Heat and Mass Transfer MCQs

Question 1

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Accepted Answer

Conduction

Answer

Convection

Answer

Radiation

Answer

Both convection and conduction

Question 2

Wien’s law states that the wave length corresponding to ________ is proportional to the absolute temperature.

Accepted Answer

Maximum energy

Answer

Minimum energy

Answer

Both (A) and (B)

Answer

None of these

Question 3

The amount of radiation mainly depends on

Accepted Answer

All of the above

Answer

Nature of body

Answer

Temperature of body

Answer

Type of surface of body

Question 4

The heat transfer by conduction through a thick cylinder (Q) is given by (where T1 = Higher temperature, T2 = Lower temperature, r1 = Inside radius, r2 = Outside radius, $$l$$ = Length of cylinder and k = Thermal conductivity)

Accepted Answer

$${	ext{Q}} = \frac{{2\pi l{	ext{k}}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{2.3\log \left( {\frac{{{{	ext{r}}_2}}}{{{{	ext{r}}_1}}}} ight)}}$$

Answer

$${	ext{Q}} = \frac{{2.3\log \left( {\frac{{{r_2}}}{{{r_1}}}} ight)}}{{2\pi l{	ext{k}}\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}$$

Answer

$${	ext{Q}} = \frac{{2\pi \left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)}}{{2.3l{	ext{k}}\log \left( {\frac{{{{	ext{r}}_2}}}{{{{	ext{r}}_1}}}} ight)}}$$

Answer

$${	ext{Q}} = \frac{{2\pi l{	ext{k}}}}{{2.3\left( {{{	ext{T}}_1} - {{	ext{T}}_2}} ight)\log \left( {\frac{{{{	ext{r}}_2}}}{{{{	ext{r}}_1}}}} ight)}}$$

Question 5

Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, $$\rho $$ = Density of substance, S = Specific heat and k = Thermal conductivity)

Accepted Answer

$${	ext{h}} = \frac{{	ext{k}}}{{ho {	ext{S}}}}$$

Answer

$${	ext{h}} = \frac{{ho {	ext{S}}}}{{	ext{k}}}$$

Answer

$${	ext{h}} = \frac{{	ext{S}}}{{ho {	ext{k}}}}$$

Answer

$${	ext{h}} = \frac{{ho {	ext{k}}}}{{	ext{S}}}$$

Question 6

Which of the following is expected to have highest thermal conductivity?

Accepted Answer

Solid ice

Answer

Steam

Answer

Melting ice

Answer

Water

Question 7

Which of the following has maximum value of thermal conductivity?

Accepted Answer

Copper

Answer

Aluminium

Answer

Steel

Answer

Brass

Question 8

Free convection flow depends on

Accepted Answer

All of these

Answer

Density

Answer

Coefficient of viscosity

Answer

Gravitational force

Question 9

The critical thickness of insulation for a sphere is

Accepted Answer

2k/h0

Answer

k/h0

Answer

h0/k

Answer

h0/2k