Heat Transfer Miscellaneous

Heat Transfer Miscellaneous

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Heat-Transfer

Heat Transfer Miscellaneous
  1. Grashof number signifies the ratio of








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    Grashof number = inertia force ×
    Buoyancy force
    (viscous force)2


    Correct Option: B

    Grashof number = inertia force ×
    Buoyancy force
    (viscous force)2


  1. The ratio of momentum diffusivity (υ) to thermal diffusivity (α), is called








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    Pr =
    μCp
    		 =
    ρVCp
    		 =
    V
    		 =
    V
    kkk / ρCpα

    Correct Option: A

    Pr =
    μCp
    		 =
    ρVCp
    		 =
    V
    		 =
    V
    kkk / ρCpα

  1. Match List-I with List-ll and select the correct answer using the code given below the lists:
    List-I List-II
    A. Grashof number 1. Mass diffusion
    B. Schmidt number 2. Transient heat conduction
    C. Weber number 3. Free convection
    D. Fourier number 4. Forced convection
    5. Surface tension
    6. Radiation









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    NA

    Correct Option: B

    NA

Direction: Heat is being transferred by convection from water at 48°C to a glass plate whose surface temp. is exposed to the water is at 40°C. The thermal conductivity of water is 0.6 W/mK and the thermal conductivity of glass is 1.2 W/mK. The spatial gradient of temperature in the water at the water-glass interface is dT/dy = 1 × 104 K/m.

  1. The heat transfer coefficient h in w/m2K is








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    For convection Heat flux, q = h(Tf – Ti)

    q = kw
    dT
    dyw

    = 0.6 × 1 × 104 = 6000 W/m
    ∴ h =
    q
    		 =
    6000
    		 = 750 W /m2K
    (Tf – Ti)8

    Correct Option: D

    For convection Heat flux, q = h(Tf – Ti)

    q = kw
    dT
    dyw

    = 0.6 × 1 × 104 = 6000 W/m
    ∴ h =
    q
    		 =
    6000
    		 = 750 W /m2K
    (Tf – Ti)8

  1. The value of the temperature gradient in the glass at the water-glass interface in K/m is








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    Temperature of water = 48° C
    Temperature of glass plate = 40° C
    Thermal conductivity of water = kw = 0.6 W/mK Thermal conductivity of glass = kG = 1.2 W/mK
    The spatial gradient of temperature in water at the water-glass interface

    =
    dT
    		 = 1 × 105 K/m
    dy


    At water glass interface
    q = kw
    dT
    		 = kG
    dT
    dywdyG

    ⇒
    dT
    		 =
    kw
    		 ×
    dT
    dyGkGdyw

    =
    0.6
    		 × 1 × 104 = 0.5 × 104 K/m
    1.1

    Correct Option: C

    Temperature of water = 48° C
    Temperature of glass plate = 40° C
    Thermal conductivity of water = kw = 0.6 W/mK Thermal conductivity of glass = kG = 1.2 W/mK
    The spatial gradient of temperature in water at the water-glass interface

    =
    dT
    		 = 1 × 105 K/m
    dy


    At water glass interface
    q = kw
    dT
    		 = kG
    dT
    dywdyG

    ⇒
    dT
    		 =
    kw
    		 ×
    dT
    dyGkGdyw

    =
    0.6
    		 × 1 × 104 = 0.5 × 104 K/m
    1.1