A mass of 2 kg of air in a vessel expands from 3 bar, 70c to 1 bar, 40, while receiving 1.2 kj of heat from a reservoir at 120. the environment is at 0.98 bar, 27c. calculate the maximum work and the work done on the atmosphere.
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A mass of 2 kg of air in a vessel expands from 3 bar, 70c to 1 bar, 40, while receiving 1.2 kj of heat from a reservoir at 120. the environment is at 0.98 bar, 27c. calculate the maximum work and the work done on the atmosphere.
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Answer:
Maximum work from gas
= u1 – u2 – To ( s1-s2)
= m Cv( T1-T2)-To((mCpln(T1/T2) -mRln(P1/P2)]
= m[Cv( T1-T2)-To((Cpln(T1/T2) -Rln(P1/P2)]
= 2[0.718(343-313)-300[ 1.005ln(343/313) -.287ln(3/1)]
= 177.07 kJ
Work done on the atmosphere = p0 (V2 – V1)
= 98[mR(T2/P1) -mR(T1/P1)]
= 111.75 kJ
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