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Cp/cv Ratio


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#1 DANA-IF

DANA-IF

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Posted 10 March 2014 - 04:20 AM

Hi friends :)

 

I'd like to ask why the ratio cp/cv isn't constant between suction and discharge in a compressor in many cases

 

Thanks a lot 



#2 ankur2061

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Posted 10 March 2014 - 04:28 AM

N.BH,

 

Because the pressure / temperature conditions at suction and discharge are not the same. This is specifically true when the compression ratio (Pd / Ps) is very high for a given compression process.

 

Regards,

Ankur.



#3 DANA-IF

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Posted 10 March 2014 - 04:38 AM

Thanks ,  I have also another question for a case when Cp/Cv  is constant  for suction and discharge stream :

 

 

In the GPSA BOOK it's indicated that the isentropic exponent is the ratio Cp/Cv 

 

but when I look into HYSYS , I find that they don't have the same value 

 

For example : Cp/Cv = 1.263 for suction and discharge stream 

 

                               isentropic exponent =1.1708


Edited by N.BH, 10 March 2014 - 04:40 AM.


#4 ankur2061

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Posted 10 March 2014 - 04:54 AM

N.BH,

 

The term isentropic exponent is used for real gases whereas writing just Cp/Cv denotes ideal gas conditions. The wikipedia link below distinguishes this as gamma (γ) for ideal gas and kappa (κ) for real gas:

 

http://en.wikipedia...._capacity_ratio

 

Regards,

Ankur






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