So, what you reached is a conclusion ... all the particle got trapped in the first section of the tube which could be returned to the centrifugal force. But you need to confirm this conclusion. Use lower density particles and see if they can go further. nOr, make another injection somewhere after the nozzle, and you should see the particles getting trapped after few meters as well.nnProbably injecting particles that have density very close to the fluid would do what you want. Try! n