MCQs of Convection (Heat Transfer - 3151909)

Heat Transfer (3151909) MCQs

MCQs of Convection

Showing 21 to 30 out of 51 Questions

21.

A body cooling from 80 $°$ C to 70 $°$ C takes 10 minutes when left exposed to cool further from 70 $°$ C to 60 $°$ C under the same external conditions it will take

(a)	same time of 10 minutes
(b)	more than 10 minutes
(c)	less than 10 minutes
(d)	time will depend upon the environmental conditions

22.

A hot metal piece kept in the air cools from $80 ° C$ to $70 ° C$ in $t_{1}$ seconds from $70 ° C$ to $60 ° C$ in $t_{2}$ seconds and from $60 ° C$ to $50 ° C$ in $t_{3}$ seconds then

(a)	$t_{1} = t_{2} = t_{3}$
(b)	$t_{1} < t_{2} < t_{3}$
(c)	$t_{1} > t_{2} > t_{3}$
(d)	the relationship between, $t_{2}$ and $t_{3}$ will depend upon the material of the hot piece

23.

Free convection heat flow depends on all of the followings, except

(a)	density
(b)	coefficient of viscosity
(c)	gravitational force
(d)	velocity

24.

The free convection heat transfer is significantly affected by

(a)	Reynolds number
(b)	Grashoff number
(c)	Prandtl number
(d)	Stanton number

25.

Consider natural convection heat transfer between a vertical tube surface and a fluid surrounding it. For dimensional analysis of the problem, the characteristic length corresponds to

(a)	length of the tube
(b)	diameter of the tube
(c)	the perimeter of the tube
(d)	either length or diameter of the tube

26.

The Nusselt number in convective heat transfer

(a)	signifies the velocity gradient at the surface
(b)	is the ratio of conduction to convection resistance
(c)	represents the ratio of viscous to inertia force
(d)	is the ratio of molecular momentum diffusivity to thermal diffusivity

27.

The Nusselt number in the natural transfer is a function of fluid Prandtl number and

(a)	Stanton number
(b)	Biot number
(c)	Grashoff number
(d)	Reynolds number

28.

On a summer day, a scooter rider feels more comfortable while on the move than while at a stoplight because

(a)	an object in motion captures less radiation
(b)	air has a low specific heat and hence it is cooler
(c)	air is transparent to radiation and hence it is cooler than the body
(d)	more heat is by convection and radiation while in motion

29.

The ratio of heat transfer by convection to that by conduction is called

(a)	Stanton number
(b)	Nusselt number
(c)	Biot number
(d)	Peclet number

30.

Prandtl number is

(a)	a measure of the temperature gradient at the surface
(b)	the ratio of conduction to convection resistance
(c)	the ratio of molecular momentum diffusivity to thermal diffusivity
(d)	mass diffused to momentum diffused

Showing 21 to 30 out of 51 Questions