I'm running a flow analysis of a filter that has several porous media components. The models fine, but now I'm trying to determine the run time distribution (RTD). With a lot of effort in excel I can calculate the RTD using Flow Trajectories, but the Particle Tracking option would be more straight forward. When I try to inject the particles, they seem to get blocked at the first porous media. This is surprising, since I thought Flow Trajectories was a special case of Particle Tracking.