Heat Transfer

41. Heat transfer takes place as per -

  1. zeroth law of thermodynamics
  2. first law of thermodynamic
  3. second law of the thermodynamics
  4. Kirchoff's law (e) Stefan's law.
  5. none

Correct answer: (C)
second law of the thermodynamics

42. hermal diffusivity of a substance is

  1. directly proportional to thermal conductivity
  2. inversely proportional to density of substance
  3. inversely proportional to specific heat
  4. all of the above
  5. none of the above.

Correct answer: (D)
all of the above

43. hich of the following property of air does not increase with rise in temperature

  1. thermal conductivity
  2. thermal diffusivity
  3. density
  4. dynamic viscosity
  5. kuiematic viscosity.

Correct answer: (C)
density

44. If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of

  1. 3
  2. 6
  3. 9
  4. 27
  5. 81

Correct answer: (E)
81

45. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

  1. convection
  2. radiation
  3. conduction
  4. both convection and conduction
  5. none of the above.

Correct answer: (C)
conduction

46. In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by

  1. hr (time)
  2. sqm (area)
  3. °C (temperature)
  4. cm (thickness)
  5. kcal (heat).

Correct answer: (D)
cm (thickness)

47. ll radiations in a black body are

  1. reflected
  2. refracted
  3. transmitted
  4. absorbed
  5. partly reflected and partly absorbed.

Correct answer: (D)
absorbed

48. Metals are good conductors of heat because

  1. their atoms collide frequently
  2. their atoms-are relatively far apart
  3. they contain free electrons
  4. they have high density
  5. all of the above.

Correct answer: (A)
their atoms collide frequently

49. Moisture would find its way into insulation by vapour pressure unless it is prevented by

  1. high thickness of insulation
  2. high vapour pressure
  3. less thermal conductivity insulator
  4. a vapour seal
  5. all of the above.

Correct answer: (D)
a vapour seal

50. MTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is

  1. higher
  2. lower
  3. same
  4. depends on the area of heat exchanger
  5. depends on temperature conditions.

Correct answer: (A)
higher

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