Air that is not flowing in a closed system
 

Hi all,

I am working on 3d temperature distribution of some moulds.

There is a closed system that has only air not flowing there in moulds.

As the system is closed, density must be constant (mass and volume are constanst). Cp and thermal conductivity are defined as piece-polynomial. Thing I would like to ask is which state should be there? solid or fluid, as air is not flowing, I have defined it as ''SOLID'' . What should I do? Is there any thought?

If it's flowing it must be a fluid. Solids don't flow.

that is, I have done correct one ! :) Air should be defined as solid if it is in closed system, (1 wall, others are interface)