Heat transfer co-efficient equation for forced convection, Nu = 0.023 R e 0.8 . P r n , is not valid, if the value of

Reynolds number for the flow involved is > 10000.

Reynolds number for the flow involved is < 2100.

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45Â°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be

initially decreases and remains constant thereafter.

One kilogram of water at 0Â°C is changed to superheated steam of one atm pressure and 300Â° C. The major heat consumption in the process will be to

heat the water from 0Â°C to 100Â°C.

data insufficient, can't be predicted

The thermal boundary layer at N Pr > 1

and the hydrodynamic boundary layer are identical.

is thicker than hydrodynamic boundary layer.

is thinner than hydrodynamic boundary layer.

and the hydrodynamic boundary layer are identical.

Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212Â°F may be around __________ BTU.

data insufficient, can't be predicted

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m 2 .Â°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

lower pressure drop through the exchanger is desired.

higher condensing film co-efficient is desired.

condensate is corrosive in nature.

lower pressure drop through the exchanger is desired.

temperature of the incoming vapor is very high.

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50Â°C in industrial practice mainly to avoid

decrease in heat exchanger efficiency

At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : The thermal conductivity of material I

can be greater than or smaller than that of II.

For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively h f and h d , then

h f could be greater or smaller than h d

A body cools down from 75Â°C to 70Â°C in 10 minutes. It will cool down from 70Â° C to 65Â° C in __________ minutes.

either (b) or (c), depends on the mass of the body

75 + Mcqs in Heat Transfer in Chemical Engineering Page 1 McqOptions

1.	The purpose of providing a \'catchall\' in the vapor line of an evaporator is to
A.	regulate the vapor flow
B.	create vacuum
C.	arrest the entrained liquid
D.	vent the non-condensible gases
Answer» D. vent the non-condensible gases

Discussion

2.	In a trimetric drawing, the relationship of the angle between axes to each other is:
A.	two are equal
B.	three are equal
C.	none of the above
D.	three are unequal
Answer» D. three are unequal

Discussion

3.	What is the geometric mean of two heat transfer areas A 1 and A 2 ?
A.	A 1 . A 2
B.	A 1 + A 2
C.	A 1 . A 2
D.	2 A 1 . A 2
Answer» E.

Discussion

4.	In a laboratory test run, the rate of drying was found to be 0.5 x 10 -3 kg/m 2 .s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m 2 /kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is
A.	2000
B.	4000
C.	5000
D.	6000
Answer» D. 6000

Discussion

5.	The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U 0 = 400 W/m 2 .K. The fouling factor after one year of operation is found to be h d0 = 2000 W/m 2 .K. The overall heat transfer co-efficient at this time is
A.	1200W/m 2 .K
B.	894W/m 2 .K
C.	333W/m 2 .K
D.	287 W/m 2 .K
Answer» D. 287 W/m 2 .K

Discussion

6.	Heat transfer co-efficient equation for forced convection, Nu = 0.023 R e 0.8 . P r n , is not valid, if the value of
A.	n = 0.4 is used for heating.
B.	n = 0.3 is used for cooling.
C.	Reynolds number for the flow involved is > 10000.
D.	Reynolds number for the flow involved is < 2100.
Answer» E.

Discussion

7.	In a heat exchanger with steam outside the tubes, a liquid gets heated to 45Â°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
A.	less than 45Â°C
B.	more than 45Â°C
C.	equal to 45Â°C
D.	initially decreases and remains constant thereafter.
Answer» C. equal to 45Â°C

Discussion

8.	Duhring's plot' is of use in
A.	extractive distillation
B.	evaporation
C.	leaching
D.	absorption
Answer» C. leaching

Discussion

9.	Value of Nusselt number [ Nu = ( hD / k )] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is
A.	0.5
B.	2
C.	10
D.	100
Answer» C. 10

Discussion

10.	The inner wall of a furnace is at a temperature of 700Â°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m -1 .Â°C -1 respectively. The ambient air is at 30Â°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m -2 .Â°C -1 . The rate of heat loss from the outer surface in W.m -2 is
A.	165.4
B.	167.5
C.	172.5
D.	175
Answer» B. 167.5

Discussion

11.	The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h 0 = heat transfer coefficient at the outer surface)
A.	K / h 0
B.	2 K / h 0
C.	h 0 / K
D.	h 0 / 2K
Answer» C. h 0 / K

Discussion

12.	A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are k A and k B and the specific heat capacities are C PA and C PB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when
A.	C PA > C PB
B.	C PA < C PB
C.	k A < 0.5 k B
D.	k A >2 k B
Answer» D. k A >2 k B

Discussion

13.	The radiation heat flux from a heating element at a temperature of 800Â°C, in a furnace maintained at 300Â°C is 8 kW/m 2 . The flux, when the element temperature is increased to 1000Â°C for the same furnace temperature is
A.	11.2 kW/m 2
B.	12.0 kW/m 2
C.	14.6 kW/m 2
D.	16.5 kW/m 2
Answer» E.

Discussion

14.	If h 1 = inner film co-efficient and / h 2 = outer film co-efficient, then the overall heat transfer co-efficient is
A.	always less than h 1
B.	always between h 1 and h 2
C.	always higher than h 2
D.	dependent on metal resistance
Answer» C. always higher than h 2

Discussion

15.	One kilogram of water at 0Â°C is changed to superheated steam of one atm pressure and 300Â° C. The major heat consumption in the process will be to
A.	heat the water from 0Â°C to 100Â°C.
B.	evaporate the water.
C.	to superheat the steam.
D.	data insufficient, can't be predicted
Answer» C. to superheat the steam.

Discussion

16.	Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m 2 Â°C.
A.	10-50
B.	100-500
C.	1000-1500
D.	5000-15000
Answer» E.

Discussion

17.	Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by This is valid for the value of N Re equal to
A.	< 2100
B.	2100-4000
C.	> 4000
D.	> 10000
Answer» E.

Discussion

18.	The left face of a one dimensional slab of thickness 0.2 m is maintained at 80Â°C and the right face is exposed to air at 30Â°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m 2 .K. At steady state, the temperature of the right face in Â°C is
A.	77.2
B.	71.2
C.	63.8
D.	48.7
Answer» E.

Discussion

19.	The thermal boundary layer at N Pr > 1
A.	is thicker than hydrodynamic boundary layer.
B.	is thinner than hydrodynamic boundary layer.
C.	and the hydrodynamic boundary layer are identical.
D.	disappears.
Answer» C. and the hydrodynamic boundary layer are identical.

Discussion

20.	A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of materialA is twice that of B. Under the equilibrium, the temperature difference across the wall is 36Â°C. The temperature difference across the layer A is __________ Â°C.
A.	6
B.	12
C.	18
D.	24
Answer» C. 18

Discussion

21.	Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212Â°F may be around __________ BTU.
A.	180
B.	970
C.	3.97
D.	data insufficient, can't be predicted
Answer» B. 970

Discussion

22.	is termed as the __________ number.
A.	Grashoff
B.	Nusselt
C.	Prandtl
D.	Stanton
Answer» D. Stanton

Discussion

23.	The equation, ( N St x N 2/3 Pr ) = f /2, is the __________ analogy.
A.	Colburn
B.	Reynolds
C.	Prandtl
D.	none of these.
Answer» B. Reynolds

Discussion

24.	Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. Â°C respectively are joined together. The temperature outside of A and C are 30Â°C and 100Â°C respectively. The interface between B and C will be at a temperature of __________ Â°C.
A.	40
B.	95
C.	70
D.	50
Answer» D. 50

Discussion

25.	The average heat transfer co-efficient over the entire length of the plate ( h a ) and the local heat transfer co-efficient ( h L ), in case of heat transfer over a flat plate in lminar zone is related as
A.	h a = 0.8 h L
B.	h a = 2 h L
C.	h a = h L
D.	h a = 5 h L
Answer» C. h a = h L

Discussion

26.	A long iron rod initially at a temperature of 20Â°C has one end dipped in boiling water (100Â°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40Â°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time
A.	t = 283 s
B.	t = 356 s
C.	t = 400 s
D.	t = 800 s
Answer» E.

Discussion

27.	Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m 2 .Â°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the
A.	higher condensing film co-efficient is desired.
B.	condensate is corrosive in nature.
C.	lower pressure drop through the exchanger is desired.
D.	temperature of the incoming vapor is very high.
Answer» C. lower pressure drop through the exchanger is desired.

Discussion

28.	The equation, N st = f /2, is the __________ analogy.
A.	Colburn
B.	Reynolds
C.	Prandtl
D.	none of these
Answer» C. Prandtl

Discussion

29.	is called the __________ number
A.	Peclet
B.	Stanton
C.	Graetz
D.	none of these
Answer» D. none of these

Discussion

30.	A steel sphere of radius 0.1 m at 400Â°K is immersed in an oil at 300Â°K. If the centre of the sphere reaches 350Â°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.
A.	5 minutes
B.	10 minutes
C.	20 minutes
D.	40 minutes
Answer» B. 10 minutes

Discussion

31.	( N Gr x N Pr ) is called the __________ number.
A.	Graetz
B.	Reyleigh
C.	Nusselt
D.	Stanton
Answer» C. Nusselt

Discussion

32.	In case of surface condensers, a straight line is obtained on plotting __________ on an ordinary graph paper.
A.	1/ -0.8
B.	-0.8
C.	-2
D.	1/ -2
Answer» B. -0.8

Discussion

33.	The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50Â°C in industrial practice mainly to avoid
A.	its evaporation loss
B.	excessive corrosion
C.	uneconomic LMTD
D.	decrease in heat exchanger efficiency
Answer» C. uneconomic LMTD

Discussion

34.	The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences ( ?T ) between wall and outside bulk. The proportionality is given as
A.	( ?T ) 1/4
B.	?T 1/2
C.	( ?T ) 5/4
D.	( ?T ) 3/4
Answer» E.

Discussion

35.	1000 Kg of liquid at 30Â°C in a well stirred vessel has to be heated to 120Â°C, using immersed coils carrying condensing steam at 150Â°C. The area of the steam coils is 1.2 m 2 and the overall heat transfer co-efficient to the liquid is 1500 W/m 2 .Â°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.Â°C, the time taken for the liquid to reach desired temperature will be
A.	15 min
B.	22 min
C.	44 min
D.	51 min
Answer» E.

Discussion

36.	A metal ball of radius 0.1 m at a uniform temperature of 90Â°C is left in air at 30Â°C. The density and the specific heat of the metal are 3000 kg/m 3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m 2 .K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60Â°C is
A.	555
B.	55.5
C.	0.55
D.	0.15
Answer» E.

Discussion

37.	At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : The thermal conductivity of material I
A.	is smaller than that of II.
B.	is greater than that of II.
C.	is equal to that of II.
D.	can be greater than or smaller than that of II.
Answer» B. is greater than that of II.

Discussion

38.	For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively h f and h d , then
A.	h f = h d
B.	h f > h d
C.	h f < h d
D.	h f could be greater or smaller than h d
Answer» D. h f could be greater or smaller than h d

Discussion

39.	Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500Â°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for
A.	cube
B.	cylinder
C.	sphere
D.	equal for all the three
Answer» B. cylinder

Discussion

40.	A BTU/hr.ft. 2 Â°F is equal to
A.	1 kcal/hr. m 2 Â°C.
B.	4.88 kcal/hr. m. 2 Â°C.
C.	1 kcal/hr. m 2 .Â°K.
D.	none of these.
Answer» C. 1 kcal/hr. m 2 .Â°K.

Discussion

41.	For a laminar flow of fluid in a circular tube, ' h 1 ' is the convective heat transfer co-efficient at velocity ' V 1 '. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is
A.	1.26 h 1
B.	0.794 h 1
C.	0.574 h 1
D.	1.741 h 1
Answer» C. 0.574 h 1

Discussion

42.	A sphere of radius ' R 1 ' is enclosed in a sphere of radius ' R 2 '. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is
A.	0
B.	R2 /( R 1 + R 2 )
C.	1
D.	( R 1 / R 2 ) 2
Answer» C. 1

Discussion

43.	Overall heat transfer co-efficient of a particular tube is U 1 . If the same tube with some dirt deposited on either side has coefficient U 2 , then
A.	U 1 = U 2
B.	U 2 > U 1
C.	U 1 > U 2
D.	U 1 = dirt factor - U 2
Answer» B. U 2 > U 1

Discussion

44.	Walls of a cubical oven are of thickness l , and they are made of material of thermal conductivity k . The temperature inside the oven is 100Â°C and the inside heat transfer co-efficient is 3 k / l . If the wall temperature on the outside is held at 25Â°C, what is the inside wall temperature in degree centigrade ?
A.	35.5
B.	43.75
C.	81.25
D.	48.25
Answer» D. 48.25

Discussion

45.	Heat transfer by radiation between two bodies at T 1 & T 2 and in an ambient temperature of T a Â°C depends on
A.	T 1 - T 2
B.	T 1 - T a
C.	T 2 - T a
D.	none of these
Answer» E.

Discussion

46.	1 BTU/hr.ft.Â°F is equal to __________ kcal/hr. m.Â°C.
A.	1.49
B.	1
C.	4.88
D.	none of these
Answer» B. 1

Discussion

47.	The critical radius of insulation for cylindrical pipe is (where, h i = heat transfer coefficient at inside of the pipe )
A.	K / h 0
B.	2K / h 0
C.	h i / K
D.	2h i / K
Answer» B. 2K / h 0

Discussion

48.	A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200Â°K, then the temperature drop (in Â°K) across the layer of material 'A' is
A.	125
B.	133
C.	150
D.	160
Answer» E.

Discussion

49.	A body cools down from 75Â°C to 70Â°C in 10 minutes. It will cool down from 70Â° C to 65Â° C in __________ minutes.
A.	10
B.	>10
C.	<10
D.	either (b) or (c), depends on the mass of the body
Answer» C. <10

Discussion

50.	A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300Â°C and allowed to cool in natural air. Which one will cool the slowest ?
A.	Cube
B.	Plate
C.	Sphere
D.	All will cool at the same rate
Answer» D. All will cool at the same rate

Discussion

Explore topic-wise MCQs in Chemical Engineering.

The purpose of providing a \'catchall\' in the vapor line of an evaporator is to

In a trimetric drawing, the relationship of the angle between axes to each other is:

What is the geometric mean of two heat transfer areas A 1 and A 2 ?

The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U 0 = 400 W/m 2 .K. The fouling factor after one year of operation is found to be h d0 = 2000 W/m 2 .K. The overall heat transfer co-efficient at this time is

Heat transfer co-efficient equation for forced convection, Nu = 0.023 R e 0.8 . P r n , is not valid, if the value of

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45Â°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be

Duhring's plot' is of use in

Value of Nusselt number [ Nu = ( hD / k )] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is

The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h 0 = heat transfer coefficient at the outer surface)

The radiation heat flux from a heating element at a temperature of 800Â°C, in a furnace maintained at 300Â°C is 8 kW/m 2 . The flux, when the element temperature is increased to 1000Â°C for the same furnace temperature is

If h 1 = inner film co-efficient and / h 2 = outer film co-efficient, then the overall heat transfer co-efficient is

One kilogram of water at 0Â°C is changed to superheated steam of one atm pressure and 300Â° C. The major heat consumption in the process will be to

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m 2 Â°C.

Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by This is valid for the value of N Re equal to

The thermal boundary layer at N Pr > 1

Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212Â°F may be around __________ BTU.

is termed as the __________ number.

The equation, ( N St x N 2/3 Pr ) = f /2, is the __________ analogy.

Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. Â°C respectively are joined together. The temperature outside of A and C are 30Â°C and 100Â°C respectively. The interface between B and C will be at a temperature of __________ Â°C.

The average heat transfer co-efficient over the entire length of the plate ( h a ) and the local heat transfer co-efficient ( h L ), in case of heat transfer over a flat plate in lminar zone is related as

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m 2 .Â°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

The equation, N st = f /2, is the __________ analogy.

is called the __________ number

( N Gr x N Pr ) is called the __________ number.

In case of surface condensers, a straight line is obtained on plotting __________ on an ordinary graph paper.

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50Â°C in industrial practice mainly to avoid

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences ( ?T ) between wall and outside bulk. The proportionality is given as

At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : The thermal conductivity of material I

For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively h f and h d , then

A BTU/hr.ft. 2 Â°F is equal to

For a laminar flow of fluid in a circular tube, ' h 1 ' is the convective heat transfer co-efficient at velocity ' V 1 '. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is

A sphere of radius ' R 1 ' is enclosed in a sphere of radius ' R 2 '. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

Overall heat transfer co-efficient of a particular tube is U 1 . If the same tube with some dirt deposited on either side has coefficient U 2 , then

Heat transfer by radiation between two bodies at T 1 & T 2 and in an ambient temperature of T a Â°C depends on

1 BTU/hr.ft.Â°F is equal to __________ kcal/hr. m.Â°C.

The critical radius of insulation for cylindrical pipe is (where, h i = heat transfer coefficient at inside of the pipe )

A body cools down from 75Â°C to 70Â°C in 10 minutes. It will cool down from 70Â° C to 65Â° C in __________ minutes.

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300Â°C and allowed to cool in natural air. Which one will cool the slowest ?