Heat and Mass Transfer MCQs

Question 1

The value of the wavelength for maximum emissive power is given by

Accepted Answer

Wien’s law

Answer

Planck's law

Answer

Stefan's law

Answer

Fourier's law

Question 2

The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

Accepted Answer

Equal to one

Answer

Greater than one

Answer

Less than one

Answer

Equal to Nusselt number

Question 3

The emissivity for a black body is

Accepted Answer

1

Answer

0

Answer

0.5

Answer

0.75

Question 4

A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as

Accepted Answer

AU/Cmin

Answer

ACmin/U

Answer

U/ACmin

Answer

AUCmin

Question 5

Reynolds number is the ratio of

Accepted Answer

Inertia force to viscous force

Answer

Energy transferred by convection to that by conduction

Answer

Kinematic viscosity to thermal diffusivity

Answer

None of the above

Question 6

If the temperature of a solid surface changes form 27°C to 627°C, then its emissive power changes in the ratio of

Accepted Answer

81

Answer

3

Answer

9

Answer

270

Question 7

Kirchhoff's law states that

Accepted Answer

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

Answer

The total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature

Answer

The wave length corresponding to the maximum energy is proportional to the absolute temperature

Answer

None of the above

Question 8

Metals are good conductors of heat because

Accepted Answer

Their atoms collide frequently

Answer

Their atoms are relatively far apart

Answer

They contain free electrons

Answer

They have high density

Question 9

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

Accepted Answer

0.51

Answer

0.1

Answer

0.23

Answer

0.42