ChemCAD Heat Capacity Ratio Cp/Cv

Question

ChemCAD Heat Capacity Ratio Cp/Cv

hirschaplin (Petroleum)

(OP)

2 Mar 22 10:07

Hello,

I am working in a compressor selection software and I have to enter the heat capacity ratio (K-value or Cp/Cv value) of my inlet gas stream to proceed with the selection. How can I get the Cp/Cv value for my inlet gas stream in ChemCAD 7?

The molecular weight and Cp value is given in the stream report and easy to fill:

Thanks in advance.

pierreick (Chemical) · Answer 1 · 2022-03-02 11:28:28

Hi,
Consider Mayer's relation : Cp-Cv= R/Mw

Hope this is helping you
Pierre

hirschaplin (Petroleum) · Answer 2 · 2022-03-02 13:42:41

Hi Pierre,

Thanks for your feedback but that doesn't help me. I am out on deep water and I would like the program to give me the value without having to calculate myself since this is a bit outside my depth. Do you know if it is possible to get the program to give me the Cp/Cv value?

If I calculate R/Mw (8,314462618÷19,06) I get 0,4362 but I believe the correct Cp/Cv value should be between 1 and 1,7?

hirschaplin (Petroleum) · Answer 3 · 2022-03-02 14:00:34

I resolved it. There is an option in ChemCAD to control which properties the stream report shall show.

In the top menu, navigate to report -> quick view -> customize property set -> then select the properties you want to have in the report.

georgeverghese (Chemical) · Answer 4 · 2022-03-02 22:44:13

Better to use the average of the Cp/Cv between compressor inlet and outlet from Chemcad.

For ideal gases, Cp/Cv = k = Cp /(Cp-R), where Cp = kJ/kgmole/degK and R=8.314kJ/kgmole/degK. In many cases, the ideal gas value for k is far from the real gas k.

hirschaplin (Petroleum) · Answer 5 · 2022-03-03 10:32:56

Hi George,

In this case I have not modeled the compressor or outlet system yet. Only the inlet system.

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ChemCAD Heat Capacity Ratio Cp/Cv