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Mechanical Engineering Objective Questions { Heat Transfer }

64. The thermal diffusivities for gases are generally
A.More than those for liquids
B.Less than those for liquids
C.More than those for solids
D.Dependent on the viscosity

65. Thermal diffusivity of a substance is
A.Proportional of thermal conductivity (k)
B.Inversely proportional to (k)2
C.Proportional to (k)2
D.None of the above

66. Thermal conductivity of wood depends on
D.All of the above

67. Heat conducted through unit area and unit thick face per unit time when temperature difference between opposite faces is unity, is called
A.Thermal resistance
B.Thermal coefficient
C.Temperature gradient
D.Thermal conductivity

68. Emissivity of a white polished body in comparison to a black body is
D.Depends upon the shape of body

69. A non-dimensional number generally associated with natural convection heat transfer is
A.Grashof number
B.Nusselt number
C.Weber number
D.Prandtl number

70. Fourier's law of heat conduction is valid for
A.One dimensional cases only
B.Two dimensional cases only
C.Three dimensional cases only
D.Regular surfaces having non-uniform temperature gradients

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