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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Hi,
dS can be directly calculated from equation,
ds = Cp*ln(T2/T1) - R*ln(P2/P1)
Cp = 1.005 kJ/kg.K
R = 0.287 kJ/kg.K
T2 can be calculated using the relation
T2/T1 = (P2/P1)^((n-1)/n)
I got,
T2= 492.46 K and dS = -0.0663 kJ/kgK