I am modelling the flow inside a chemical reactor for coal gasification.There is the mixture of coal particle and air in one inlet and plasma flow ,which should be in some sense another phase,in the other radicl inlet.I use two phase flow model for the coal and air,but I don't know what should I treat the plasma.Should I treat it as a scalar? And I am currently not very clear that why one kind of gas is treat as a scalar in STAR-CD instead of using another material when two different kinds of gas are flowing together. Your suggestion will be greatly appreciated!

I can't answer your entire question, but I can explain a little. When STAR says different materials, it really means different fluid streams. For example, in a car radiator, one material (fluid stream) is the air, and another fluid stream is the coolant. They never touch, but simply transmit heat through a conductive solid barrier.

Within air, you could treat it as several gases (ie oxygen, nitrogen, ...) each one defined as scalar and having separate properties. The key is that they all exist together in the same fluid stream. If you had a room starting with 100% nitrogen, and then started injecting oxygen, you could track the progress of the oxygen plume for example by defining it as a separate scalar.

so how to model two fluid stream mixing together?

Call user support and ask.

Aaron, If two streams actually mix, they are considered as one stream within the contect of STAR-CD. There is a dilution pipe example in the STAR-CD tutorials manual that shows this. There is are two inlets each with a different constituent make up. They then mix.

Now if the two fluids are different phases... Thats a eularian two phase problem and the set up is more complex but it is still on fluid stream.

- Andy