Help with Evaporation rates for school project

JoshHarpst

JoshHarpst

New member
Hello everyone, my name is Josh Harpst (if you couldn't figure that out) and am in my 6th semester at slippery rock university. I am a Mathematic's major and just got an invitation into KME (Kappa Mu Epsilon) the national honoray Mathematics fraternity. To get inducted you must do a research project and i thought, hmm, with all the time i don't have what can i do? So i decided that i wanted to have it deal with something i am passionate about and that just so happens to be Saltwater Aquariums. Well the project has to deal with math so i decided i wanted to do research on Evaporation rates due to temperature in the saltwater aquarium. This will involve differential equations and such so it's mathematical. So what i need your help with is some information. Any sites or anything that deal with evaporation. The mission of this research is to model an equation that can help predict the mean rate of evap due to temperatue so that way aquarists can calculate the amount of water they need to drip into the system while the water is evaporating to keep salinity stable. Any help or motivation would be greatly appreciated. I have just started this reseach today and the project needs to be completed by April 10 to be inducted. So thanks in advance and hopefully i'll get this thing running. Thanks everyone.


~Josh Harpst
 
Interesting subject. Wouldn't the evap rate also be affected by open surface area of the tank and sump, room size, room temp, time of year, etc?

This could get complicated.
 
correct, my research is going to deal only with the variables of surface area and temperature. You are correct, there are TONS of variables, which i may include more, but for right now i'm only going to deal with the temp and SA. By running a fan across the top of the water you increase the evap rate by three or more times so i will not be interested in that. Thanks


~Josh
 
Relative Humidity is just as important as temp imo. If you don't have a controlled environment, the study will be meaningless. If your study compares evap rates based on temperature and SA changes only...All other variables must remain constant
 
well your tank is always evaporating....at a lot higher than your water loss too. But some of that water that is evaporated is recondenced. there is a lot of factors in how this happens.....
Exposed surface area
Temp of water
Temp of Air
Air vapor pressure
(you can combine the temp of the air and the vapor pressure to get realiztive humidity)

You will also have to make some asumptions, for example that there is no glass hood (thus causing increased humidity above the water and thus lowering evaporation)
And you will also have to assume there is no fan or air movment around the surface of the water
Another thing you have to assume is the surface area of the sump is at the same elevation as the tank top.....this is because as you decreased in height your temp decreses due due to increased air pressure, and your vapor pressure also increases at a diffrent rate. Although these diffrences will be slight it is an assumption you must make.

There are a lot of factors in this and it is going to be pretty tuff to get a semi-accurate function that is just based on temp surface area, and Relative humidity (the combination of air temp and air vapor pressure).

hope that info helps you out

edit** also you MUST include realitive humidity because this is the biggest factor. If your RH is 100% you will get NO evaporation. so thus it will be very very dependent on RH. Anything you produce that does not take this into consideration would be next to worthless in real life.
 
I think relative humidity and ventilation will affect the evaporation much more than water temp. Actually, I would think the water temp would be insignificant unless you are comparing water at 2 celcius to water at 95 celcius
 
thank you very very much, that really helps. There are going to be a lot of things i think about before i jump into this and your info definately helps.

~Josh
 
My tank is kind of extreme for evaporation. I live in Arizona so very low humidity, and I have a fan blowing over my sump.

I evaporate about 6-7 gallons a day
 
Consider that heat is also a function of the rock in the tank. I noticed this when I switched to Halides....
...the rock in the tank absorbs heat during the day and when the lights go off, they slowly release the heat into the water.

IMO, doing a research project using SA and temp as your variables is gonna be difficult. You'd require a constant relative humidy for all these experients. The only way to do that would be to run all test cases at the same time, in the same room.
 
This site doesn't address quite what you're looking for, but they may have done some research into the matter or at least be able to give you some advice.

http://garf.org/

What they have is a calculator that will tell you the salinity change given a certain amount of evaporation. They do a lot of research, though, so I bet they'll have some useful info if you contact them.

As for factors, I'd agree that humidity is a huge factor. If it's a particularly humid day, I have significantly less evaporation in my aquarium, and that's with the A/C keeping a fairly constant temperature, same lighting schedule and same powerhead configuration, so I see humidity as the biggest variable there.
 
well i have a 55 gallon tank, completely open top, 260 watt PC's at a constant 78 degrees (NEVER fluctuates) Room temp is consistantly in the mid - high 60's.

i lose about 1.5 gallons a day (i refill with 5 gallon bucket every 3 or 4 days...

good luck.. sounds fun... if a weird math way.. lol :)
 
dont you also have to take into account the composition of the water after some evaporation has already occured?
 
thanks everyone, i appreciate all the help. I'm not sure anymore if i'm going to go after this as my project now since there are so many variables that the research would almost help no one so i've gotta figure out another math project with SW aquaria. Thanks for all the help and if you can think up an idea, let me know. Thanks again

~Josh
 
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