Thanks for the prompt reply, that means I need to have a very small volume near the porous surface cells. dpm particles are raindrops of diameter 3-7mm. Lets say the cell size around the surface is (0.05*0.05*0.01) and the volume of single raindrop of 3mm has volume of around 1.15e-8, then the volume fraction should alteast be around 1.15e-8/(0.05*0.05*0.01) = 4.6e-4. Is that enough? and also if I need to do it, what is the procedure. I know how to convert dpm-to-vof using water film and checked it through the contour plot for vof for phase2(water). However, I am not able to convert them directly without any surface contact.