Thank you and Appreciated for your Helpful Comment.nI reviewed the user guide and watched some tutorials and got idea about injecting the particle with actual timestep necessary to fill the section of the pipe.nI tracked the injected mass vs flow time in one plot window and Escaped mass Vs flow time in second window............and so on until 10 monitor.nnI have setup the all of my long tube wall condition to trap. Now Here is what I wanna do. nI tracked the mass of the particle need to fill the section 1 and I ran the simulation until that specific number time step to fill the whole first section of the tube which wall condition was set to trap initially.n I am having this problem:nNow I want to turn the wall Boundary Condition of section-1 to reflect to let the particle move to section-2 (wall condition: trap) and run the calculation with enough number of time step. nHow Can I do this to continue the cycle of moving the particle from sec-1 to sec-2? I tried without initializing the setup but the particle are not reaching section 2. I am not getting any plot data(Escaped mass Vs Flow time) that I setup for section 2 .nIsn't particle supposed to move from section-1 to section-2 after changing the sec-1 wall BC to reflect ?.nCan Somebody help me on this ? I will really appreciate thisnnThanks