Heat Transfer (3151909) MCQs

MCQs of Convection

Showing 41 to 50 out of 51 Questions
41.

The hydrodynamic and thermal boundary layer are identical at Prandtl number equal to

(a)

0.5

(b)

1

(c)

10

(d)

50

Answer:

Option (b)

42.

The temperature gradient in the fluid flowing over a heated plate will be

(a)

zero at the plate surface 

(b)

positive at the surface 

(c)

very steep at the surface

(d)

zero at the top of the thermal boundary layer

Answer:

Option (d)

43.

For a fluid having Prandtl number equal to unity the hydrodynamic boundary layer thickness δ and thermal boundary layer thickness δt are related as 

(a)

δ=δt

(b)

δ>δt

(c)

δ<δt

(d)

δt =δ31

Answer:

Option (a)

44.

Heat is lost from a 100 mm diameter steam pipe placed horizontally in ambient air at 30°C. If the Nusselt number is 25 and the thermal conductivity of air is 0.03 w/m2K , then the heat transfer coefficient will be .............. w/m2K  

(a)

 


7.5

(b)

16.5

(c)

25

(d)

30

Answer:

Option (a)

45.

Which of the following properties of air does increase with rising in temperatures?

(a)

Thermal diffusivity 

(b)

Dynamic viscosity 

(c)

Density

(d)

Thermal conductivity

Answer:

Option (c)

46.

When all the conditions are identical, in the case of flow-through pipes with heat transfer, the velocity profiles will be identical for

(a)

liquid heating and liquid cooling

(b)

gas heating and gas cooling

(c)

liquid heating and gas cooling

(d)

heating and cooling of any fluid

Answer:

Option (d)

47.

When there is a flow of fluid over a plate of length 'L', The average heat transfer coefficient is given by ( Nux = local Nusselt number, other symbols have the usual meaning)

(a)

0L hx dx

(b)

ddx(hx)

(c)

1L 0L hx dx

(d)

kL 0L Nux dx

Answer:

Option (c)

48.

The overall heat transfer coefficient is used in problems of 

(a)

conduction

(b)

convection

(c)

radiation

(d)

conduction and convection

Answer:

Option (d)

49.

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles due to difference of density caused by temperature of the particle is known as

(a)

conduction

(b)

free convection

(c)

forced convection

(d)

radiation

Answer:

Option (b)

50.

The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as

(a)

conduction

(b)

free convection

(c)

forced convection

(d)

radiation

Answer:

Option (c)

Showing 41 to 50 out of 51 Questions