- #1
Elias Waranoi
- 45
- 2
Homework Statement
The pV-diagram in Fig. P20.51 (See attached file) shows the cycle for a refrigerator operating on 0.850 mol of H2. Assume that the gas can be treated as ideal. Process ab is isothermal. Find the coefficient of performance of this refrigerator.
Homework Equations
K = QC/|QH - QC|
pV = nRT
Cp = Cv + R
Isothermal expansion: Q = W = ∫p dV = nRT*ln(V2/V1)
Constant volume: Q = nCvΔT
Constant pressure: Q = nCpΔT
The Attempt at a Solution
QC = Qa-b + Qb-c = nRTa * ln(Vb/Va) + nCv(Tc - Tb) = paVa * ln(Vb/Va) + VbCv(pc - paVa/Vb)
QH = Qc-a = n(Cv + R)(Ta - Tc) = pc(Cv + R)(Va - Vc)/R
My answer K = QC/|QH - QC| = 0.462
Correct answer K = 6.23
What did I do wrong?