Thank you very much Rob for your fast reply. 

Is there any way to eliminate this since it introduces high errors in calculating particle size distribution or total particle mass along the tube? 


Another question is, what happens to the particle ID if Ansys tracks the same particle that passes the plane (whether it is the first time, second time, or tenth time)? Does it give a new unique particle ID to each particle that passes the plane? Or the particle ID will be the same?