[cloudnqh]

I'm doing a natural convection modeling for the flow and radiation inside a container. The air pressure inside the container is very low, e.g. 30 tor. It seems that I can not use the boussinesq model because beta*(T-T0)=5>1. What should I use to model the natural convection?

I have two thoughts which need your help:
(1) Define density as a function of temperature?
If I define the density as a function of temperature, how to define the operating pressure and operating density? What I did is to set the operating pressure as 30 tor and set the operating density of the air under 30 tor. Also I calculated the density under 30 tor and different temperatures. But I got divergency error. Please tell me if this method is not good.

Or (2) choose the imcompressible ideal gas model?
The operating pressure is very low and container internal hot surface temperature Th is very high, does that mean I can use the imcompressible ideal gas model?

Thanks a lot for your help!

Eric