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Why does fresh water evaporate faster then salt-water?

How fast does water evaporate?

  • How fast does water evaporate? Let's say I have a huge tract of land and I want to cover it with water to evaporate the water. Is there a formula relating air temperature, humidity, and stuff like that to show how fast the water will evaporate?

  • Answer:

    I didn't realize just how fast water evaporates until I put two fish tanks into our bedroom to give us some 'humidity' in the air. I have one 20 gallon tank and one 45 gallon tank. I have to ADD at least 3/4 of a gallon to the larger tank every two days, and the same amount to the smaller tank every four days. The smaller tank has a 'smaller opening' so the water doesn't evaporate as fast ... but perhaps the amount of water I must replace from each of those two tanks and the number of days between each 'replacement' will give you the 'formula' you need to determine the 'evaporation rate' ... the 45 gallon tank is a 'normal' size, the 20 gallon tank is a 'long' tank, not a 'tall' one ... go to any pet store and measure for the 'opening size' of both.

water_sk... at Yahoo! Answers Visit the source

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Don't know if this will help or not , I found some info on swimming pool evaporation rate ...might would work. http://www.thermexcel.com/english/program/pool.htm

J M

Evaporation rates depends on the volume to surface area ratio, temperature, and quiet or moving pool. There are specific evaporation formulas, but they are complicated. I did however find a simplified version of the equation. A high school science project. I'm not sure how accurate it is. E = - rho * L * k * ustar * (q2-q1) / ln(z2/z1) where E is evaporation, rho is air density, L is the latent heat of vaporization, k is von Karman's constant, ustar is the friction velocity, (q2-q1) is the specific humidity difference between the air and near the water surface, ln is the natural log, z2 is the height of the dew point temperature measurement, and z1 is a height near the water surface.

The evaporation rate will vary as the temperature varies (eg. midday is the highest rate, nightime there's hardly any, boiling water will evaporate faster than cold water). I'm sure there's a formula somewhere, try some hydrology websites maybe? You may also need to account for the infiltration rate into the soil.

violet

Here is a practical way to solving your dilemma. If your huge tract of land is irrigated and you want to maintain the level of the water, just make up for the loss due to evaporation by pumping more water. You may need to do this quite often during dry season (summer time). You do not even have to worry about making up and maintaining the water level during rainy season. Once your huge tract of land is saturated with water, evaporation will hardly take place when the crop is already growing. It looks like you have rice paddies and wanted to maintain the water level of your rice fields which is the only practical application of your question. Rice farmers do not worry about what type of formulas to use. They are not engineers, chemists or physicists. My Dad had rice fields and never ever bothered to ask for such formula. Hint: Evaporation takes place at any given temperature (cf. Physical Chemistry Textbook). Good Luck!

ATIJRTX

Yes there are formulae for these, you will need to find them in chemical engineering textbooks. The rate of evaporation depends on temperature, air humidity, air movement and of course the surface exposed to the air and the size of a container that the water is in. You don't have a container so that variable is eliminated. The field of engineering is called psychrometry. There is a Wikipedia article at http://en.wikipedia.org/wiki/Psychrometry

Brigalow Bloke

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