[hotboy]

Hello friends!
When I read the user's guide of the fluent I wa confused by this:"Important:
For a closed domain, you can use the incompressible ideal gas law only with a fixed operating pressure. It cannot be used with a floating operating pressure. You can use the compressible ideal gas law with either floating or fixed operating pressure."


Rho=Pop/((R/Mw)xT) for Incompressible Ideal Gas flows.Pop and (R/Mw) are constants.When modeling the natural convection in closed domain ,the temperatur increase .It means that the density of gas is decrease as the temperature increase .It also meas that the total mass of the gas is decrease(the mass can't conserved)! It also means that we can't use incompressible ideal gas when modeling the natural convection in closed domain? The user's guide of fluent about this is wrong or my undestanding is wrong?

At last how can we set up the fluid density when modeling the natural convection in closed domain?ideal gas , incompressible ideal gas ,Polynomial?Thank you very much!

[hotboy]

I thougt this problem for a long time.Nobody give me any suggestion?