Refrigeration and Air-conditioning Miscellaneous


Refrigeration and Air-conditioning Miscellaneous

Refrigeration and Air-conditioning

  1. 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


  1. Clearance volume of a reciprocating compressor is 100 ml, and the volume of the cylinder at bottom dead centre is 1.0 litre. The clearance ratio of the compressor is









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    Clearance ratio =
    Clearance volume
    Swept volume

    =
    100
    =
    1
    1000 - 1009

    Correct Option: C

    Clearance ratio =
    Clearance volume
    Swept volume

    =
    100
    =
    1
    1000 - 1009



  1. A refrigerator uses R134a as its refrigerant and operates on a ideal vapour-compression refrigeration cycle between 0.14 MPa and 0.8 MPa. If the mass flow rate of the refrigerant is 0.05 kg/s, the rate of heat rejection to the environment is _______ kW.
    Given data:
    At P = 0.14 MPa, h = 236.04 kJ/kg , s = 0.9322 kJ/kgK
    At P = 0.8 MPa, h = 272.05 kJ/kg (superheated vapour)
    At P = 0.8 MPa, h = 93.42 kJ/kg (saturated liquid)









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    h1 = 236.04 kJ/kg
    h2 = 272.05 kJ/kg
    h3 = 93.42 kJ/kg
    s1 = 0.9322 kJ/kg
    ṁ = 0.05 kg/s
    Heat Rejection = ṁ(h2 – h3) = 0.05(272.05 – 93.42)
    Heat Rejection = 8.931 kW

    Correct Option: A


    h1 = 236.04 kJ/kg
    h2 = 272.05 kJ/kg
    h3 = 93.42 kJ/kg
    s1 = 0.9322 kJ/kg
    ṁ = 0.05 kg/s
    Heat Rejection = ṁ(h2 – h3) = 0.05(272.05 – 93.42)
    Heat Rejection = 8.931 kW


  1. List-I
    A. Liquid to suction heat exchange
    B. Constant volume heat addition
    C. Normal shock
    D. Ammonia-water
    List-II
    1. Vapour absorption refrigeration
    2. Vapour compression refrigeration
    3. Diesel cycle
    4. Otto cycle
    5. Converging nozzle
    6. Converging diverging nozzle









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    A – 2, B – 4, C – 6, D – 1

    Correct Option: A

    A – 2, B – 4, C – 6, D – 1



  1. 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 kW

    Correct Option: C

    Power required by compressor p = ṁ(h2 – h1)
    = 0.2 (276.45 – 237) = 7.9 kW