Pressure Gradient across leak

[hydrogen_joe]

Hi, thanks for reading

I am a grad who is working in hydrogen refueling systems. I am working on analysis on potential leaks at the moment as its key these are properly assessed and managed when working with hydrogen, for obvious reasons.

Our system is storing compressed hydrogen at 500 bar, from this I have estimated the mass flow rate of any leaks using the assumption of choked flow through the orifice. As per an equation similar to this:

https://www.engineersedge.com/pressure,045vessel/gas_discharge_rate_14170.htm

The ATEX standards require calculation of volumetric flow through the orifice by dividing through by hydrogen density. They seem to require that the atmospheric density of hydrogen is used rather than at 500bar? Does anyone know why we wouldn't use the density of the compressed hydrogen which 'is' leaking?

I assume there is some pressure distribution across the leaking area (thickness) from 500 - 1 bar but I can't understand why we are required to use the atmospheric density?

Thanks in advance
Joe

 

[LittleInch]

The equation gives you mass flow (lbs or kg per second). the choked mass flow equation includes the "real gas density" at upstream P & T so it is included there.

The ATEX want's to work out what the gas cloud is which is at atmospheric conditions. SO it wants volume of gas at atmospheric conditions.

Volume per second = mass per second divided by density

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