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Home ‣ Mechanical Engineering ‣ Heat Transfer, Refrigeration and Air Conditioning Comments
  • Question

  • A perfect black body is one which


  • Options
  • A. is black in colour
  • B. absorbs heat radiations of all wave lengths falling on it
  • C. reflects all the heat radiations
  • D. transmits the heat radiations

  • Correct Answer
  • absorbs heat radiations of all wave lengths falling on it 

    • Heat Transfer, Refrigeration and Air Conditioning problems

    Search Results

    • 1. A refrigeration system

    • Options
    • A. removes heat from a low temperature body and delivers it to a high temperature body
    • B. removes heat from a high temperature body and delivers it to a low temperature body
    • C. rejects energy to a low temperature body
    • D. none of the above
      • Discuss
    • 2. Thermal conductivity of water __________ with rise in temperature.

    • Options
    • A. remains same
    • B. decreases
    • C. increases
    • D. may increase or decrease depending upon temperature
      • Discuss
    • 3. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ? = Density of fluid, cp = Specific heat at constant pressure, and ? = Coefficient of absolute viscosity)

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 4. Thermal diffusivity is a

    • Options
    • A. function of temperature
    • B. physical property of a substance
    • C. dimensionless parameter
    • D. all of these
      • Discuss
    • 5. The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

    • Options
    • A. equal to one
    • B. greater than one
    • C. less than one
    • D. equal to Nusselt number
      • Discuss
    • 6. While designing the refrigeration system of an aircraft, the prime consideration is that the

    • Options
    • A. system has high C.O.P.
    • B. power per TR is low
    • C. mass of refrigerant circulated in the system is low
    • D. mass of the refrigeration equipment is low
      • Discuss
    • 7. The difference between dry bulb temperature and wet bulb temperature, is called

    • Options
    • A. dry bulb depression
    • B. wet bulb depression
    • C. dew point depression
    • D. degree of saturation
      • Discuss
    • 8. The wet bulb temperature lines, on the psychrometric chart, are curved lines.

    • Options
    • A. True
    • B. False
      • Discuss
    • 9. Nusselt number (NN) is given by

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 10. The relative humidity is defined as

    • Options
    • A. the mass of water vapour present in 1 m3 of dry air
    • B. the mass of water vapour present in 1 kg of dry air
    • C. the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.
    • D. the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure
      • Discuss

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