Pressure Outlet
 

Hi! I have a question on using Pressure outlet as a boundary condition.

My model involves a closed-end room( one end is open, the other is closed). It behaves like a close-end pipe.

My question is, by setting the open end as pressure outlet, would there be any air mass flow in/out through this open end. This is because the room is subjected to temperature changes, and the internal air within the room experiences temperature variances.

And if so, is this condition regarded as a ventilated room?

Thanks!

Hi Jonathan,

A pressure outlet works both as inlet and outlet - you set the pressure on the outside of the boundary, and based on the pressure difference flow will occur. If the inside pressure is lower, flow will be inward (you will see a "reversed flow in ... faces" notification)

Although I have no experience with modelling free convection in rooms, I'd say it's a suitable boundary condition.

Cheers,
Cees

hi Cees,

oh wow! thanks for the clarification! one more question though. if the inner pressure is higher, this will cause an outflow of air. however, without any inflow of air on the other side, wouldn't the mass equilibrium not being fulfilled?

Thanks,
Jonathan

Just wanted to point out, steady flow mass balance applies only to equilibria (i.e. steady state). In transient problems you can have mass flow in an open-ended pipe (like the emptying of a tank). Is your problem stationary or transient?

For steady state case, there would have to be reverse flow to satisfy mass conservation (steady flow mass balance). For transient, there is no such condition (because the flow is not necessarily steady).