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# "A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve".

## "A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve".

(OP)
I was wondering if anyone had the relevant excel spreadsheet regarding the below FAQ

FAQ1203-1293: A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve: A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve

I was having trouble calculating all the values. I can't seem to figure out how to calculate the flow rate, temperature, and density. I know it says PVT relationships are used, but I still have too many unknown variables. Any help is appreciated.

### RE: "A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve".

I've got it around here somewhere, but I'll guide you from memory. Temperature comes from an isentropic expansion from Po to Pn. That particular spreadsheet uses the ideal gas law, so rho = MWxP/RT. Flow rate = w = GnAn.

I think I posted an errata, but maybe not. I'm one off on the maximum G. When G decreased I should have backed up a step for the maximum. I didn't. Maybe I'll fix that one day, but for all practical purposes it's close enough.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

### RE: "A Simple Numerical Method for Gas/Vapor Flow in a Safety Valve".

suparida,
there are several threads discussing this topic at eng-tips,
see for example

which includes a Excel page to simulate the PSV as isentropic nozzle,
the method (based on rigorous API HEM procedure) is not too different from that described in FAQ and results are (usually) very close to the method included in library (analytical solution).

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