Arun mathew

Thank you for your reply. I apologize for not explaining the problem clearly. Please forgive me for any confusion caused.

Let's simplify the problem to water diffusion through a porous medium. Suppose there is a pipe with insulation covering exposed to atmospheric conditions. Due to the condensation of water vapor on the outer layer of insulation, water is deposited there. The water then diffuses through the porous insulation layer and reaches the outside of the pipe. I would like to know the water content present at the outer surface of the pipe.

There will be a definite flow through the porous layer, but I am unsure whether it will be single-phase or multiphase flow.

Let's assume there is a certain quantity of water per unit area on the outer side. I would like to know what kind of inlet boundary needs to be applied.