72. Log mean temperature difference in case of counter flow compared to parallel flow will be
(a) same
(b) more
(c) less
(d) depends on other factors
(e) none of the above.
Ans: b
73. The energy distribution of an ideal reflector at higher temperatures is largely in the range of
(a) shorter wavelength
(b) longer wavelength
(c) remains same at all wavelengths
(d) wavelength has nothing to do with it
(e) none of the above.
Ans: a
74. Total emissivity of polished silver compared to black body is
(a) same
(b) higher
(c) more or less same
(d) very much lower
(e) very much higher.
Ans: d
75. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
(a) absolute temperature
(b) square of temperature
(c) fourth power of absolute temperature
(d) fourth power of temperature
(e) cube of absolute temperature.
Ans: c
76. Which of the following property of air does not increase with rise in temperature
(a) thermal conductivity
(b) thermal diffusivity
(c) density
(d) dynamic viscosity
(e) kuiematic viscosity.
Ans: c
77. The unit of Stefan Boltzmann constant is
(a) watt/cm2 °K
(b) watt/cm4 °K
(c) watt2/cm °K4
(d) watt/cm2 °K4
(e) watt/cm2 °K2.
Ans: d
78. In free con-vection heat transfer, Nusselt number is function of
(a) Grashoff no. and Reynold no.
(b) Grashoff no. and Prandtl no.
(c) Prandtl no. and Reynold no.
(d) Grashoff no., Prandtl no. and Reynold no.
(e) none of the above.
Ans: b
79. Stefan Boltzmann law is applicable for heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) conduction and radiation combined
(e) convection and radiation combined.
Ans: c
80. 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
(e) same as for the liquids.
Ans: a
(a) same
(b) more
(c) less
(d) depends on other factors
(e) none of the above.
Ans: b
73. The energy distribution of an ideal reflector at higher temperatures is largely in the range of
(a) shorter wavelength
(b) longer wavelength
(c) remains same at all wavelengths
(d) wavelength has nothing to do with it
(e) none of the above.
Ans: a
74. Total emissivity of polished silver compared to black body is
(a) same
(b) higher
(c) more or less same
(d) very much lower
(e) very much higher.
Ans: d
75. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
(a) absolute temperature
(b) square of temperature
(c) fourth power of absolute temperature
(d) fourth power of temperature
(e) cube of absolute temperature.
Ans: c
76. Which of the following property of air does not increase with rise in temperature
(a) thermal conductivity
(b) thermal diffusivity
(c) density
(d) dynamic viscosity
(e) kuiematic viscosity.
Ans: c
77. The unit of Stefan Boltzmann constant is
(a) watt/cm2 °K
(b) watt/cm4 °K
(c) watt2/cm °K4
(d) watt/cm2 °K4
(e) watt/cm2 °K2.
Ans: d
78. In free con-vection heat transfer, Nusselt number is function of
(a) Grashoff no. and Reynold no.
(b) Grashoff no. and Prandtl no.
(c) Prandtl no. and Reynold no.
(d) Grashoff no., Prandtl no. and Reynold no.
(e) none of the above.
Ans: b
79. Stefan Boltzmann law is applicable for heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) conduction and radiation combined
(e) convection and radiation combined.
Ans: c
80. 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
(e) same as for the liquids.
Ans: a
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