Refrigeration and Air-conditioning Miscellaneous


Refrigeration and Air-conditioning Miscellaneous

Refrigeration and Air-conditioning

  1. A vapour absorption refrigeration system is a heat pump with three thermal reservoirs as shown in the figure. A refrigeration effect of 100 W is required at 250 K when the heat source available is at 400 K. Heat rejection occurs at 300 K. The minimum value of heat









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    From question, since refrigeration effect of 100 W is required

    So,
    100
    =
    250
    Work obtained300 – 250

    Work obtained = =
    100 × 50
    = 20 W
    250


    Now for this amount of work, heat is absorbed from reservoir 3 and rejected to sink 2.
    ∴ η =
    W
    = 1 -
    300
    =
    1
    Q34004

    ⇒ Q3 = 4W = 4 × 20 W = 80 W

    Correct Option: C

    From question, since refrigeration effect of 100 W is required

    So,
    100
    =
    250
    Work obtained300 – 250

    Work obtained = =
    100 × 50
    = 20 W
    250


    Now for this amount of work, heat is absorbed from reservoir 3 and rejected to sink 2.
    ∴ η =
    W
    = 1 -
    300
    =
    1
    Q34004

    ⇒ Q3 = 4W = 4 × 20 W = 80 W


  1. An industrial heat pump operates between the temperatures of 27°C and -13°C. The rates of heat addition and heat rejection are 750 W and 1000 W, respectively. The COP for the heat pump is









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    Heat addition, Q2 = 750 W
    Heat rejected, Q1 = 1000 W

    [C.O.P]H.P =
    Q1
    =
    Q1
    WQ1 - Q2

    =
    1000
    =
    1000
    = 4
    1000 - 750250

    T1 = 273 + 27º = 300ºK

    T2 = 273 – 13 = 260K
    [C.O.P]H.P =
    Q1
    Q1 - Q2

    for actual heat pump
    =
    1000
    =
    1000
    = 4
    1000 - 750250

    Correct Option: C

    Heat addition, Q2 = 750 W
    Heat rejected, Q1 = 1000 W

    [C.O.P]H.P =
    Q1
    =
    Q1
    WQ1 - Q2

    =
    1000
    =
    1000
    = 4
    1000 - 750250

    T1 = 273 + 27º = 300ºK

    T2 = 273 – 13 = 260K
    [C.O.P]H.P =
    Q1
    Q1 - Q2

    for actual heat pump
    =
    1000
    =
    1000
    = 4
    1000 - 750250



  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. 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