Mechanical Engineering MCQs

Page No. 150

The amount of radiation mainly depends on___________________?


anature of body


btemperature of body


ctype of surface of body


dall of the above


View Answer all of the above

Absorptivity of a body will be equal to its emissivity___________________?


aat all temperatures


bat one particular temperature


cwhen system is under thermal equi-librium


dat critical temperature



Depending on the radiating properties, body will be transparent when________________?


ap = 0, x = 0 and a = 1


bp=l,x = 0,anda = 0


cp = 0, T= l,anda = 0


dX = 0, a + p = 1


View Answer p = 0, T= l,anda = 0

Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by ___________________?


aconvection


bfree convection


cforced convection


dradiation


View Answer radiation

In regenerator type heat exchanger, heat transfer takes place by___________________?


adirect mixing of hot and cold fluids


ba complete separation between hot and cold fluids


cflow of hot and cold fluids alternately over a surface


dgeneration of heat again and again



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


a3


b6


c9


d81


View Answer 81

A perfect black body is one which_______________?


ais black in colour


breflects all heat


ctransmits all heat radiations


dabslprbs heat radiations of all wave lengths falling on it



Planck’s law holds good for________________?


ablack bodies


bpolished bodies


call coloured bodies


dall of the above


View Answer black bodies

A grey body is one whose absorptivity _________________?


avaries with temperature


bvaries with the wave length of incident ray


cvaries with both


ddoes not vary with temperature and wave length of the incident ray



The thermal diffusivities for gases are generally_____________________?


amore than those for liquids


bless than those for liquids


cmore than those for solids


ddependent on the viscosity



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