I am looking at Particle Transport models in the CFX Solver Manual and a question has arisen: under "INTEGRATION PARAMETERS" command in the command file, we can set these options: COEFFICIENT OF RESTITUTION and KEEP PARTICLES OFF WALLS. My questions are: 1. Which are the differences between both options? and, 2. Is it possible to set both options at the same time? (It doesn't seem to have sense). Thank you very much.

There are different. If you set the coefficient of restitution to zero,the particle will keep in wall but not stop calcution the particle,it's only keep in the wall.If the coefficient of restitution to 1,all particle will bounce after meet wall. but if your set the keep particles off walls.the particle track will stop to calculate after meet the wall.This is the different between these command. Of couse.you can set it together. But some time it's not very accrute.