Hi, DrAmine Thank you for the reply.

DrAmine-EDIT: removed screenshot from help.

I agree with you that Eulerian wall film model should satisfy my requirement, but it is only available in 3D. The reason I want to do it in 2D is that it could save a lot of computing time in studying the influence of different parameters.
About the reason why I solved particles unsteady and flow steady. this is due to the restriction that the liquid film boundary condition and the particle wall heat interaction option can only be enabled when unsteady was selected for the DPM.