Heat and Mass Transfer MCQs

Question 1

The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as

Accepted Answer

Kirchhoff's law

Answer

Wien's law

Answer

Stefan's law

Answer

Planck's law

Question 2

In free convection heat transfer, Nusselt number is function of

Accepted Answer

Grashoff number and Prandtl number

Answer

Grashoff number and Reynold number

Answer

Prandtl number and Reynold number

Answer

Grashoff number, Prandtl number and Reynold number

Question 3

In regenerator type heat exchanger, heat transfer takes place by

Accepted Answer

Flow of hot and cold fluids alternately over a surface

Answer

Direct mixing of hot and cold fluids

Answer

A complete separation between hot and cold fluids

Answer

Generation of heat again and again

Question 4

Heat flows from one body to other when they have

Accepted Answer

Different temperatures

Answer

Different heat contents

Answer

Different specific heat

Answer

Different atomic structure

Question 5

The ratio of the thickness of thermal boundary layer to the thickness of hydrodynamic boundary layer is equal to (Prandtl number) n, where n is equal to

Accepted Answer

$$ - \frac{1}{3}$$

Answer

$$ - \frac{2}{3}$$

Answer

1

Answer

$$-1$$

Question 6

Which of the following would lead to a reduction in thermal resistance?

Accepted Answer

All of the above

Answer

In conduction, reduction in the thickness of the material and an increase in thermal conductivity.

Answer

In convection, stirring of the fluid and cleaning the heating surface.

Answer

In radiation, increasing the temperature and reducing the emissivity.

Question 7

Heat transfer in liquid and gases takes place by

Accepted Answer

Convection

Answer

Conduction

Answer

Radiation

Answer

Conduction and convection

Question 8

According of Kirchhoff's law

Accepted Answer

Ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body

Answer

Radiant heat is proportional to fourth power of absolute temperature

Answer

Emissive power depends on temperature

Answer

Emissive power and absorptivity are constant for all bodies

Question 9

Thermal conductivity of wood depends on

Accepted Answer

All of the above

Answer

Moisture

Answer

Density

Answer

Temperature