Evaporation calculation

[paulistadecongo]

I'd like to be able to calculate evaporation rates for a settlement pond in an arid environment.

Does anyone have an excel calculation sheet?

 

[MEM1]

We do overnight water balance tests on ponds. The methods and equations can be found in Jay Ham's research paper. The evaporation is calculated using the bulk transfer equation. Do a google search for overnight water balance test. That should bring it up. The calculations are done in our data collector so I can't help you with a spreadsheet. I can tell you this isn't as simple as it may seem. Evaporation is dependent on weather data and water surface temperature and is highly influenced by wind speed. The higher the wind speed, the more error there is in the evaporation calculation. This is why we do the tests overnight as wind speed and air temperature are typically low enough to calculate accurate evaporation.

 

[bimr]

It is probably too complicated to calculate the evaporation rate. It is probably preferable to use long term rates from standard evaporation pans to make rational evaluations of pond evaporation,

The evaporation rate is influenced by

1) Temperature of the water at the air-water surface.

2) Humidity of the air.

3) Area of the air-water surface.

4) Air temperature.

5) Water currents that convect heat through the water depths.

6) Wastewater parameters.

7) Airflow rate past the water-air surface.

All of these paremeters are continuously changing so I is difficult to come up with an "evaporation rate".

 

[hydrae]

As I remember from my third year Engineering classes, third term as Mechanical, we had a course titled "Heat Transfer", which followed Thermodynamics 1 and 2. Extensive time was taken on convective heat transfer both natural and forced, as that is one of the more complex equations in the class. Close to the end of that segment, it was noted that mass transfer uses the same equations as convective heat transfer, but you have to add in the heat of vaporization when dealing with an evaporating fluid, so you run the same equation twice in parallel doing a heat and mass balance.

Do you have access in your office to a Mechanical Engineer who may be able to pull up a Heat Transfer Text?

Hydrae

 

[gbam]

Man, its been a while. Check the USGS or BLM for pan coefficients for your area of interest. Either of the two Agencies may even have average monthly evaporation. In Arizona the annual average is 7-feet +/- with the peak in June of 3 or 4-feet (cant remember). Google your area's evaporation rate and you should get some hits.

 

[paulistadecongo]

Thanks for the input guys. My arid environment is NW Western Australia but I'm sure the US references can be converted.

Unfortunately I don't have a Mech Eng at hand. I'll chase up the avenues and hopefully it will work out!

Cheers

Paulistadecongo

 

[fel3]

A quick Google search for Australia evaporation pan coefficients turned up these interesting documents, among many others:

http://archive.agric.wa.gov.au/objtwr/imported_assets/content/lwe/water/watstor/tr065.pdf?noicon

https://www.longpaddock.qld.gov.au/...tralianSyntheticDailyClassAPanEvaporation.pdf

http://www.mssanz.org.au/MODSIM07/papers/10_s61/EstimatingEvaporation_s61_Johnson_.pdf

http://www.hydrol-earth-syst-sci.net/17/1331/2013/hess-17-1331-2013.pdf

As well as this site that looks like it might help:

http://www-das.uwyo.edu/~geerts/cwx/penpan.html

Here in the central San Joaquin Valley of California, our evaporation rates are not much less than gbam mentioned for Arizona. My swimming pool seems to evaporate about 0.5" to 0.75" per day in the hottest parts of the summer.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[cvg]

pan evaporation in the lower desert regions of arizona could easily be much higher than reported above, up to 140 inches per year. Tucson is approximately 104, Yuma is much higher