How to Determine Evaporation Rates

Written by william hirsch
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How to Determine Evaporation Rates
Use a measuring cup to find a fluid evaporation rate. (BananaStock/BananaStock/Getty Images)

Learn to determine the rate of evaporation of a liquid using basic tools and simple mathematics. The evaporation of a liquid occurs across the surface of the substance that is in contact with the air. The rate of evaporation is affected by the current air humidity, wind speed and air temperature. Any liquid will evaporate given the right conditions, but the rate varies with their chemical composition. More chemically complex liquids, such as gasoline, take longer to evaporate than water.

Skill level:

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Things you need

  • Graduated measuring cup
  • Stop watch
  • Calculator

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  1. 1

    Write down the current temperature, humidity and wind speed if performing the experiment outdoors. The information may be obtained from a local weather report. This data can be used as a log to compare evaporation rates under different conditions for the same liquid.

  2. 2

    Fill the graduated cup to the top measurement line. For example, assume the reading is 10 fluid ounces. Start the stop watch.

  3. 3

    Stop the timer when the liquid level has clearly fallen to another measurement line in the cup. For example, assume the liquid drops to six fluid ounces in three hours.

  4. 4

    Subtract the final liquid level from the initial to get the difference. Completing this step, for the example, you have 10 fluid ounces minus 6 fluid ounces, or 4 fluid ounces.

  5. 5

    Divide the fluid level difference by the time elapsed to arrive at the evaporation rate. Completing the example leads to 4 fluid ounces divided by 3 hours, or an evaporation rate of 1.3 fluid ounces per hour.

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