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Mechanical Engineering Objective Questions { Heat Transfer }

57. Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in
A.Electric heater
C.Steam Condenser
D.Refrigerator condenser coils

58. According to Prevost theory of heat exchange
A.It is impossible to transfer heat from low temperature source to high temperature source
B.Heat transfer by radiation requires no medium
C.All bodies above absolute zero emit radiation
D.Heat transfer in most of the cases takes place by combination of conduction, convection and radiation

59. When heat is transferred by molecular collision, it is referred to as heat transfer by

60. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as K1 = 2K2 will be

61. Sensible heat is the heat required to
A.Change vapor into liquid
B.Change liquid into vapor
C.Increase the temperature of a liquid of vapor
D.Convert water into steam and superheat it

62. A grey body is one whose absorptivity
A.Varies with temperature
B.Varies with wavelength of the incident ray
C.Is equal to its emissivity
D.Does not vary with temperature and wavelength of the incident ray

63. Thermal diffusivity is
A.A dimensionless parameter
B.Function of temperature
C.Used as mathematical model
D.A physical property of the material

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