09-10-2010, 05:07 PM
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Abstract
Here is a cool project about making fresh water from salt water using solar power. The apparatus is made from readily available materials, and the power source is free. How much water can the device produce, and by how much is the salt concentration reduced? Can you figure out ways to make the collection efficiency even higher? This is a great project for inventive thinkers.
Introduction
Nicholas Kinsman is interested in inventing solar-powered devices to reduce our dependence on other energy sources. He's also a winner of a Science Buddies Clever Scientist award for his 2007 California State Science Fair project (Kinsman, 2007). Nicholas set out to build a simple, inexpensive device to desalinate sea water, using readily available materials and easy construction methods.
Typical sea water contains dissolved salts at concentrations between 32 and and 37.5 parts per thousand. That means that if you started with one kilogram of sea water and then you allowed all of the water to evaporate, you'd be left with between 32 and 37.5 grams of salts (also called "total dissolved solids").
With all of that salt, sea water is not suitable for drinking nor for watering most plants. The fluid circulating in your body (blood plasma), contains much less salt than sea water (on the order of 9 grams of total dissolved solids). If you were to drink sea water, your body would actually lose water, because the high salt concentration of the sea water causes an osmotic pressure gradient which drives water out of your cells. Desalination is the process of removing the dissolved salts from water, making it pure enough for drinking or irrigation.
Nicholas's first design for a desalination device is shown in Figure 1. There are eight small bottles surrounding the large collection bottle. Each of the small bottles is filled with sea water. The small bottles have holes in their caps. One end of a flexible straw is inserted into the hole, and the other connects to the large collection bottle at the center. The idea is that the sea water in the small bottles heat up in the sun, the water vapor then condenses in the straws and flows down into the collection bottle. Unfortunately, the idea did not work. You can see in the picture that there is condensation on the inside of the top of the bottle, but there was very little condensation in the straws.
Abstract
Here is a cool project about making fresh water from salt water using solar power. The apparatus is made from readily available materials, and the power source is free. How much water can the device produce, and by how much is the salt concentration reduced? Can you figure out ways to make the collection efficiency even higher? This is a great project for inventive thinkers.
Introduction
Nicholas Kinsman is interested in inventing solar-powered devices to reduce our dependence on other energy sources. He's also a winner of a Science Buddies Clever Scientist award for his 2007 California State Science Fair project (Kinsman, 2007). Nicholas set out to build a simple, inexpensive device to desalinate sea water, using readily available materials and easy construction methods.
Typical sea water contains dissolved salts at concentrations between 32 and and 37.5 parts per thousand. That means that if you started with one kilogram of sea water and then you allowed all of the water to evaporate, you'd be left with between 32 and 37.5 grams of salts (also called "total dissolved solids").
With all of that salt, sea water is not suitable for drinking nor for watering most plants. The fluid circulating in your body (blood plasma), contains much less salt than sea water (on the order of 9 grams of total dissolved solids). If you were to drink sea water, your body would actually lose water, because the high salt concentration of the sea water causes an osmotic pressure gradient which drives water out of your cells. Desalination is the process of removing the dissolved salts from water, making it pure enough for drinking or irrigation.
Nicholas's first design for a desalination device is shown in Figure 1. There are eight small bottles surrounding the large collection bottle. Each of the small bottles is filled with sea water. The small bottles have holes in their caps. One end of a flexible straw is inserted into the hole, and the other connects to the large collection bottle at the center. The idea is that the sea water in the small bottles heat up in the sun, the water vapor then condenses in the straws and flows down into the collection bottle. Unfortunately, the idea did not work. You can see in the picture that there is condensation on the inside of the top of the bottle, but there was very little condensation in the straws.