How do i calculate i leak flow rate?

[scott1205]

We have a vessel which I know the physical volume of. We pressurise the vessel up to a fixed pressure. (Normally around 7bar and is measured with a monometer) We then seal the vessel off for a fixed amount of time (5 mins) we then take the reading from the monometer again. From this we have the pressure drop in that time. What I am trying to work out is what the leak rate will be from these two readings.(CC/M if possible) How can this be done?

Thanks
Scott

 

[FreddieH]

This may help

http://www.prosensys.com/pdfs/leak-rate_calculation.pdf

 

[fegenbush]

What are the approximate dimensions of the vessel? With what are you pressurizing it?

 

[scott1205]

The vessel in this instance is small, only 0.45m3 and we are just using compressed air. However I would like to know the process of how this would be worked out so this could be repeated for all of our product range.

Thanks
Scott

 

[scott1205]

http://www.prosensys.com/pdfs/leak-rate_calculatio...

wont work for me because i dont know the leak area. I just know the pressure drop.

 

[LittleInch]

In relatively simple terms, calculate the mass of air at the start by Vol X density of air at 1 bara x pressure in bara (8 in your case). Then subtract the mass left after 5 minutes by the same calcualtion but with your redeuced pressure. Providing the pressure fall isn't significant (less than 1 bar), then this should give you the mass of air/ minute leaking out.

As this will be choked flow, substitute this into a choked flow orifice calcualtion (many available) to get your voumetric flow rate or area of hole or simply divide your mass flow rate by density at atmospheric to get standard volumetric flow rate of air.

This won't be exact as air isn't a perfect gas and needs your test air to be close to 15 Deg C, but this should get you close to what you need. This looks too simple so I will stand to be corrected....

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way