[Hamilton]

Hi friends,
In the help of CFX at the Gas-Solid modeling part is stated that water should be selected as continuous fluid and sand should be selected as " Dispersed Fluid " however sand is solid and not fluid , what is the reason ? should we really select sand as a fluid ?

regards

[mauricio]

I'd model it as dispersed solid. You'll have to define the density and properties of the sand material you're going to use. I believe There's actually a tutorial of a dispersed solid and a continuous fluid around it i think.

[Hamilton]

Thank you very much so you think it is wrong ? and it should be dispersed solid ?

[mauricio]

It's not technically wrong for a specific case, check this out from the documentation on cfx's multiphase modelling :

It is possible to model the motion of a large number of solid particles in a gas or a liquid as an Eulerian-Eulerian two phase flow. Examples occur in pneumatic conveying, sedimentation in rivers, and fluidized beds.
For example, the two phases may be Water, the continuous fluid (Continuous Fluid), and Sand, the dispersed fluid (Dispersed Fluid).

In such problems, you should assign the solid phase a small insignificant molecular viscosity. This is permissible, as the physics are dominated by inter-phase drag and turbulence effects. The solid phase should be assigned free slip boundary conditions at walls. If viscosity is not set, the solid material will not be available for selection in the Fluids and Particle Definitions... list on the Basic Settings tab of the Domains details view in CFX-Pre

That would be the case where sand could be treated as a fluid. for other cases, you should set the sand as a particle transport solid, for an example check the tutorial of "Flow through a butterfly valve".