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Units with use of the Ideal gas law?

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Old   April 8, 2009, 06:14
Default Units with use of the Ideal gas law?
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Michael
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Hi all

I have a little question about how CFX get the units to match when I use the setting Air Ideal gas. I have defined following expression in CFX-PRE:
\rho_{ref} = \frac{p_{ref} \cdot M_{air}}{R \cdot T}
whit the values of:
p_{ref}=1 atm
M_{air}=28.96 g/mol
T=293.65 K
and then I let CFX use the establish R in CFX and I get a density of the air in the unit kg/m^3. But I can not see how the units match, so could somebody give me a hint about how CFX get the units to match?

Thank you very much.

Kind regards
Michael
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Old   April 8, 2009, 07:11
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Lance
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R have units J K^-1 mol^-1 and simple dimensional analysis resolves your density to kg m^-3
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Old   April 8, 2009, 08:05
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Michael
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Quote:
Originally Posted by Lance View Post
R have units J K^-1 mol^-1 and simple dimensional analysis resolves your density to kg m^-3

Hi Lance

Thank you for your reply. I found out that I used a wrong value and unit for the gas constant but it gives the correct now.

Kind regards
Michael
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