Hello. I am trying to model a shell and tube heat exchanger with PCM filled in the annulus and heat transfer fluid flowing inside the inner tube. There is also air existing at the PCM side, so I turn on the VOF to solve this side with mixture of PCM and air. The problem is that when I want to define the HTF in the inner tube as a single phase (water) fluid domain, Fluent regard it as mixture of two phase (PCM and air) . What should I do? Do I have to write UDF to solve this problem?
Dear Wenwen Ye,
Did you try setting up a third VOF phase that is not used on the pcm side but only on the htf side? You could set the pcm and the air phases to zero then on the htf side. Not sure if it works though. I guess the problem is overly complex. I would try to focus on the pcm side and model the htf side only with a quasi stationary convective boundary condition. That resulting problem is challenging enough. Good luck and please keep me posted about your outcome.
Best regards, Julian
Dear Sir,
Thanks about your suggestion. I have thought about defining the inner fluid as the 3rd phas, but the inner fluid does not contact with the PCM and air. I am not sure if it make sense. I will try to run it to see whether it will give me a good results. Another thing is that if you apply a heat transfer coefficient as a boundary, It seems that you are solving two sides separately instead of a coupled problem.
Thank you.
Three phases should work, even if they are not in contact. But sure, you'll have to try.
You're right, if you set constant boundary conditions, you won't solve a coupled problem. However, you can calculate 1D temperature and heat transfer coefficient in a udf depending on your fluent solution at the inner tube boundary and then use the calculated udf boundary conditions for the solution. This would give you the coupled solution.
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