Thank you for your nice comment. nI liked your idea of trying with the (1) density close to fluid, (2) another with low velocity.nI was using same velocity (4m/s) for both fluid and particle. I would like to perform a trial injecting them with a lower velocity . To inject the particle at the pipe center line, Is there any specific option on the injection dialog box ? or do i have to edit my CAD model of Incoming flow region . I was just using a 1m long cylinder tube as my incoming flow region. nThe upper one is I was using .nnhow about this to make a separate inner tube having a small diameter for the particle injection with in a tube, to inject the particle at the pipe center line?nnnThanks in advancen