air flow to propane flow 1

[bandie]

I am looking at a relief valve with a relief pressure of 0.09 barg. The relief valve spec says that this corresponds to a flow of 10000 scm/hr of air.

What is the method for converting this flow of air to a flow of propane?

Is the volumetric flowrate effectively the same, with only the mass flow differing or is it more complicated than that?

Thanks

 

[Flareman]

One shorthand way to get an estimate of comparative flows through an orifice, at the same pressure, is to use the volumetric equivalent parameter

Veq = W (mass flow) * sqrt (Absolute Temp / Mol Wt)

as treat it as a constant when comparing flows at the same pressure. It's not perfect but at low pressures when the ratio of specific heats doesn't really come into play it should be close enough.

It also works fairly well for friction losses in piping as long as there's no significant difference in viscosity between the two compared fluids.

 

[jsummerfield]

Does the ASME Section VIII Appendix 10, Mandatory Conversions clarify this in a suitable manner?

John

 

[Flareman]

John
I think you mean Appendix 11, (at least in my copy).
Thanks, I didn't even know that was in there, I've been doing this from first principles all these years,
and.. it gives the more complete formula rather than my shorthand solution above.

 

[EGT01]

Bandie,

If you don't have a copy of ASME Section VIII, you can find the appropriate section as an excerpt in the Crosby Engineering Handbook.

http://www.andersongreenwood.com/literature.asp

Look near the bottom of the page for the link
Pressure Relief Valve Engineering Handbook CROMC-0296-US

 

[bandie]

That's great, thanks for your help.

 

[sailoday28]

What is the back pressure for the valve?

 

[bandie]

The back pressure varies between say 30 and 60 mbar.