hi,all I have trouble to define an outlet of gas-solid two phase flow, which gas phase can pass through while solid phase can't. How can i achieve this.

I assume that you are talking about an euler-euler solution. I had a similar problem once (in CFX4.4), I think I solved the problem by setting ambient conditions for the solid phase to zero and solved the problem as transient. (I had to solve it transient because I only had one outlet and the solver will try in a steady state to equalize inlet-outlet.) Hope it helps

Thank you for your suggestion. you are right, i am talking about an euler-euler solution and my problem is similar with the one you once meet. But my problem still remains. My problem is as follow: Gas-solid flow goes into a tank through an inlet and there is an outlet which only gas can pass through. so the solid remains in the tank. But i do not know how to difine such an outlet in CFX4.4. I have tried several times with different method. 1. I define INLET and MASS FLOW BOUNDARY as the inlet and outlet and define the flux of the MASS FLOW BOUNDARY as 1*1.0 and 1*0.0. The result is both gas and solid phase pass through the MASS FLOW BOUNDARY. 2. I define PRESSURE and MASS FLOW BOUNDARY as the inlet and outlet and define the flux of the MASS FLOW BOUNDARY as 1*1.0 and 1*0.0. The result is no solid came into the tank through the inlet. 3. I define INLET and MASS FLOW BOUNDARY as the inlet and PRESSURE and define the normal velocity of the oulet as zero by using USRBCS. The result is both gas and solid phase pass through the MASS FLOW BOUNDARY. 4. I want to define the outlet as Porous walls. But I do not know how to define.

Best regards!