Drink a Cup of Saltwater?
Solar-Powered Water Desalination
Clear plastic rectangular containers with pre-drilled holes
Plastic cups with pre-drilled holes
25 mL graduated cylinder
800 mL beaker
5 mL funnels
Black construction paper
White construction paper
Plastic cling wrap
1. Fit the stem of a funnel inside the short end of a straw. Push the funnel in as far as it will go. Securely tape the straw to the funnel. Repeat for the second straw and funnel.
2. Push a straw-funnel assembly through the hole near the bottom of each container so that the funnels are on the inside of the containers. Adjust the straw-funnel assemblies so that the funnels face up. Put some modeling clay around the hole, on the outside of the container, to hold the funnel in place. Do not worry if the funnel will not stay in place. The next steps will solve that. (See picture 1)
3. Start by putting the long end of each straw through the hole in a plastic collection cup. Adjust the straw so that the funnel faces up. Put some modeling clay around each hole, on the outside of each collection cup, to keep each cup in place. (See picture 2)
4. Now you will need to do some tinkering to get everything positioned correctly: The straw should slope down slightly from the box to the cup. This will allow gravity to help the water you collect flow from the straw to the cup. If there is no slope, the water will collect in the straw rather than in the cup. If the straw is too long for the funnel to face up and the straw to slope down towards the collection cup, cut a little bit off of the long end of the straw and test the setup again. Keep cutting a little bit of the straw off and re-assembling until it is right. Do not worry if the collection cups do not sit completely flat.
5. Cover the opening of one container with a single large piece of plastic cling wrap. To seal the container closed, pull the wrap tightly over the opening and tape it in place at the four corners of the container. Repeat for the second container.
6. Set a washer on the plastic cling wrap, right above the funnel. Do this for each desalination device. Adjust as needed so that the washer creates a low point in the cling wrap right above the funnel, but make sure it is not so low that the cling wrap touches the funnel. If the plastic cling wrap is touching the funnel, not all of the condensation will go down into the funnel. To fix this, either lower the funnel (such as by cutting the straw) or raise the cling wrap (by taping it tighter). If the cling wrap is so tight that it does not form a low point where the washer is, un-tape it in places and re-tape it more loosely.
5. After you are done adjusting your setup, cover each collection cup with plastic cling wrap and secure the plastic tightly with a rubber band. This prevents your desalinated water from evaporating.Make sure that there are no gaps or holes in the cling wrap.Secure a piece of cling wrap on to the top of each collection cup using a rubber band.
6. Cover the outside bottom of one desalination container with black construction paper and cover the other one with white construction paper. Tape the paper in place. Arrange the construction paper so that it goes up about 2 to 3 cm on the sides of each container. You may need to cut a small slit in the construction paper for the straw to get through.
7. Make up a single batch of saltwater for both desalination containers. Add 1 tablespoon of salt to the tripour beaker and fill it with tap water to the 500 mL mark. Mix with a spoon until the salt is dissolved. Each of the desalination containers will need 250 mL of saltwater.
8. For each desalination container, remove the washer, gently remove the tape on one corner, lift the cling wrap, and pour in the saltwater. Add enough so that it just barely covers the bottom of the container, approximately 250 mL per container. Be careful not to let any saltwater spill into the funnel or onto the construction paper.
9. Put the cling wrap back in place, making sure it is taped on all four corners of each container. Put the washer back on top of the plastic wrap directly above the funnel. Your desalination devices are now ready for testing!
Testing the Desalination Devices
In this part of the science project, you will test the performance of the desalination devices.
1. Carefully take the desalination devices outside to an area that will receive direct sunlight for at least four hours. Prepare your desalination devices for testing and do a final check to make sure that everything is in place and ready.
2. In your lab notebook, record the time. Measure and record the temperature near the desalination devices. You can use this information later to determine how temperature affects the condensation yield.
3. Check on the desalination devices after about 30 minutes. You may see condensation starting to form small drops on the cling wrap right below the washer. However, it may take longer, depending on how sunny and warm it is.
4. Continue checking on your desalination devices every 30 minutes to make sure that they are still in the sunlight and that the condensation drops are falling into the funnel.
5. Leave your desalination devices in the sunlight for at least four hours before stopping your experiment. In your lab notebook, record the time when you stop your testing. How long were your desalination devices in the sunlight?
6. Open the large cling wrap covering on each device and try to get any condensate that is still in the straw to go out and into the collection cup. You can do this by gently blowing into the straw. To determine the condensate yield of each desalination device, carefully disconnect the collection cup, remove its cling wrap covering, and pour the collected condensate into the 25 mL graduated cylinder. What was the condensate yield of each device? Record your results in your lab notebook.
7. To determine whether the collected condensate is still salty, taste a little bit from each device. Record your observations in your lab notebook.
8. Repeat this experiment at least two more times on different days for a total of three trials. This will help ensure that your results are consistent and reproducible. Between trials, carefully rinse out each desalination device with tap water and let them dry along with all of the other desalination device components. Use the same amount of saltwater in each device and trial.
Key words: Solar-Powered Water Desalination
The stronger the wind the higher the rate of evaporation.
The higher the temperature the higher the rate of evaporation.
More humidity means less evaporation
Solar power turns the suns energy into electricity
Water desalination takes unwanted minerals from saltwater that we can use for drinking or agriculture.
In distillation salt water gets heated up in one container to make the water evaporate that leaves the salt that was in the water behind. Then the water vapor without the salt condenses into a separate container. This method has been used for many years but is rarely used because of the costs of fuel need to turn the saltwater to freshwater. But there have been technological advances led to more efficient desalination units using solar energy, however these units have very small capacities so their use is limited.