Gas flow from one chamber to another

Hi,

I don't know a ton of fluid mechanics, and haven't been able to mathematically define this problem, so I was hoping someone might have an idea.

The problem I want to solve is the time it takes for gas to flow from one chamber (with finite pressure) to another (vacuum). The problem is non-equilibrium and fluid velocity is time-dependent (when the pressures are almost equal, the fluid flow should be slow (I would think)). So the known quantities would be the initial pressures, volumes and temperature and I want to calculate the time to equilibrium (or, effectively, the time-constant).

Thanks,
geo