# Evaporation model in ansys Fluent 12.1

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 August 3, 2010, 23:27 Evaporation model in ansys Fluent 12.1 #1 New Member   House xu Join Date: Aug 2010 Posts: 10 Rep Power: 15 Hi, every one, I have to simulate a gas-liquid flow in multi-port evaporator used for automotive HVAC system. AS I found the latest ansys Fluent 12.1 has introduced a new mass transfer model named "Evaporation/condensation model", I set up my problem as follow: Viscous model - Mixture, with consideration on slip velocity. Bubble diameter - for Refrigerant 134a, about 0.1mm Surface tension effect - constant, 0.01 N/m Drag function - Default, S-N model Mass transfer effect - liquid to gas, saturation temperature =8 deg C ,Frequence of Evaporation = 0.1(default) Boundaries: Inlet - velocity (Mass fraction of gas phase is about 10%) Wall in Core area - Constant heat flux Outlet - Pressure ---------------------------- As I read the User guide, I found the new evaporation model is theoretically the same to UDF for mass transfer, while the default coefficient is still 0.1. But the energy conservation is not considered in the new model. That's because when evaporation happened, the quantity of latent heat needed is not known. How can input heat be balanced by the evaporation? ----------------------------- Since there is no heat transfer in the head pipes(tanks), I decide to set the inlet flow temperature to 7.99 deg C, which ensure no evaporation happened there. Then I run the simulation, and get solution converged. ---------------------------- In my results, the volume fraction seems ok, what most confused me is that inlet mass flow rate not equal to outlet one (a big difference, about 50%). --------------------------- So, what's my question are: 1. when use the new evaparation model in Ansys FLUENT 12.1, how to consider the energy conservation. 2. Why the mass not balanced between inlet and outlet while continuity equation is converged well? Where does the over mass come from? 3. Why the default coeff. is 0.1? That mean when local temp. is higher than saturation temp., only 10% liquid flow will evaporate, is it true? Your comments and advices are welcomed. Thanks in advance. chaitanyaarige, ashish mishra and Ahmed Alkaisi like this. Last edited by oldisbest; August 8, 2010 at 22:04.

 August 8, 2010, 22:33 #2 New Member   House xu Join Date: Aug 2010 Posts: 10 Rep Power: 15 No body here has the same problem with me? May be I have to use UDF in simulation. The Evaporation/Condensation model in Ansys Fluent 12.1 seems to be dissapointing.

 September 27, 2010, 14:19 #3 New Member   Join Date: Sep 2010 Location: germany Posts: 20 Rep Power: 15 Hi, unfortunately I cant help you with you problem. But in the near future may be. Could you tell me which chapter of the user guide contains the condensation model? chaitanyaarige likes this.

 October 18, 2010, 15:51 #4 New Member   Join Date: Sep 2010 Location: Germany Posts: 4 Rep Power: 15 Hi, I have a similar problem. I don't understand this evaporation-condensation model completely either, but here is what I have learned: - the model is temp-driven. No temp difference, no mass transfer. - the latent heat is given in enthalpy of the "gas phase"; putting 0 for enthalpy of the liquid phase; use mass-transfer liq to gas (if you are interested in the evaporation, if you are interested in condensation, probably, you have to define it differently). - 0.1 is default and the fine tunning parameter - higher means more evaporation or condensation. --> in my case, I ve notived the mixture temp is higher than temp saturation. Shouldn't it be equal?? something in the energy/enthalpy balance between phases is not clear for me.

 December 13, 2010, 06:00 So evaporation/ condensation isn't properly resolved? #5 New Member   Kamil Sobczak Join Date: Jan 2010 Location: Warsaw, Poland Posts: 6 Rep Power: 16 So this model is unproper? I conclude that mass transfer is calculated with assumption to temperature but my question is that: - do I need define two mass transfer effects liquid->gas and also gas->liquid or only one of them is enough - could energy source described by multiplication of mass released and heat latent be incorporated to energy conservation equation Maybe we could write some udf together for calculation of this? user321 likes this.

 December 13, 2010, 10:23 #6 New Member   Join Date: Sep 2010 Location: Germany Posts: 4 Rep Power: 15 I would not say the model is unproper. There are fine-tunning parameters. It means, if you don`t have experimental data to figure out those parameters, you have to consider the calculated void fraction distribution as qualitative results. The temperature distribution is probably an approximation - check it. As I understand, you just need to define the mass transfer is one direction (boiling or condesation?). The energy source IS described by multiplication of mass released and heat latent and IS incorporated to energy conservation equation. Heat latent is the enthalpy I said you define in the material properties. I don`t know what you could improve by writting UDF???

 September 30, 2011, 10:19 #7 New Member   Jiri Raszka Join Date: Jul 2010 Posts: 7 Rep Power: 15 Hello evreone, one comment abou that. IŽd like to simulate water evaporation with Mixture Elerian model. i can do that but evaporation starst when the saturation temp reaches certain value. if i set ie. 273.15K and temp of air at inlet is 300K then evaporation mass transfer starts at 273.15K Does anyone know how to set saturation temp. For example if i want to evaporate water and ambient air temp is 340K. Because when i set sat. temp as 373K (100C) there is no evaporation. In real life water evaporates even at normal room temperature (i.e. 20C)....ok it evaporates very slowly but with higher temp. higher evaporation. The question how to set it in fluent 13.0?? Tleja, ashish mishra and user321 like this.

April 14, 2013, 22:30
Re
#8
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House xu
Join Date: Aug 2010
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Hi, everyone,

Since my position in company was changed, the simulation on evaporation model was interrupted and became a pending problem.

As some friends are asking me to provide the tutorial and case for their study,
I have uploaded an example of 2-phase pipe flow with the link:
http://dl.vmall.com/c0v5t52aff

I am sorry for late coming back and reply.
Attached Files
 valve.c (2.1 KB, 420 views)

April 16, 2013, 01:22
#9
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Join Date: Jan 2011
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Quote:
 Originally Posted by oldisbest Hi, everyone, Since my position in company was changed, the simulation on evaporation model was interrupted and became a pending problem. As some friends are asking me to provide the tutorial and case for their study, I have uploaded an example of 2-phase pipe flow with the link: http://dl.vmall.com/c0v5t52aff I am sorry for late coming back and reply.

June 13, 2013, 22:44
#10
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Kevin Wang
Join Date: May 2013
Location: Shanghai, China.
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Quote:
 Originally Posted by oldisbest Hi, everyone, Since my position in company was changed, the simulation on evaporation model was interrupted and became a pending problem. As some friends are asking me to provide the tutorial and case for their study, I have uploaded an example of 2-phase pipe flow with the link: http://dl.vmall.com/c0v5t52aff I am sorry for late coming back and reply.

Hi, Xu.
I realise that you upload your files on Huawei netdisk. Are you live in China?
Could you give me you email address so that I can exchange ideas with you ?

 June 12, 2017, 11:46 #11 New Member   Gerardo Ramirez Join Date: Jun 2017 Posts: 3 Rep Power: 8 Have you find how to model this kind of problem? I am working in the same problem

January 10, 2020, 23:43
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user 321
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Quote:
 Originally Posted by Valpress Hello evreone, one comment abou that. IŽd like to simulate water evaporation with Mixture Elerian model. i can do that but evaporation starst when the saturation temp reaches certain value. if i set ie. 273.15K and temp of air at inlet is 300K then evaporation mass transfer starts at 273.15K Does anyone know how to set saturation temp. For example if i want to evaporate water and ambient air temp is 340K. Because when i set sat. temp as 373K (100C) there is no evaporation. In real life water evaporates even at normal room temperature (i.e. 20C)....ok it evaporates very slowly but with higher temp. higher evaporation. The question how to set it in fluent 13.0??
Hi! Could you find a way to perform evaporation below saturation temperature? I am also trying to make a similar model. J would be grateful if you can share any method to resolve this.

 March 26, 2020, 09:11 #13 Member     Angel Penev Join Date: Apr 2016 Location: Bulgaria Posts: 47 Rep Power: 10 Did you find solution?