Gas Constant

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koehflow
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Joined: Thu Sep 27, 2012 8:24 pm

Gas Constant

Post by koehflow » Thu Sep 27, 2012 8:51 pm

In the gas discharge calculation the gas constant "R" is given as 53.34... lbft/lb degF. This is different then the typical R in psi cubic ft/Lbmole deg "R" How was the R in the calculation derived?

admin
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Joined: Mon Feb 08, 2010 7:47 pm

Re: Gas Constant

Post by admin » Thu Sep 27, 2012 8:59 pm

R in calculation is always transformed into SI unit from the unit that you use for input.
Actually all calculations are performed in SI units and results are shown in unit that you select.
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Babush1950
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Joined: Tue Feb 19, 2019 11:33 pm

Re: Gas Constant

Post by Babush1950 » Tue Feb 19, 2019 11:48 pm

I don't understand the gas constant R. In the formula PV=nRT.... R is a constant and does not change. It is different for SI vs US but it is a constant. What is your R constant. Apparently it is not constant since it changes based on the media and pressure and temp.

admin
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Re: Gas Constant

Post by admin » Wed Feb 20, 2019 8:21 pm

It is not changing with the pressure or the temperature. It is constant for a certain gas. R in terms of J/kg K is calculated as Ru/M where Ru is universal gas constant for any gas and particular molar mass. Ru = 8.314 J/mol K. In your formula pV=nRT you are using Ru. in a pV=mRT or p/rho = RT formula, it is R - gas constant for specific gas that it is used.
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