FLUENT - a possible approach to model heat exchangers if fin effectiveness or efficiency is known.
Imagine a fin-to-fin heat exchanger. Imagine two ducts connected to each other by sharing a face wall-1. In the actual model this wall would have fins on both sides. Let assume wall-1 is facing the cold side and wall-1-shadow is facing the hot side. For each side client has effectivenesss e defined as: h_with_fin / h_without_fin. It is the ratio of the heat transfer coefficient with and without fin.
Well, we can run flow and thermal solutions without the fin and get local h_without_fin and its corresponding adjacent temperatures Tcell.
1. h_without_fin needs to be defined using standard wall function for temperature, which requires Tcell or Tp to be the reference temperature. This can be programed using Custom Field Functions (CFF). See the User's Guide for the definition of T*.
2. Run flow and thermal field without the fins.
3. In CFF multiply the h_without_fin that is defined in step 1 by effectivenss to get h_with_fin. Write out a profile of h_win_fin and static temperature at cold side and hot side (wall-1 and wall-1-shadow).
4. Using /grid/modify-zone/slit-face-zone, split wall-1 and wall-1-shadow.
5. Read the profile.
6. In boundary condition panel, for convective heat transfer, apply h_with_fin and Tcell of cold side on hot side and h_with_fin and Tcell of hot side on cold side.
6. Specify porous media to account for fin effects on flow.
7. Run flow and energy.
I did test this on a simpler 2d geometry. The trend was realistic as effectiveness was increased.