How to modify gas constant or special heat ratio in CFX-Pre?

compressor · August 24, 2017, 00:58

I must modify gas constant or specific heat ratio in CFX-Pre.
Because I investigate the effect of fuild property, such as operating characteristics when the gas constant is constant and specific heat ratio is different.
Thanks

Jiricbeng · August 24, 2017, 05:33

If you modify molar mass M, you also modify specific gas constant r (r=R/M), so you modify also heat ratio Cp/Cv. See Mayer's relation for gas (Cp = Cv + r).

compressor · August 24, 2017, 06:49

Could I modify directly gas constant or specific heat ratio in CFX-Pre?

Opaque · August 24, 2017, 09:22

You cannot modify the specific heat ratio, nor the gas constant directly in CFX-Pre.

May I ask what is your goal changing the gas constant, and/or the specific heat ratio? It seems you are making an assumption those quantities are used inside the software somehow. From what I understand, they are not used anywhere explicitly.

You can rewrite the fundamentals in reverse

R_gas = R_universal / Molar Mass ---> Molar Mass = R_universal / R_gas which you can change at will

Cp - Cv = R_gas
Cv = Cp / SpecificRatio --> Cp = SpecificRatio * R_gas / (SpecificRatio - 1)

Hope the above helps,

August 24, 2017, 00:58	How to modify gas constant or special heat ratio in CFX-Pre?	#1
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 8	I must modify gas constant or specific heat ratio in CFX-Pre. Because I investigate the effect of fuild property, such as operating characteristics when the gas constant is constant and specific heat ratio is different. Thanks

August 24, 2017, 06:49	Could I modify directly gas constant or specific heat ratio in CFX-Pre?	#3
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 8	Could I modify directly gas constant or specific heat ratio in CFX-Pre?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Setting the height of the stream in the free channel	kevinmccartin	CFX	12	October 13, 2022 21:43
Thermally coupling 1D gas flow to 3D heat conduction in solid	Pyotr	CFX	5	March 6, 2017 21:46
Multiphase flow - incorrect velocity on inlet	Mike_Tom	CFX	6	September 29, 2016 01:27
Convective heat transfer issues in CFX	techtuner	CFX	30	May 14, 2016 09:55
convergenceof natural convection prob. in cfx	cpkewat	CFX	15	January 31, 2014 06:29

August 24, 2017, 05:33		#2
Jiricbeng Senior Member Jiri Join Date: Mar 2014 Posts: 218 Rep Power: 13	If you modify molar mass M, you also modify specific gas constant r (r=R/M), so you modify also heat ratio Cp/Cv. See Mayer's relation for gas (Cp = Cv + r).

August 24, 2017, 09:22		#4
Opaque Senior Member Join Date: Jun 2009 Posts: 1,804 Rep Power: 32	You cannot modify the specific heat ratio, nor the gas constant directly in CFX-Pre. May I ask what is your goal changing the gas constant, and/or the specific heat ratio? It seems you are making an assumption those quantities are used inside the software somehow. From what I understand, they are not used anywhere explicitly. You can rewrite the fundamentals in reverse R_gas = R_universal / Molar Mass ---> Molar Mass = R_universal / R_gas which you can change at will Cp - Cv = R_gas Cv = Cp / SpecificRatio --> Cp = SpecificRatio * R_gas / (SpecificRatio - 1) Hope the above helps,