Thank you for the reply. In fluent I have the wall between fluid and solid as coupled walls. Picture attached. I have no option to select the 'via system coupling'. What must I do in this case? 

I had another question. My ultimate aim to build a system coupling involving ANSYS explicit and fluent. But in ANSYS explcit I do not see any option to create a 'system coupling region'. This option is available in transient thermal and steady state thermal. Does this mean system coupling does not work with ANSYS explicit? 

Thank you for the support.

Ibrahim Nouzil