First slide
Thermodynamic processes
Question

A system undergoes three quasi-static processes sequentially as indicated in the given figure. 1-2 is an isobaric process, 2-3 is a polytropic process with γ = 4/3 and 3-1 is a process in which PV= constant. P2 = P1 = 4 x 105 N/m2, P3 =1 x 105 N/m2 and V1 = 1 m3.
The heat transfer for the cycle is ΔQ, the change in internal energy is ΔU and the work done is ΔW. Then

Moderate
Solution

For the process 31

P1V1=P3V3V3=P1V1P3=4×105×11×105=4m3

For the process 23

P2V2γ=P3V3γV2=P3P21γV3=41434=414m3=2m3

For the process 12,

W12=P1V2V1=(21)4×105J

For the process 23,

W23=P2V2P3V3(γ1)=(421×4)×105431=12(21)×105J

For the process 31,

W31=P1V1lnV3V1 =4×105×1×ln41ΔU=0

 ΔQ=ΔU+ΔW1231=4×105(21)+12×105(21)4×105×1.3861.08×105JΔQ=ΔW1.08×105J

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