Mechanical Engineering MCQs

Page No. 153

A steam pipe is to be insulated by two insulating materials put over each other . For best results__________________?


abetter insulation should be put over pipe and better one over it


binferior insulation should be put over pipe and better one over it


cboth may be put in any order


dwhether to put inferior OIL over pipe or the better one would depend on steam temperature



In heat exchangers, degree of approach is defined as the difference between temperatures of________________?


acold water inlet and outlet


bhot medium inlet and outlet


chot medium outlet and cold water inlet


dhot medium outlet and cold water outlet



Emissivity of a white polished body in comparison to a black body is________________?


ahigher


blower


csame


ddepends upon the shape of body


View Answer lower

Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of____________________?


a1 :1


b2: 1


c1 : 2


d4 : 1


View Answer 1 : 2

Heat conducted througfi unit area and unit thick face per unit time when temperature difference between opposite faces is unity,is called__________________?


athermal resistance


bthermal coefficient


ctemperature gradient


dthermal conductivity


View Answer thermal conductivity

The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as ________________?


aemissivity


btransmissivity


creflectivity


dintensity of radiation



In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by___________________?


aconvection


bradiation


cconduction


dboth convection and conduction


View Answer conduction

Unit of thermal diffusivity is_________________?


am2/hr


bm2/hr°C


ckcal/m2 hr


dkcal/m.hr°C


View Answer m2/hr

Film coefficient is defined as Inside diameter of tube________________?


aEquivalent thickness of film


bThermal conductivity Equivalent thickness of film Specific heat x Viscocity


cThermal conductivity Molecular diffusivity of momentum Thermal diffusivity


dFilm coefficient x Inside diameter Thermalconductivity



Thermal conductivity of wood depends on_______________?


amoisture


bdensity


ctemperature


dall of the above


View Answer all of the above

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