Individual Gas Constant Units (lbm & lbf)
Individual Gas Constant Units (lbm & lbf)
(OP)
I was evaluating supersonic nozzle performance when I had a question about the units for the Gas Constant "R".
The Imperial units are:
[ft-lbf]/[lbm-°R]
What gave me a bit of trouble when balancing the choked mass flow equation is the relationship bewteen lbf and lbm.
(I typed the equation out in MS equation editor, but can't figure out how to put it here...)
Do you take these (lbm& lbf) as equivalent at STP conditions?
Thanks,
=stan
The Imperial units are:
[ft-lbf]/[lbm-°R]
What gave me a bit of trouble when balancing the choked mass flow equation is the relationship bewteen lbf and lbm.
(I typed the equation out in MS equation editor, but can't figure out how to put it here...)
Do you take these (lbm& lbf) as equivalent at STP conditions?
Thanks,
=stan
Beat to fit, paint to match.





RE: Individual Gas Constant Units (lbm & lbf)
For other uses you have to be really careful. I just calculated R for air in MathCad and got 53.355 (lbf*ft)/(lbm*R). If I just delete the lbf/lbm I get 1716.7 (ft^2/s^2*R). That looks like lbf/lbm is 1/g.
David
RE: Individual Gas Constant Units (lbm & lbf)
I want lbm/s and in the numerator is a lbf (from a psi number) that I'm not sure how to get into lbf.
Can I post a jpg directly into this text area? I'll post the equation I'm using.
Beat to fit, paint to match.
RE: Individual Gas Constant Units (lbm & lbf)
RE: Individual Gas Constant Units (lbm & lbf)
Beat to fit, paint to match.
RE: Individual Gas Constant Units (lbm & lbf)
This is not an answer to your specific question, but you might find it useful to look at the tabulation of a number of R values and their units to be found in this article on the online Citizendium:
http://en.citizendium.org/wiki/Molar_gas_constant
Milton Beychok
(Visit me at www.air-dispersion.com)
.
RE: Individual Gas Constant Units (lbm & lbf)
In Mathcad, psi ~ lbf/in^2
TTFN
FAQ731-376: Eng-Tips.com Forum Policies