Yours is a fully CFD problem; about multiphase simulations, Comsol gives different physics as a choice:

Physics-> Add Physics -> Fluid Flow -> Multiphase Flow

there you find different methods, all based on what you want to simulate (bubbles, phase transport, fluid-structure interction etc.).

If you want to use Comsol, see examples on multiphase modeling (in fact, you have air and another gas, while the room walls I think are rigid walls). These are very good to get started.

However, from personal experience Your problem would be less computational consuming and difficult to implement in Ansys FLUENT (based on Finite Volume Method and specifically used to simulate fluids).

Best regards,

AP