cfx-pre

compressor · August 23, 2017, 10:11

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

compressor · August 23, 2017, 10:18

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

Opaque · August 23, 2017, 11:12

Why would you do that?

The gas constant should never be modified. It is the universal constant divided by the molar mass. Therefore, the knob to change is the molar mass

The specific ratio is Cp/Cv, and Cv = Cp + R; therefore, nothing to change.

It is bad practice to change dependent quantities. It usually ends up with some thermodynamic inconsistency downstream.

I would think twice before changing such quantities.

compressor · August 24, 2017, 00:21

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

compressor · August 24, 2017, 00:22

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

Opaque · August 24, 2017, 09:25

The gas constant is not a fundamental thermodynamic parameter, neither is the specific ratio.

If you are modifying such parameters, you are effectively modifying the molar mass (different material or composition), and one of the specific heat variables.

compressor · August 25, 2017, 07:55

You means that I should modify gas constant or specific heat ratio by changing molar mass or specific heat capcity(constant pressure) in CFX-Pr?

August 23, 2017, 10:11	cfx-pre	#1
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 9	How to modify gas constant or special heat ratio in CFX-Pre?

August 23, 2017, 10:18	How to modify gas constant or special heat ratio in CFX-Pre?	#2
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 9	How to modify gas constant or special heat ratio in CFX-Pre? Thanks

August 24, 2017, 00:21	I must modify gas constant or specific heat ratio	#4
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 9	I must modify gas constant or specific heat ratio.Because I investigate the effect of fuild property, such as operating characteristics when the gas constant is constant and specific heat ratio is different.

August 25, 2017, 07:55	How to modify gas constant or specific heat ratioinCFXPre?	#7
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 9	You means that I should modify gas constant or specific heat ratio by changing molar mass or specific heat capcity(constant pressure) in CFX-Pr?

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August 23, 2017, 11:12		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,862 Rep Power: 33	Why would you do that? The gas constant should never be modified. It is the universal constant divided by the molar mass. Therefore, the knob to change is the molar mass The specific ratio is Cp/Cv, and Cv = Cp + R; therefore, nothing to change. It is bad practice to change dependent quantities. It usually ends up with some thermodynamic inconsistency downstream. I would think twice before changing such quantities.

August 24, 2017, 00:22		#5
compressor New Member xuhaoyang Join Date: Aug 2017 Posts: 7 Rep Power: 9	I must modify gas constant or specific heat ratio.Because I investigate the effect of fuild property, such as operating characteristics when the gas constant is constant and specific heat ratio is different.

August 24, 2017, 09:25		#6
Opaque Senior Member Join Date: Jun 2009 Posts: 1,862 Rep Power: 33	The gas constant is not a fundamental thermodynamic parameter, neither is the specific ratio. If you are modifying such parameters, you are effectively modifying the molar mass (different material or composition), and one of the specific heat variables.