Heat Transfer MCQs

Question 1

For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number)

Accepted Answer

$${	ext{N}}_{{	ext{Pr}}}^{\frac{1}{3}}$$

Answer

NPr

Answer

$${	ext{N}}_{{	ext{Pr}}}^{ - 1}$$

Answer

$${	ext{N}}_{{	ext{Pr}}}^{ - \frac{1}{3}}$$

Question 2

The critical radius 'r' of insulation on a pipe is given by

Accepted Answer

$${	ext{r}} = \frac{{	ext{k}}}{{	ext{h}}}$$

Answer

$${	ext{r}} = \frac{{2{	ext{k}}}}{{	ext{h}}}$$

Answer

$${	ext{r}} = \frac{{	ext{k}}}{{2{	ext{h}}}}$$

Answer

$${	ext{r}} = \frac{{	ext{h}}}{{	ext{k}}}$$

Question 3

Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by

Accepted Answer

Keeping the heat transfer surface clean

Answer

Enhancing the fluid pumping rate

Answer

Increasing the tube length

Answer

None of these

Question 4

Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface?

Accepted Answer

Interfacial tension

Answer

Liquid density

Answer

Liquid viscosity

Answer

Hot surface temperature

Question 5

Leidenfrost point is a term concerned with the

Accepted Answer

Boiling of a liquid on a hot surface

Answer

Condensation of the saturated vapor on a cold surface

Answer

Concentration of a corrosive solution by evaporation

Answer

Heat transfer between two highly viscous liquids

Question 6

The unit of conductance in SI unit is

Accepted Answer

W/°K

Answer

W/m

Answer

W/m2

Answer

W/m°K

Question 7

With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer

Accepted Answer

Decreases

Answer

Increases

Answer

Increases exponentially

Answer

Remains unaffected

Question 8

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the

Accepted Answer

Temperature gradient produced due to density difference

Answer

Existence of thermal boundary layer

Answer

Buoyancy of the bubbles produced at active nucleation site

Answer

None of these

Question 9

For a multipass shell and tube heat exchanger, the LMTD correction factor is always

Accepted Answer

< 1

Answer

1

Answer

> 1

Answer

Between 1 & 2