Heat Transfer MCQs

Question 1

As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient

Accepted Answer

Goes through a minimum

Answer

Continues to increase

Answer

Continues to decrease

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Goes through a maximum

Question 2

Heat transfer by natural convection is enhanced in system with

Accepted Answer

High co-efficient of thermal expansion

Answer

High viscosity

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Low temperature gradients

Answer

Low density change with temperature

Question 3

A black body when hot, emits heat radiation of __________ wavelengths.

Accepted Answer

All

Answer

Small

Answer

Large

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One fixed

Question 4

Pick out the wrong statement.

Accepted Answer

Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger

Answer

In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2

Answer

Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number

Answer

Hot gases at moderate pressure are usually in the shell side of shell and tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side

Question 5

Multipass heat exchangers are used

Accepted Answer

To obtain higher heat transfer co-efficient and shorter tube

Answer

Because of simplicity of fabrication

Answer

For low heat load

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To reduce the pressure drop

Question 6

Steam economy in case of a triple effect evaporator will be

Accepted Answer

> 1

Answer

1

Answer

< 1

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Between 0 and 1

Question 7

Kirchoff's law is applicable to

Accepted Answer

Both A and B

Answer

Monochromatic radiation only

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Total radiation only

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Only volumes and not to surfaces

Question 8

The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness)

Accepted Answer

∝ $$\frac{1}{{	ext{t}}}$$

Answer

∝ t

Answer

∝ $$\sqrt {	ext{t}} $$

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Independent of 't'

Question 9

The Grashoff number is defined as the ratio of the

Accepted Answer

Buoyancy to viscous forces

Answer

Buoyancy to inertial forces

Answer

Inertial to viscous forces

Answer

Buoyancy to surface tension forces