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-   -   Mixture model - water droplet + air - EVAPORATION (http://www.cfd-online.com/Forums/fluent/47131-mixture-model-water-droplet-air-evaporation.html)

bohis January 25, 2008 07:19

Mixture model - water droplet + air - EVAPORATION
 
Hi, I have the water spray in an ambient atmosphere and an evaporation takes place. How should I solve it? UDF via source terms or some kind of species? I do not know,

please, give me any advice! Thanks, Jack

Jean-Marc Vignon January 25, 2008 11:04

Re: Mixture model - water droplet + air - EVAPORAT
 
I think I've the same problem. I try to calculate a simple axisymetric spray of water in air. I use the Discrete phase model, but for the moment I fail to enable a thermal interaction between dropplets and the air. the species transport equation seams to be without evaporation, and the energy equation don't operate : if I assume a temperature to injected droplets near 373 K, with air at 300K, I have been unable to see any effects. I used several mesh, and finally, I use a 2D mesh, just for testing models, before to incorporate the adequate settings in more complete model. The answers to your problem interest me, and I'm sorry for not helping you.

bohis January 25, 2008 11:14

Re: Mixture model - water droplet + air - EVAPORAT
 
never mind, thanks for your interest

I think I will use mixture model - simple (higher probability of convergence) I will use some UDF for mass source and energy, but I am not sure about momentuum source.Probably, I will neglect it I cannot use DPM because in my case water poses as continuous phase as well

what do you think about my suggestion?

thank you, bye, Jack

Jean-Marc January 25, 2008 11:43

Re: Mixture model - water droplet + air - EVAPORAT
 
I believed that mass and energy source was available, and it seems that not. For momentum source, it's included, and it's the only function describing the interaction between the dropplets of water and the surrounding medium. I have seen some problem of stability or convergence, giving sometime velocities in the fluid higher that the dropplets. There is certainly some ways as you do to overcome the problem, but I will insist. I think that it is important to handle this problem : it's the basis of any spray. How can I trust the sofware for combusting spray if I can't test a simple (and refreshing !) spray of water ? May be I will ask to the staff of Fluent, if a don't find somebody having solved this problem. I never used UDF, being a beginner with Fluent : may be it's the good approach. Bye, Jean-Marc

bohis January 25, 2008 12:04

Re: Mixture model - water droplet + air - EVAPORAT
 
okay, I think, firstly it is important to understand basic principles, to keep in mind your simplifications, but use them! Anyway, it is very often necessary to use UDF, which can help you to approach more to your specific problem

bye


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