Mechanical Engineering MCQs

Page No. 151

Thermal diffusivity of a substance is __________________?


adirectly proportional to thermal con¬ductivity


binversely proportional to density of substance


cinversely proportional to specific heat


dall of the above


View Answer all of the above

Stefan Boltzmann law is applicable for heat transfer by __________________?


aconduction


bconvection


cradiation


dconduction and radiation combined


View Answer radiation

The unit of Stefan Boltzmann constant is ____________________?


awatt/cm2 °K


bwatt/cm4 °K


cwatt2/cm °K4


dwatt/cm2 °K4


View Answer watt/cm2 °K4

Log mean temperature difference in case of counter flow compared to parallel flow will be________________?


asame


bmore


cless


ddepends on other factors


View Answer more

According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to___________________?


aabsolute temperature


bsquare of temperature


cfourth power of absolute temperature


dfourth power of temperature



In free con-vection heat transfer, Nusselt number is function of________________?


aGrashoff no. and Reynold no


bGrashoff no and Prandtl no.


cPrandtl no. and Reynold no


dGrashoff no., Prandtl no and Reynold no



Which of the following property of air does not increase with rise in temperature ________________?


athermal conductivity


bthermal diffusivity


cdensity


ddynamic viscosity


View Answer density

The energy distribution of an ideal reflector at higher temperatures is largely in the range of ___________________?


ashorter wavelength


blonger wavelength


cremains same at all wavelengths


dwavelength has nothing to do with it


View Answer shorter wavelength

The value of Prandtl number for air is about _______________________?


a0.1


b0.3


c0.7


d1.7


View Answer 0.7

Total emissivity of polished silver compared to black body is___________________?


asame


bhigher


cmore or less same


dvery much lower


View Answer very much lower

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