Polytropic
Hi again, just wondering about this:
"Air is compressed in a reversible polytrophic process (pv^n=constant) from an initial state of 15 bar and
100 ° to a final pressure of 50 bar. The polytropic exponent is n=1.3. Calculate the change in
entropy per mass of air."
Would we use perfect gas relationships - specific - pv=RT at state 1. Looking at entropy in tables though, they show a change in entropy. Not sure about this one.
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Sorry for not explaining where that formula came from.
There are 3 standard relationships for calculation of entropy of ideal gases when specific heat is constant.
3 relations being
1. When you know temp and volume
2. When you know temp and pressure
3. When you know pressure and volume of initial and final states.
Also, the one I used for temperature T2 can be easily derived. Pv^n = C relation by replacing terms for temp.