Hi: My particle is 1cm diameter and my tube is 5 cm diameter , I think particle scale is big for my tube. I think have two way to simulate it. 1. Solid and liquid flow in moving mesh ? 2. I use Langrange particle to simulate particle flow in fluid? What is correct way to simulate big particle?

(1). Looks like that it is too big to be a particle. I would say that it is a sphere or a ball. (2). You can try to fix the coordinates system to the sphere, and assume that its position is fixed relative to the tube. In this way, you will be able to compute the flow with moving tube wall boundary (relative to the shpere). (3). This is the only way to comput the flow field around the shpere in a tube. If you allow the sphere to move around in the tube, then you need to determine how the sphere should react to the flow field. This will become a very difficult problem to solve.

Hi: Thank you for your suggestion . I have many sphere flow in tube, I want to get sphere 's residence time. Is it suitable to simulate it in DPM model in FLUENT 5.5? Thank you very much!!!