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Q & A: solar desalination

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Most recent answer: 08/23/2011
Q:
Is there a chemical (or a chemical reaction that can be initiated) that can be added to high saline brackish water which has the affect of accelerating the rate of evaporation? My daughter is wanting to build on her science project of last year which studied solar desalination of sea water to see if she can increase the rate of production of solar desalination of contaminated groundwater. Thank you.
- scott kuney (age 55)
bakersfield california, usa
A:
I don't think that there will be any ways to get a major speed-up unless the original apparatus was especially inefficient. Here's why.

To evaporate a given amount of water, something must supply a fixed amount of energy, determined by the latent heat of vaporization, basically to pry the water molecules loose from their neighbors. Presumably in your solar system that heat is mainly coming from the sunlight. I guess the water gets pretty hot, so you could be losing some heat to conduction through the walls of the container. A bit of thermal insulation should handle that. Once you're sure that almost all the sunlight is being absorbed and that not much heat is leaking out, you should get  almost 1 kg of water for about 2.3 MJ of sunlight energy in.

Mike W.

(published on 08/23/2011)

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