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Thermodynamics: Efficiency for Stirling engine 
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#1
Nov1611, 09:18 PM

P: 196

1. The problem statement, all variables and given/known data
I'm trying to find an expression for the efficiency of a stirling engine operating with an ideal diatomic gas, and cycling through a volume V and a multiple of its compression ratio, r, Vr. 2. Relevant equations processes: 12 isothermal expansion 23 isochoric cooling 34 isothermal compression 41 isochoric heating r=compression ratio Th=high temperature Tl=low temperature Work=W1 proc. 12 (nRTh)ln(r) Work=W2 proc. 34 (nRTl)ln(1/r) Work Net= W1W2= nRln(r)(ThTl) since ln=ln(1/r) Heat Input=Qh=nCv(ThTl)=(5/2)R(ThTl) Efficiency=e=W Net/Heat Input=[nRln(r)(ThTl)]/[(5/2)nR(ThTl) Canceling:e=(5/2)ln(r) This does not Make sense since efficiency for an engine with an equal compression ration of say r=10 operating at a Temp high of 300k and low of 200k would have a carnot efficiency of (1/3) while with the above equation e=.92 which is impossible. 


#2
Nov1611, 10:04 PM

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#3
Nov1711, 12:51 AM

P: 196

Yes, but the heat flow occurring in 23 is an out flow so it wouldn't be included in the efficiency calculation which is based on only on the heat input, right?



#4
Nov1711, 03:05 AM

P: 374

Thermodynamics: Efficiency for Stirling engine
I believe Qh=5/2*R*n*(ThTl)+R*n*Th*ln(r) in the denominator



#5
Nov1711, 03:29 AM

P: 196

why is that? isn't nRThln(r) the work done from 12?



#6
Nov1711, 03:51 AM

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#7
Nov1711, 11:48 AM

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#8
Nov1711, 11:52 AM

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