How can I get a variable expression from another module?

Hi, I am working on a evaporative cooling in porous media model by using chicken patties and evaporative cooling model as a sample. My work consists of 2 module Transport of diluted species and heat transfer. I try to combine the concentration at porous surface with concentration lost per uint time so I want to refer inward flux in transfer module to heat flux in heat transfer module in this following equation D_m*lda*cr+h_T*(T_air-T) , I will refere mass lost per unit time insteat in D_m. What expression variable I should refer to and how can I find another expression if I want to? or anyonr have any suggestion about my work.
Thank you.