Problem: I am trying to model two phase flow using FLUENT multiphase model. There are two parallel channel with a shared wall between those two channels. There are heat transfer through this shared wall. I defined liquid phase which flow through one channel as primary phase and gas phase which flow through another channel as secondard phase. First, i apply the mixture model to iterate some steps and then i apply the Eulerian model to iterate for hundreds steps. After iteration, i check the pressure distribution and volume fraction distribution. I have several questions.

(1).I found pressure at liquid phase channel is fine, but pressure at gas phase channel is too large to be true. For example, the gauge pressure for liquid phase channel is zero Pa, but for gas phase channel is 2.0e+6 Pa. The pressure should be similar and not supposed to be that way. Do you know what is the problem and how to correct it? (2). I found that the volume fraction of liquid phase (primary phase) at gas phase channel is quite large (0.3-0.9) even though i only define gas phase flow through the gas phase channel. The volume fraction of liquid phase at gas phase channel is supposed to be zero. Do you know why it is not zero and how to make it be zero. (3). Based on the problem i described above, do you have some suggestion or other way to solve my problem?

From what i understand from your message the fluids are not interpenetrating? If this is true you can define either side of the shared wall as two seperate fluid zones using gambit. This way you can use a different fluid in each zone and also make multiphase model obsolete.

if these two fluids are not mixing, define them as seperate fluids. no need to go for Multiphase Flow.

Mahesh, thanks. Could you explain how to define them as seperate fluids instead of multiphase flow? In my understanding, if i want to define gas phase in gas phase channel and liquid phase in liquid phase channel, i have to invoke the mulitphase model. Otherwise, fluent will only assume there is one phase existing in systems.

You will have two different FLUID panels, one for gas and other for liquid. For GAS select material as "GAS" and for LIQUID,select the material as LIQUID.

Hi,mahesh Thanks for your response,but i still can not get it. My confusion is if i do not invoke the multiphase model, only one phase is assumed in Fluent. Actually, there are two phase in different channel. How to define those two different phase in FLUENT without invoking mulitphase model? Could you explain by detail? Thank you very much.

hi.you know i'm workin on exactly the same case and if you seperate the fluids in Gambit then in Fluent in matterial pannel you should add the for example water to your working fuid.and you can describe each of them in case of their own properties.if there exist natural convection you need to use one of the two methods (bossinsq or polynomial) for density.mean while you would need to secify the operating density for reference density which here the problem looms.you can not specify two reference density for the both your fluids.but try this method.maybe you solve your problem. good luck