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Linjie May 22, 2007 17:10

Water Evaporation and condensation modeling
Hello everyone!

I am doing a project that will require an emulation of water evaporation and condesation in a enclosed glass box structure (measures 4x20 meters) with a thin layer of water (0.3-0.6 meters deep)laying at the bottom of the container. Physicaly, the water will start to evaporate when the sun hits the water and raises the tempature, while the evaporated water vapour (gas) rises to the ceiling and subseqently condensate into liquid water when reaches dew point. The question is if the measurements of the glass box and the volumn of the thin layer of water and the air temperature outside the box is given, how can i model the evporation and condensation process and phenomenon? (either in CFX or Fluent) Since I am a total beginner, please be simple and step by step if possible, or if there is any example or tutorials exist somewhere, please let me know!!

thanks a million!


Gert-Jan May 22, 2007 18:27

Re: Water Evaporation and condensation modeling
What is the question you want to answer using CFX or Fluent.

As a total beginner I would not start with CFX or Fluent. Start with general engineering calculations. Light radiation, emissivity, temperatures, evaporation model, flow. Quite complex, not easy for a total beginner...... Where to start? I would ask a colleague, CFX-support, or hire a specialist if you have the money.


Linjie May 22, 2007 18:46

Re: Water Evaporation and condensation modeling

Thanks for the quick response. I have done some small scale working models to test the evaporation and condensation and I did all the manual record of the temperature, humidity. They all worked fine. However, I need to test the same phenomenon will happen in a larger scale construction and if different, how i would be able to improve it. which will inevitably requires the computer simulation. What I really need now is a bit of technical support of the CFD programs. I've gone through some of the related posts here and found my case is relatively simple, could you give me some hint? Thanks again!


Linjie May 22, 2007 18:50

Re: Water Evaporation and condensation modeling
Or some articles or tutorials you would recommend, that would be also helpful!! cheers Linjie

Joe May 23, 2007 04:52

Re: Water Evaporation and condensation modeling
It would be difficult to capture that sort of process in its full complexity using CFD.

An analytical model would give you plenty of scale-up information. Do that first before you think of CFD and then only if CFD will actually give you useful additional information that is worth the considerable additional effort it would require to develop the CFD model.

Further, a dimensional analysis of the design and constructing a somewhat larger second prototype would give you additional insight into the designs scale-up behaviour.

Gert-Jan May 23, 2007 08:41

Re: Water Evaporation and condensation modeling
What to do with the sunlight? You need information about where it is absorbed. On the outside of the glass of the green house? Is it absorbed by the condensated droplets on the inside of the glass? And how much? The remaining light will be partly absobed IN the water, partly it will be reflected. A problem is also that CFX does not have a standard framework to model light as it is different from heat radiation. If have done some test for UV light using a heat radiation framework.

Perhaps you can simplify things by ignoring all the light radiation and defining an energy source at the water surface. The source should contain an constant adding term for the radiation and a variable negative term for the evaporation. The evaporation rate will be a function of temperature. For the evaporation and condensation of water standard models are available in CFX. Just use such a framework as a start.

Good luck, Gert-Jan

Linjie May 24, 2007 14:55

Re: Water Evaporation and condensation modeling
Thanks Joe and Gert

I will have a look into it, honestly its rather complex than I initially thought!

Cheers! Linjie

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