TIme to vent a pressure vessel

[jgibbs22]

So a question has come up recently that I started working on, but was curious if anyone had done a generic calculation that estimates the time it would take to vent a pressure vessel filled with a ideal gas.

Basically, I am assuming the simple case where a valve is installed on a nozzle, and it is opened and the vessel allowed to vent. Looking to make a spreadsheet that will let you input the volume, valve diameter, and inital pressure, and then calculate the time it would take to vent to 20 psig. Anyone know of a resource that has done this already?

 

[racookpe1978]

If it is a big tank, the vent rate will be so low that cooling (due to expansion of the gas) will be very minor.

But, your inputs will be: initial pressure, final pressure, mass flow rate (will be proportional to pipe area (valve area * coef of flow, just like a pipe) but you need to account for the pipe length unless very, very short.)

 

[jgibbs22]

racookpe1978, thank you for the response.

The problem I run into is I am looking at 300 cubic foor tanks with nitrogen at 6000 psi, and if I open a valve on the end I want to know how long it would take to vent down to 10 psig. You can't just put in 6,000 and 10, as the density is constantly changing, so the flow rate will continually decrease. I know form expereience it could take 4-5 hours to vent a 4400 psi tank at about 200 cubic feet close to zero, but am having trouble forming the analysis to prove it.