# Isentropic Specific Enthalpy HELP

1. Aug 23, 2011

### bobboviking

Hi guys,

I'm struggling with some equations regarding the enthalpy change over a compressor in a vcc system.

I'm currently working on a model for the whole system and I think I've got all equations except the one describing the enthalpy difference betweeen the inlet and outlet of the compressor.
I can't really understand how to handle the isentropic specific enthalpy, hout,s, in the following equation:

hout = (hout,s - hin)/ns + hin

where ns is the isentropic efficiency

I also know that ns = (Tout,s-Tin)/(Tout-Tin) (assuming constant specific heat)

I would prefer the model to be as "general" as possible, meaning that I don't have to perform a bunch of experimental test to determine certain coefficients.

I would greatly appreciate some help with how to calculate/estimate hout,s. I think that the value of hout,s depends on the suction pressure (?) so assuming a constant value (from example a table at some operating condition) isn't good enough for an accurate model? I mean that value of hout,s does change when the system moves from that particular condition, right?