Multiple flows
 

Hi all,

I want to simulate the following scenario (attached as a picture):

Water vapour and air enters a chamber through two separate inlets, and a mixture of water vapour and air exits a single outlet. I want the simulation to help me determine how much of the exiting flow is water vapour and how much is air. From laboratory experiments, it was found that the air flow is not enough to push all the water vapour out the inlet, and that some of the water vapour will (due to gravitational effects), condense and collect at the bottom of the chamber, building up over time. Is this scenario achievable with CFX? If so, I haven't been able to discover how, as I've always needed to specify the volume fraction of the materials at the outlet, which is inherently the information I want to find out from the simulation. Thanks!

Your specification of the composition at the outlet is probably from reverse flow at an opening - it would need to be specified there. But for an outlet or an opening in forward flow it is unspecified and is convected from the cells in the domain - which is what you want.

You need to identify exactly what physics is going on here. Does the water condense on the walls or some other feature? Or does it condense in the air and fall as rain? Is anything else happening? Once you know the physics you have then you can look at models to simulate it.

condensation
 

Thanks for the reply. I know that some water vapour condenses on the walls but I do not know how much; this is one of the things I want to find out. That is, how much water vapour would collect in the chamber as a function of time. How do I go about specifying that water does condense on the walls, but that I do not know the amount?

Have a look at the wall condensation models. These are quite advanced multiphase models so you will probably need to get some help or examples from CFX support to get it working.