Question

11 - The following data is given for an ideal vapor-compression refrigeration cycle: At the inlet of the compressor h=250 kJ/kg At the exit of the condenser h=400 kJ/kg At the inlet of the evaporator h=75 kJ/kg If the compressor had an isentropic efficiency of 80 %, the heat rejected (kJ/kg) from the cycle would be.... (assume that enthalpies do not change, except the one at the exit of the compressor) a) 363 b) 325 188 d) 295 e) 175

Answer 1

• In an ideal vapour compression refrigeration cycle process 3-4 iso-enthalpic process.
• In this problem two conditions are given for processe 3-4. One at the exit of condenser (i.e. h₃) and one at inlet of evaporator( i.e h₄)
• According to standard Vapour compression refrigeration cycle h₃=h₄ and h₂>h1>h₃
• But h₃>h₁ given in problem which is wrong. Taking enthalpy at inlet of condenser as h₂=400 kJ/kg
  Criven) Ideal Vapour compression Refrigeration Gale hi= 250 KI 1 kg ha = 400 kJ 1 kq ha = hq = 75 kilke Visentropic 80% 1 P T a QR 1h=c Win. SECT S=0 PA 4 S fig he ha P-h diagram (ideal VCR) fig. Tos diagram 1-2-3-4 - ideal Process 1-2-3-4 Actual Process = 400-250 h2²- 250 Nisenhopic ha hi 0.80 hathi ha = 400-250 250 = 437.5 kol kg QR Cheat Rejected from chole) - hal- ha 3 437.5-75 PR-362.5 ~ 363 KJ Ike 4 Ans