Heat Transfer MCQs

Question 1

Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is

Accepted Answer

4.364

Answer

0.72

Answer

18

Answer

83

Question 2

Value of Nusselt number $$\left( {{	ext{Nu}} = \frac{{{	ext{hD}}}}{{	ext{k}}}} ight)$$ for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is

Accepted Answer

2

Answer

0.5

Answer

10

Answer

100

Question 3

What is the absorptivity of a black body?

Accepted Answer

1

Answer

0

Answer

0.78

Answer

0.95

Question 4

Vacuum is generally maintained in the vapour space of an evaporator mainly to

Accepted Answer

Get economical temperature difference by using moderate pressure steam

Answer

Facilitate forward feeding in multiple effect evaporation

Answer

Concentrate heat sensitive materials

Answer

Achieve very high concentration of the final product

Question 5

Prandtl and Reynold's analogies are identical for Prandtl number value of

Accepted Answer

1

Answer

0

Answer

0.5

Answer

5

Question 6

In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient

Accepted Answer

Decreases

Answer

Increases

Answer

Is not affected

Answer

May increase or decrease; depends on the feed

Question 7

Dietus-Boelter equation cannot be used for molten metals mainly due to its very low

Accepted Answer

Prandtl number

Answer

Grashoff number

Answer

Thermal conductivity

Answer

Viscosity

Question 8

A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,

Accepted Answer

Both B & C

Answer

The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant

Answer

Both the spheres will emit equal amount of radiation per unit time in the beginning

Answer

Both will absorb equal amount of radiation from the surrounding in the beginning

Question 9

Pick out the wrong statement.

Accepted Answer

The emissivity of a surface decreases, if it gets corroded by atmospheric environment

Answer

The emissivity of a surface increases with increase in surface roughness

Answer

The emissivity of a polished surface is quite low

Answer

The emissivity of a non-metallic surface decreases with increase in the temperature