Introduction: (Initial Observation)
Washed fabric, painted walls, wet towels and many industrial products need to dry by the process of evaporation. For example laundry detergents that are powder, have been liquid in some stage of their production; they have been dried in large dryers to become dry powder. If we know what affects the rate of evaporation most, we can design better dryers and reduce the cost of any process that involves some evaporation.
Find out about evaporation and its importance in drying wet fabric or wet lands. Read books, magazines or ask professionals who might know in order to learn about the factors that affect the rate of evaporation. Keep track of where you got your information from.
Following are samples of information that you may find.
Gathered information indicates that the rate of evaporation is not the same in all liquids. For example organic solvents such as alcohol evaporate much faster than water. We concentrate our research on water evaporation. When water evaporates, it goes back into the air in little, tiny drops that we can hardly see.
Search the Internet for the word evaporation. You will soon see that evaporation is a major concern for many people in many areas. Farmers are concerned about evaporation of water and drying soil, health specialists are concerned about evaporation of water from human body, Industrialists are concerned about unwanted evaporation of liquids that is a daily loss for them. Some others are concerned about the cost of evaporation in drying products.
What is Evaporation?
Evaporation is the change of water from a liquid state into a vapor. It is commonly used to describe the loss of water from an open water surface. Transpiration is the movement of water from the soil through a plant and then out the pores on the leaves and into the atmosphere. There is also the evaporation of water from the soil and wet vegetation. All of these sources of water vapor in the atmosphere can be grouped together in the term evapotranspiration. Different authors can mean slightly different things with evapotranspiration, so one needs to examine the context in which the term is being used.
Can you write a list of benefits of evaporation?
1. Water regenerates and is redistributed through evaporation.
2. Sweat cooling off your body by evaporation.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to see how (at what rate) different factors affect the rate of evaporation. Specific questions for this study are:
How does the temperature affect the rate of evaporation?
How does wind affect the rate of evaporation?
How does moisture affect the rate of evaporation?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Independent variable is the specific factor (Heat, wind, surface area, ..) that may affect the rate of evaporation.
Dependent variable is the time it takes for certain amount of water to evaporate.
Constants are the type of water, amount of water, cost of energy and equipment used in each evaporation method.
Controlled variables are all other environmental factors that may affect evaporation. For example while testing wind method, we make sure that no temperature increase has happened at the same time.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis:
Wind and heat (like a hair dryer) must be the most effective factors on evaporation. Moisture will have a negative affect, because in the days that we have a lot of moisture in the air, washed clothes do not easily dry when we hang them outside.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
In order to find out which evaporation method is more effective, we try different evaporation methods and see how long does it take for a certain amount of water to evaporate with each method.
Each of the following experiments test one of the methods.
The effect of heat on evaporation
Note about variables: Since we want to test the effect of heat, we must make sure that all other variables such as wind and moisture will have no affect on the results.
Get 5 jars or cups, fill them up with water, Mark the water level and place them in different locations inside your house where temperatures are different. For example next to a hot water pipe, radiator or behind a refrigerator you can find hot places.
As you get away from your heat source, you will get less heat and finally you may place one cup inside a refrigerator. It is good if you cover the jars with a thin fabric in a way that evaporated water can exit, but wind can not enter. Also it is good if all 5 samples will be in the same elevation from the ground. Depending on the weather, you may have higher or lower moisture in different elevations.
Inspect the water level, mark it on the jar and record it on a table similar to the following:
Evaporation in millimeter:
|Jar 1 (110ºF)||Jar 2 (90ºF)||Jar 3 (70ºF)||Jar 4 (50ºF)||Jar 5 (30ºF)|
Use a room thermometer, inspect the temperature next to each jar and write the actual temperature, it does not have to be the same temperatures that we have in the above table. For more accuracy of your measurement, you may photocopy a ruler and attach it to the side of the jars.
The effect of wind on evaporation
Note about variables: Since we want to test the effect of wind, we must make sure that all other variables such as heat and moisture will have no affect on the results.
Get 5 jars, fill them up with water, mark the water level and place them in front of an electric fan. Place them in a way that Jar number 1 will get the most wind, Jars number 2, 3 and 4 will each get less wind than previous and finally jar number 5 will get no wind.
Inspect your setup every 12 hours and record the water level in a table similar to the following:
Evaporation in millimeter:
| Jar 1
| Jar 2
2nd most wind
| Jar 3
3rd most wind
| Jar 4
| Jar 5
The effect of moisture on evaporation
Since we want to test the effect of moisture, we must make sure that all other variables such as heat and wind will have no affect on the results.
Prepare five jars like previous experiments, cover the jars to trap the moisture in different rates. For example the first jar will remain open, second jar will be partially (25%) covered with a piece of plastic. 3rd jar will be 50% covered and 4th jar will be 75% covered. And finally cover the last jar with a lid or with a plastic to completely trap the moisture.
For faster results place the jars in a warm place, next to each other, so they will all be in the same heat and light and etc.
Inspect the jars and record the water level every 12 hours in a table similar to two previous table.
The effect of other factors on evaporation:
Now that you are an expert in testing evaporation, test the effect of light, surface area, vibration or stirring and spraying or any thing else that you think it might affect drying.
Materials and Equipment:
- Room thermometer
- Cups or jars
- Pieces of a thin clothe
- Electric fan
No calculations is required for this project.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Visit your local library and find books related to evaporation. Evaporation is also discussed in some physics, chemistry and meteorological books.
Following are some web resources.