Mechanical Engineering MCQs

Page No. 155

The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be ________________?


aI


b0.5


c2


d0.25


View Answer 2

Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in _________________?


aelectric heater


bsteam condenser


cmelting of ice


dboiler


View Answer boiler

Thermal conductivity of a material may be defined as the________________?


aquantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C


bquantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C


cheat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces


dall of the above


View Answer all of the above

Which of the following is expected to have highest thermal conductivity_______________?


asteam


bsolid ice


cmelting ice


dwater


View Answer solid ice

In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by ________________?


ahr (time)


bsqm (area)


c°C (temperature)


dcm (thickness)


View Answer cm (thickness)

The time constant of a thermocouple is_______________?


athe time taken to attain the final temperature to be measured


bthe time taken to attain 50% of the value of initial temperature difference


cthe time taken to attain 63.2% of the value of initial temperature difference


ddetermined by the time taken to reach 100°C from 0°C



Thermal conductivity of water at 20°C is of the order of_____________________?


a0.1


b0.23


c0.42


d0.51


View Answer 0.51

Total heat is the heat required to__________________?


achange vapour into liquid


bchange liquid into vapour


cincrease the temperature of a liquid or vapour


dconvert water into steam and superheat it



Thermal conductivity of air with rise in temperature__________________?


aincreases


bdecreases


cremains constant


dmay increase or decrease depending on temperature


View Answer increases

Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of__________________?


a0.002


b0.02


c0.01


d0.1


View Answer 0.02

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