Refrigeration and Air-conditioning Miscellaneous
- Refrigerant vapor enters into the compressor of a standard vapor compression cycle at –10°C (h = 402 J/kg) and leaves the compression at 50°C (h = 432 kJ/kg). It leaves the condenser at 30°C (h = 237 kJ/kg). The COP of the cycle is ________.
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Work done = 432 – 402 = 30 kJ/kg
Refrigerating effect = 402 – 237 = 165 kJ/kg.COP = 165 = 5.5 30 Correct Option: B
Work done = 432 – 402 = 30 kJ/kg
Refrigerating effect = 402 – 237 = 165 kJ/kg.COP = 165 = 5.5 30
- The power required for compressor in kW is
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Power required by compressor p = ṁ(h2 – h1)
= 0.2 (276.45 – 237) = 7.9 kWCorrect Option: C
Power required by compressor p = ṁ(h2 – h1)
= 0.2 (276.45 – 237) = 7.9 kW
- The rate at which heat is extracted, in kJ/s from the refrigerated space is
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Rate at which heat is extracted = ṁ(h1 – h4)
= 0.2 (237 – 95.5) = 28.3 kWCorrect Option: A
Rate at which heat is extracted = ṁ(h1 – h4)
= 0.2 (237 – 95.5) = 28.3 kW
- In an ideal vapour compression refrigeration cycle, the specific enthalpy of refrigerant (in kJ/kg) at the following states is given as :
Inlet of condenser : 283
Exit of condenser : 116
Exit of evaporator : 232
The COP of this cycle is
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1– 2 → work done by the compressor
2 – 3 → condenser heat rejected at constant pressure
3 – 4 → throttling
4 – 1 → heat addition in evaporator
Given: h2 = 283 kJ/ kg
h3 = 116 kJ/kg = h4 (from ph curve)
h1 = 232 kJ/kg
We knowC.O.P = desired effect = Cooling effect work input work done by compressor C.O.P = h1 – h4 = 232 - 116 = 2.27 h2 – h1 283 - 232
Correct Option: A
1– 2 → work done by the compressor
2 – 3 → condenser heat rejected at constant pressure
3 – 4 → throttling
4 – 1 → heat addition in evaporator
Given: h2 = 283 kJ/ kg
h3 = 116 kJ/kg = h4 (from ph curve)
h1 = 232 kJ/kg
We knowC.O.P = desired effect = Cooling effect work input work done by compressor C.O.P = h1 – h4 = 232 - 116 = 2.27 h2 – h1 283 - 232
- The vapour compression refrigeration cycle is represented as shown in the figure below, with state 1 being the exit of the evaporator. The coordinate system used in this figure is
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T-h curve
Correct Option: D
T-h curve