I'm implementing a VOF-DPM model with wo phases (water and air) and solid DPM particles. However I would like the DPM particles flowing only in the water phase, but they go to air too. From the previous comments, you had a similar problem and the solution for that was a UDF. I looked for examples of UDFs for this case, but I do not found anyone. Could you please provide me a example of UDF to limit DPM flow in only one phase or some explanation on how to do that?