Gas flow from one chamber to another

1. Jul 15, 2013

geologic

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

2. Jul 15, 2013

SteamKing

Staff Emeritus
You will also need to know the details of the connection between the two chambers (i.e., the internal diameter, the length, any fittings like valves, etc.) You will also need to determine if the flow will be isothermal or adiabatic.

3. Jul 15, 2013

geologic

Ok, so lets say I know the details of the valves, tubes, etc.

I'm not sure if the flow is adiabatic (I'm not putting in any heat, the experiment is done at room temperature). If there is cooling/heating upon expansion, then heat could transfer in through the metal chamber. Any ideas how I can ensure that the flow is one or the other? It isn't possible to thermally isolate the system I'm using. How can I estimate how important these effects are?

4. Jul 15, 2013

SteamKing

Staff Emeritus
To make the process adiabatic (or reasonably so), wrap your chambers in insulating material, if this is practical. Another line of reasoning would be to assume that if the entire process occurs in a short amount of time, no significant quantity of heat could have entered or exited the chambers in that brief period.

5. Jul 15, 2013