesize that a greater percent change in temperature will take place when alcohol is evaporated rapidly than when water is evaporated.

Materials' List

  • Two-foot-square piece of plywood
  • Several pieces of 1×2 lumber
  • Wood screws
  • Saw
  • Screwdriver
  • Three thermometers
  • Duct tape or adhesive tape
  • Six thumbtacks
  • Old T-shirt or flannel shirt
  • Alcohol
  • Water
  • Electric fan

Procedure

Mount three thermometers side-by-side onto a piece of two-foot-square plywood, using adhesive tape or duct tape. Do not cover either the thermometer's bulb or the area on the scale around the 70°F mark. The board needs to stand vertically, so using a few pieces of small 1×1 or 1×2 lumber and wood screws, construct support struts onto the plywood to enable it to stand upright.

Cut three identical four-inch squares in a piece of an old T-shirt or flannel shirt. Fold each in half, and then fold in half again. Slip a piece of cloth over the bulb of each thermometer. Use thumbtacks to hold the cloths in place, pushing one thumbtack on either side of each bulb through the cloth and into the board.

Set the thermometers on a table. Place an electric fan in front of the thermometers, positioning the fan so a high volume of moving air hits the bulbs.

Let the thermometers sit for ten minutes to stabilize at room temperature. Label each thermometer A, B, and C. Write down the temperature reading on each thermometer. It does not matter if they are not precisely calibrated, and they do not all need to have exactly the same temperature.

Soak the cloth around thermometer A's bulb with rubbing alcohol. Soak the cloth around thermometer B's bulb with water. Leave C dry.

Turn on the fan. Monitor the three temperatures for several minutes. Record the lowest temperature reading on each thermometer.

Calculate the percent change in temperature of each thermometer. Percent change is calculated by subtracting the lowest temperature reading from the room-temperature reading, dividing that answer by the original room temperature reading, and then multiplying by 100 (to put the answer in percent). For example, if a thermometer reads 72°F at room temperature, and then drops to 68°F during the experiment:

72°F-68°F = 4°F

(4/72) × 100 = 5.56%

Did the alcohol-soaked bulb drop the lowest? Why doesn't it matter whether all the thermometers were calibrated to read exactly the same at room temperature?

Results

Write down the results of your experiment. Document all observations and data collected.

Conclusion

Come to a conclusion as to whether or not your hypothesis was correct.

Something More
  1. Does the velocity of the moving air affect the temperature of evaporation? Repeat the experiment, once with the fan on its lowest setting, and then once on its highest setting. Graph your results, drawing them on graph paper or using a computer spreadsheet program that prints graphs from entered data.
  2. In an environment where humidity is high, will the evaporation of alcohol and water still result in a cooling effect? Repeat the experiment in a steamy environment.
  3. How does the fact that evaporation causes a cooling effect relate to wind-chill factor?
  4. How do air conditioners work?
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