Heat Transfer MCQs

Question 1

A __________ surface has the maximum thermal emissivity out of the following.

Accepted Answer

Black & rough

Answer

Black & smooth

Answer

White & smooth

Answer

White & rough

Question 2

Which of the following has maximum thermal conductivity at the same temperature?

Accepted Answer

Steel

Answer

Petrol

Answer

Air

Answer

All of the above

Question 3

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the

Accepted Answer

Temperature of the body only

Answer

Wavelength of monochromatic radiation

Answer

Both A and B

Answer

Nature of material of body

Question 4

With increase in temperature, the thermal conductivity of fresh lubricating oil

Accepted Answer

Decreases

Answer

Increases

Answer

Remains unchanged

Answer

May increase or decrease; depends on its composition

Question 5

'Fouling factor' used in the design of a multipass shell and tube heat exchanger is a

Accepted Answer

Factor of safety

Answer

Non-dimensional factor

Answer

Conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient

Answer

None of these

Question 6

In a gas-liquid shell and tube heat exchanger, the

Accepted Answer

All of the above

Answer

Presence of a non-condensible gas decreases the condensing film co-efficient

Answer

Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature

Answer

Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes

Question 7

In SI units, thermal conductivity is expressed in

Accepted Answer

Watt/m.°K

Answer

Watt/m2.°K

Answer

Watt/m3.°K

Answer

Watt/m4.°K

Question 8

With increase in temperature, the thermal conductivity of most liquids

Accepted Answer

Decreases

Answer

Increases

Answer

Remains same

Answer

First increases upto a certain temperature and then becomes constant

Question 9

Which of the following has the lowest overall heat transfer co-efficient?

Accepted Answer

Air

Answer

Dowtherm

Answer

Molten sodium

Answer

Water