Learning Forum

[Ajayc1160]

Hello allI have to simulate a condensation process on a vertical plate where air vapor mixture at a specific temperature,velocity comes in contact with a wall at a cool temperature and cools down. Is the pressure difference caused by condensation process (due to change of vapor to liquid that causes a decrease in overall pressure of system) taken into account in ANSYS Fluent ?

[DrAmine]

I am not really aware about what you are referring to but if wall condensation is active, so the mixture will lose the vapor content, so the the gas mixture molecular weight will increase (wet air is lighter than dryer air) and this will definitely affect the pressure. We are solving standard conservation equations for energy and components and the condensation along the walls can be tracked by a wall film model.n

[Ajayc1160]

How to identify if only wall condensation happens or bulk condensation happens ? Is it possible to include both wall and bulk condensation in ANSYS Fluent? n

[DrAmine]

Yes it is possible. Bulk is far away from solid surface like water vapor condensing in wet air mixture (like rain) however heterogeneous nucleation does require nuclei.nnIn your case condensation occurs at wall surface.n

[Ajayc1160]

In my process there is a vertical plate whose left side acts as inlet for mixture of vapor and air to come in at a specific temp, comes in contact with the wall at right hand which is maintained less than dew point . The other parts of the vertical plate are adiabaticnSo I can use the wall condensation model in ANSYS CFX or EWF in ANSYS Fluent to setup this condensation process ? Is it incorrect to use the VOF or Eulerian mixture model to simulate this process?n

[DrAmine]

Not incorrect but you need to account there for wall condensation. For that reason use EWF model in Fluent or CFX model if only condensation.n

[Ajayc1160]

Following is a setup from my simulation I am trying to simulate condensation of air and water vapor condensation in following domaiFor this I created a mixture of vapor/air using species mixture, created a seperate liquid phase, used mixture homogeneous model (water vapor,air) with Lee condensation model . The oprating pressure is 12500Pa.At this pressure, sat temperature is 50C-55C. So condensation should happen in the model . However in the following results even after running for 1200 iterations, I still dont see major changes in volume fractions of vapor/air and liquid. However I do see mass transfer contoursnnMass transfer rate contoursnn nnnVolume fraction contoursnnnI know that I havent accounted for wall condensation in the model but even in the bulk i cant observe any condensation happening. Also the volume fraction contours dont even change even though I ran the simulation for 12000 iterations. Time step size is 0.0005nn

[Ajayc1160]

Hello Dr AminenI have a question about defining two species mixtures in ANSYS Fluent. When I define liquid as a species mixture, its properties are calculated based on gas EOS. Is it not possible to define a mixture of two liquids ?.Also is the mass transfer UDF in ANSYS Fluent customization manual defined for two mixtures in the simulation?n

[Rob]

It is, but the mixture properties tend to be mass or volume weighted average. Check the species properties in the mixture. n