I'm running a Lagrangian particle tracking in a flowing system where there are one inlet and two outlets. Solid particles are injected at the inlet, and I would like to know the concentrations (g particle/kg fluid) of both outlets. Every time when I vary number of positions, I get different concentrations at the outlets. Is Eulerian-Lagrangian model suitable to monitor concentrations? Or Eulerian-Eulerian model is more suitable for this case.

For any time, if you run for the problem with the Praticles you have to run the problem with Eulerian-Lagrangian model only. Then only you will get the correct results. Eulerian-Eulerian model is only for the multiphase analysis with completely mixed fluids , not for the solid particles or liquid droplets. In your problem, Yes definetly concentration will vary from location to location. Why because its not a homogenious mixture. Depends on the requirement you have set the location to be fixed. most of the cases its at exactly outlet. I think you got it...

Thank you for your reply. I now realize that the location of injection has a significant effect on where the particles are going to end up. I know that Eulerian-Lagrangian model allows us to see particle trajectories. It, however, predicts only a small fraction of total particles. Therefore, we must make sure that the sample of particles being modeled is representative. In my system, one outlet is much larger than the other one. Do you think Eulerian-Lagrangian model is also good for quantitative analysis, such as to determine concentrations in each outlet?