The Effect of Wind Speed, Air Humidity, and Air Temperature on Evaporation Rate

Photo of Kaiti at Mid Columbia Science Fair

Researched by Kaiti D.
2005-06





 PURPOSE

The purpose of this experiment was to compare the effect of wind speed, air humidity, and water temperature on the evaporation rate of water.

I became interested in this idea because I knew that water evaporation could be helpful when it cooled you down and harmful when it dehydrated both plants and people, so I decided to learn more about what affected evaporation.

The information gained from this experiment could help food producers who dehydrate fruit, vegetables, or meat.  It could also help coaches and athletes who need to keep cool during strenuous exercise, and people who are interested in outdoor activities, such as camping, hiking, or swimming.


HYPOTHESIS

My hypothesis was that the temperature of the air would affect evaporation rate most.

I based my hypothesis on a diagram I found in Young Scientist Encyclopedia.  The diagram showed that the warmer the water, the more molecules escaped as vapor.

I also based my hypothesis on a slideshow I saw on the movie “Bill Nye the Science Guy: The Water Cycle.”   It showed that boiling water’s molecules have more energy and escape as vapor at a much faster pace than molecules at room temperature.


EXPERIMENT DESIGN

The constants in this study were:
•    The type of water (tap)
•    The amount of water
•    The location the water is placed
•    The size of the container
•    The ruler
•    The number of trials conducted
•    The type of the container
•    How long the water has to evaporate

The manipulated variables were air humidity, wind speed, and water temperature.

The responding variable was the amount of water evaporated in 150 minutes.  I measured the water in a graduated cylinder before and after the evaporation occurred.

To measure the responding variable, I measured the water in milliliters before and after the evaporation occurred.


MATERIALS


QUANTITY
ITEM DESCRIPTION
1
Small room fan
3
Liters tap water
5
Small dishes
1
Small air humidifier
1
100 ml. graduated cylinder
1
humidity meter
1
room thermometer
1
lab thermometer
1
plastic jug (approx. 4 liters)

 

 
PROCEDURES

1.    Collect materials.
2.    Stabilize and maintain the humidity in testing room using a small air humidifier as needed.  For the first phase of testing, the humidity should be about 34%.
3.    Stabilize and maintain the temperature in testing room.  For the first trials the room temperature should be 10º C.
4.    Stabilize and maintain the air speed in testing room using a small fan as needed.  For the first trials the wind speed should be “dead calm”.
5.    Place a jug of tap water in the testing room so it adjusts to the room temperature.  Whenever the water temperature is the same as the air temperature, the experiment can continue.
6.    Pour 100 ml. of tap water from the jug at the current temperature into each of 5 identical small dishes using a graduated cylinder.
7.    Place the dishes so they are being equally affected by room temperature, humidity, and air movement.
8.    Using a timer, let the water sit in the testing room for 180 minutes.
9.    Using a graduated cylinder, measure the water remaining from each dish and subtract each from the original 100 ml.
10.    Record this as how many milliliters evaporated for that trial.
11.    Repeat steps 4-10, except turn the fan on to its high-speed setting.  Be careful when placing the dishes that all are equally affected by the moving air.
12.    Repeat steps 3-11, but stabilize and maintain the temperature at 20º C.
13.    Repeat steps 3-11, but stabilize and maintain the temperature at 30º C.
14.    Repeat steps 2-13, but stabilize and maintain the humidity at about 65%      for the entire series of trials.


RESULTS

The original purpose of this experiment was to compare the effect of wind speed, air humidity, and water temperature on evaporation rate of water.

The results of the experiment were that wind speed affected evaporation rate most.  The difference between the two wind speeds evaporated water is 4.4 ml.

See the table and graph below.

 
CONCLUSION

My hypothesis was that the temperature of the air would affect evaporation rate most.

The results indicate that this hypothesis should be rejected, because wind speed affected evaporation rate most.  The temperature of the air did not matter nearly as much as the wind speed and air humidity in the room when you are testing evaporation rate.

After thinking about the results of this experiment, I wonder if the size of the room would affect how much water was evaporated.  Water in dishes set in a closet might evaporate very differently than in a gymnasium.  All liquids can evaporate but they do so at varying rates. It would be interesting to see what happens to a fast evaporating liquid like rubbing alcohol using my same procedures.

If I were to conduct this project again, I would do many more trials of each variation.  I would still use five dishes at a time, but I would do at least three different batches of five for each temperature, wind speed, and humidity condition.  I am sure that each evaporation trial should have been much longer, probably five to eight hours long.  That would have given a better idea of what happened with each condition.  It would also have been better to add an intermediate wind speed, about halfway between high and zero.

RESEARCH REPORT

I.        Introduction

Evaporation effects how people live every day.  It affects profits for people like food dehydrators, who need evaporation to dehydrate the food.  It also affects the health of humans and animals that need a sufficient water supply to live.

II.        States of Matter

The three main states of matter are liquids, (such as water), gases, (such as oxygen), and solids (such as wood.)  All three of these states are made up of microscopic particles, but the behaviors from particles differ in the three phases.
 
The particles in solid objects are tightly packed, and they are normally in a regular pattern.  Although the particles will vibrate, they generally do not move from place to place.  Solids can change their shape only if great force is applied.  For example, sawing wood, chiseling rock, cutting diamonds, or burning coal can alter the shape of a solid.

Liquid molecules are close together without any regular arrangement.  Even though the particles can move about, they can only just slide past each other.  When liquid is put into a container the particles assume the shape of the container.  Liquids can flow, spill, or pour, but they cannot be held without a container.

Gas also assumes the shape of the container it is put into.  Molecules in gas are well separated, and like liquid particles, they have no regular arrangement.  Gases also vibrate, but they move freely at high speeds.  Unlike solids and liquids, gas is usually invisible.

Elements and compounds can move from phase to phase when a special physical force is present, such as heat energy.  A phase in the states of matter changes when the temperature does; as the temperature rises, matter will move to a more active state.

III.    Evaporation

Evaporation is the process in which a liquid turns to a gas by increased molecular energy.

Energy in the form of heat causes evaporation.  Any amount of heat will cause water to evaporate, although water evaporates faster at a higher temperature.

Molecules of all substances have a certain amount of kinetic energy, which provides heat to or receives heat from its surroundings, including nearby molecules.  The more energy the molecules gather, the faster the molecules move, which makes it possible to break the bonds that hold them together.  The molecules then have enough energy to escape from the substance’s surface as vapor, hence, causing evaporation.

The wind transports water all around the earth when it is in vapor form.  This action influences the humidity of the air throughout the world.

Approximately 80% of all evaporation is from the oceans.  The remaining 20% is from inland water and different vegetation. 

The opposite of evaporation is condensation.  It occurs when vapor molecules lose energy and reform as a liquid.

Evaporation is a phase in the hydrological cycle, or the water cycle.  There are four main phases in the hydrological cycle: evaporation, condensation, precipitation, and collection.  Evaporation, the first phase, is when a liquid substance turns to vapor when heated.  Condensation happens when the vapor reaches the clouds, cools off, and changes back to a liquid.  Precipitation occurs when the water falls back to earth as rain, sleet, snow, hail, or frost.  Collection, the last phase in the hydrological cycle, is when the water runs downhill and collects in lakes, rivers, streams, seas, or oceans.

Many things influence evaporation rate.  If the air already has a high concentration of the substance evaporating, then the given substance will evaporate slower.  If the air is already saturated with other substances, almost none will evaporate. Another thing that influences evaporation rate is the temperature of the substance, because the hotter the substance, the faster the substance evaporates.  The flow rate of air affects evaporation rate because if fresh air is moving over the substance all the time, then the concentration in the air just above is less likely to go up with time, encouraging faster evaporation.  Inter molecular forces also affect evaporation rate.  The stronger the forces that are keeping the molecules together in a liquid or solid state, the more energy that must be input to evaporate them.

II.    The Laws of Thermodynamics

The first law of Thermodynamics states, in short, you cannot create or destroy energy.  Energy can change from one form to another, like electricity converting into heat, or heat converting into light.
   
The second law of Thermodynamics is that energy can flow only one direction.
“Energy spontaneously tends to flow only from being concentrated in one place to becoming diffused or dispersed and spread out.”
In other words, heat energy moves toward neighboring regions having less heat.

IV.    Summary

So, in conclusion, evaporation affects many humans’ and animals’ life, health, and profits.  Evaporation dehydrates food for profits and keeps people with a renewable supply of water.  Heat, wind speed, and humidity (saturation) all affect evaporation rate.

BIBLIOGRAPHY
 
“Evaporation and Condensation.” Young Scientist Encyclopedia.    
                                    
“Evaporation System Information.” http://www.rgf.com/products/evaporationinfo.html

“Evaporation: the Conversion of Water.”  October 26, 2005. http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/hyd/evap.rxml

“Evaporation.” http://en.wikipedia.org/wiki/Vaporation

Fox, Mary Anne.  “Evaporation.”  World Book Encyclopedia. 2002.

Illustrated Fact Book of Science.  New York: Arco Publishing, Inc.

Kahl, Jonathon D.  Weather Watch-Forecasting the Weather.  Lerner Publications Company

Kahl, Jonathon D.  Wet Weather.  Minneapolis: Lerner Publications Company, 1992

“States of Matter.”  http://www.ajkids.com/main/followup.asp?aj

“States of Matter.”  http://www.chem.purdue.edu/gchelp/atoms/states.html

The American Heritage Student Dictionary. Houghton Mifflin Company. Boston. 1994

“The Second Law of Thermodynamics.”  January 18, 2006. http://www.secondlaw.com/two.html

“The Water Cycle.”   Rabbit Ears Productions.  1995.

“What is Matter.”  November 2, 2005.
 http://www.nyu.edu/pages/mathmol/textbook/statesofmatter.html
 


ACKNOWLEDGEMENTS

I would like to thank the following people for helping make my project possible:
•    My parents for helping me with my project and giving me ideas.
•    Mr. Newkirk for providing me with the thermometer that made my experiment possible and correcting my written work.
•    Jordan, Tensie, Kacey, and Taylor, for helping me when I couldn’t find information.
•    Mrs. Viernes for helping me whenever I had a problem with my computer.


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