hi,everybody,I am trying to simulate the condensation process of the vapor passing through a pipe with a cooled surface. And now I have several questions to solve: 1.which model is more suitable for this case? 2.Need I define the UDF for mass transfer if I choose the VOF model? 3.Any else points I should pay attention to during the simulation? Thx in advance!!

Tony

here is some anwser: 1. depends on what your are looking for.

2. Yes you need to define a UDF. 2 possibility.

a- you can reproduce the TUTORIAL on BOILING and modify the UDF for condensation application.

b- Use a define exchange property for the mass transfer and put in the right standard state enthalpy in the material panel to simualtion the energy through the interface due to latent heat..

3. IF you use VOF use (PISO / PRESTO). Prefer a hight number of iteration per time step (100) rather than checking residuals convergence criteria.

Hope this help. THomas

Thank you very much,Thomas! Now I am using Fluent 6.1 to simulate the problem.And I still have several questions to slove,so I hope you can help me again. 1.As I described in the first message, the vapor passing through the pipe with a cooled surface.I am wonder whether the value of the volume fraction of the liquid in the initial panel will influent the result.If does,how should I set up the initial contidions? 2.If I want to simulate the process of the condensation and the energy exchange during the process, which model is more suitale? 3.the standard state enthalpy you referred to represent what physical meaning?and what value is proper?? Thank you very much ,if possible I hope we can discuss the correlative problems by email or msn messager my email address:twhitecat@msn.com

tony