Calculating Heat flux
 

Hello everyone, I am currently haveing some trouble getting my head around somthing, and would appreciate some assiatance. I am trying to create via a UDF the same conditions that are used in the "coupled" wall boundary condition for heat flux from solid to fluid. I tried passing temperature from on side to the other, but that didn't work (I suspected it would be too easy). Dose anyone have any help with this one? I found this in the Fluent manual, but it didn't make much sense to me:

qid = cid[0] + cid[1]*C_T(c0,t0) - cid[2]*F_T(f,t) - cid[3]*pow(F_T(f,t),4)