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Q & A: Evaporating water chiller

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Most recent answer: 10/22/2007
Q:
If Considerably low pressure is maintained is maintained in a box with the help of a vaccum pump, and water is made to evaporate as in a Air Cooler. How much evaporation can be expected or how much cooling can be expected inside the box? Make any assumptions about the initail temperature, and pressure inside the box.
- issa (age 34)
Pakistan
A:
Hi Issa,

There are quite a lot of variables which affect the cooling rate. The vacuum pump, if a good one, will be able to remove the water vapor very nicely, and if it can get the pressure in the box below the vapor pressure of the water at the temperature at which this is operating, then the water will boil. Then it is just a question of how fast heat can be transferred to the box. It takes 540 calories per gram of water to make it evaporate, and at low pressure, if the water doesn't freeze first, it will all evaporate eventually. I'd say that with an efficient refrigerator such as this, you will be able to get quite a lot of cooling power out of it, but it depends on the thermal conductivity of the box and the temperature outside and how it is operated.

One thing that can happen -- The water may partially freeze, keeping it from boiling, and this may reduce the rate at which the device can cool something else, because a lot of the benefit of convection is gone.

Why don't you try it?

Tom

(published on 10/22/2007)

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