Back flow issue in triangular duct
I am trying to simulate a PCM-Water hybrid system. One of the pipes contains PCM, while other pipe which is interacting with first one has water flowing through. Heat transfer is taking place from a face of PCM-pipe to PCM and then to water. When I simulate the individual systems, that is, PCM only and water pipe only, in transient state, and all settings same, it works fine. My PCM melts completely, and my water reaches a steady state. But when I combine the systems, and have both of these in same model, I am facing an issue of back-flow, right at the beginning, and it cant be ignored as it goes to about 20-30% in just a few iterations.
I am using SIMPLE model , and have adaptive time step method for calculation. My mesh quality is fine too. What could be the reason for such an issue.
Thanks and regards,