Thank you DrAmine for your answer. I have attached the full computational domain. Wind duct is the fluid domain while fins and tube are the solid domains. If I make tube and fins one combined solid domain then Ansys creates connections between wind duct and fins/tube automatically. I also tried splitting fins and tube while making them two separate bodies then connection between fins and solid was only created. Both are not working though. I am inexperienced when it comes to interfacing. Could you kindly elaborate more on this problem Please.