In thermal radiation for a black body (where, Œµ is emissivity and Œ± is absorptivity)$

Œ± ‚â† 1, Œµ ‚â† 1

Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is

thin walled having the value of Ao Ai/< 2.

With increase in porosity, the thermal conductivity of a solid substance

may increase or decrease; depends on the solid

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45¬∞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.

Economy of a multiple effect evaporator is not influenced much by the

ratio of the weight of the thin liquor to thick liquor

Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place

from one part of a body to the another part of the same body.

between two bodies in physical contact with each other.

between two bodies not in physical contact with each other.

from one part of a body to the another part of the same body.

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the

wavelength of monochromatic radiation.

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

decreases the outlet temperature of cooling medium.

increases the overall heat transfer coefficient.

Rate of crystallisation does not depend upon the

turbulence within the solution.

number and active surface area of the crystals.

Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

shell and tube heat exchanger with air inside tubes and steam on shell side.

finned tube heat exchanger with air inside and steam outside.

finned tube heat exchanger with air outside and steam inside.

shell and tube heat exchanger with air inside tubes and steam on shell side.

shell and tube heat exchanger with air on shell side and steam inside tubes.

Kirchoff's law is applicable to

only volumes and not to surfaces

A 10 cm dia steam pipe, carrying steam at 180¬∞C, is covered with an insulation (conductivity = 0.6 W/m.¬∞C). It losses heat to the surroundings at 30¬∞C. Assume a heat transfer co-efficient of 0.8 W/m2.¬∞C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

equal to that of the uninsulated steam pipe.

greater than that for uninsulated steam pipe.

less than that of the uninsulated steam pipe.

equal to that of the uninsulated steam pipe.

less than the steam pipe with 5 cms insulation.

Which of the following is not used as a medium for high temperature heating ?

liquid metal (e.g. molten sodium)

fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)

In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient

may increase or decrease; depends on the feed

Increasing the liquor level in the evaporator results in the

increase in liquor film co-efficient.

decreased effect of hydrostatic head.

increased true temperature drop.

The steam ejector is used to

remove condensate from the steam pipelines.

If Prandtl number is greater than the Schmidt number, then the

concentration boundary layer lies inside the thermal boundary layer.

thermal boundary layer lies inside the concentration boundary layer.

concentration boundary layer lies inside the thermal boundary layer.

thermal & concentration boundary layers are of equal thickness.

hydrodynamic(i.e., momentum)boundary layer is thicker than the other two.

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

existence of thermal boundary layer.

temperature gradient produced due to density difference

buoyancy of the bubbles produced at active nucleation site.

The purpose of floating head in a heat exchanger is to

facilitate its lengthening, if needed.

The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

giving the surface a mirror finish.

painting the surface white (with aluminium paint).

giving the surface a mirror finish.

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

enhancing the fluid pumping rate.

keeping the heat transfer surface clean.

enhancing the fluid pumping rate.

640 + Mcqs in Heat Transfer in Chemical Engineering Page 11 McqOptions

501.	In thermal radiation for a black body (where, Œµ is emissivity and Œ± is absorptivity)$
A.	Œ± = 1; Œµ ‚â† 1
B.	Œ± ‚â† 1, Œµ = 1
C.	Œ± ‚â† 1, Œµ ‚â† 1
D.	Œ± = 1; Œµ = 1
Answer» E.

Discussion

502.	Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is
A.	thin walled having the value of Ao Ai/< 2.
B.	thick walled.
C.	having the value of Ao/Ai > 2.
D.	both (b) and (c).
Answer» B. thick walled.

Discussion

503.	In natural convection heat transfer, the correlating parameter is the
A.	Graetz number
B.	Eckert number
C.	Grashoff number
D.	Bond number
Answer» D. Bond number

Discussion

504.	In which mode of heat transfer, the Biot number is important ?
A.	Transient heat conduction
B.	Natural convection
C.	Forced convection
D.	Radiation
Answer» B. Natural convection

Discussion

505.	With increase in porosity, the thermal conductivity of a solid substance
A.	increases
B.	decreases
C.	remains unchanged
D.	may increase or decrease; depends on the solid
Answer» C. remains unchanged

Discussion

506.	Overall heat transfer co-efficient for cooling of hydrocarbons by water is about
A.	50 -100 Kcal/hr.m2.¬∞C
B.	50 -100 W/m2 . ¬∞K
C.	50 -100 BTU/hr. ft.2¬∞F
D.	1000 - 1500 BTU/hr. ft.2¬∞F
Answer» D. 1000 - 1500 BTU/hr. ft.2¬∞F

Discussion

507.	In a heat exchanger with steam outside the tubes, a liquid gets heated to 45¬∞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 45¬∞C
B.	more than 45¬∞C
C.	equal to 45¬∞C
D.	initially decreases and remains constant thereafter.
Answer» C. equal to 45¬∞C

Discussion

508.	The absorptivity of a body is equal to its emissivity
A.	at a particular temperature.
B.	for circular bodies.
C.	under thermal equilibrium.
D.	none of these.
Answer» D. none of these.

Discussion

509.	Low thermal conductivity of heat insulating materials is due to its
A.	dense structure.
B.	high proportion of air space.
C.	high specific heat.
D.	none of these.
Answer» C. high specific heat.

Discussion

510.	Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator.
A.	long tube
B.	falling film
C.	high pressure
D.	none of these
Answer» C. high pressure

Discussion

511.	Which of the following is unimportant in forced convection ?
A.	Reynolds number
B.	Prandtl number
C.	Grashhoff number
D.	none of these
Answer» D. none of these

Discussion

512.	Economy of a multiple effect evaporator is not influenced much by the
A.	boiling point elevations
B.	temperature of the feed
C.	rate of heat transfer
D.	ratio of the weight of the thin liquor to thick liquor
Answer» B. temperature of the feed

Discussion

513.	Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place
A.	between two bodies in physical contact with each other.
B.	between two bodies not in physical contact with each other.
C.	from one part of a body to the another part of the same body.
D.	both 'b' & 'c'
Answer» C. from one part of a body to the another part of the same body.

Discussion

514.	h.D/K is called the __________ number.
A.	Nusselt
B.	Peclet
C.	Rayleigh
D.	Grashoff
Answer» B. Peclet

Discussion

515.	Tube expansion allowances exist in __________ heat exchanger.
A.	multipass fixed tube sheet
B.	U-tube
C.	single pass fixed tube sheet
D.	none of these
Answer» C. single pass fixed tube sheet

Discussion

516.	The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.
A.	more
B.	less
C.	same
D.	unpredictable
Answer» C. same

Discussion

517.	Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent.
A.	1
B.	7
C.	18
D.	26
Answer» C. 18

Discussion

518.	As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the
A.	temperature of the body only.
B.	wavelength of monochromatic radiation.
C.	both (a) and (b).
D.	nature of material of body.
Answer» B. wavelength of monochromatic radiation.

Discussion

519.	A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of
A.	2
B.	20.8
C.	20.2
D.	20.5
Answer» C. 20.2

Discussion

520.	For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it
A.	decreases the pressure drop.
B.	decreases the outlet temperature of cooling medium.
C.	increases the overall heat transfer coefficient.
D.	none of these.
Answer» D. none of these.

Discussion

521.	Rate of crystallisation does not depend upon the
A.	extent of supersaturation.
B.	turbulence within the solution.
C.	number and active surface area of the crystals.
D.	none of these.
Answer» E.

Discussion

522.	The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is
A.	2
B.	43497
C.	4
D.	43556
Answer» E.

Discussion

523.	Viscous & heat sensitive liquids are concentrated in __________ evaporators.
A.	open pan
B.	long tube
C.	agitated film
D.	none of these
Answer» D. none of these

Discussion

524.	The Fourier number (defined as a.t/L2) is used in the analysis of problem involving heat transfer by
A.	forced convection
B.	natural convection
C.	transient conduction
D.	steady state conduction
Answer» D. steady state conduction

Discussion

525.	Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is
A.	finned tube heat exchanger with air inside and steam outside.
B.	finned tube heat exchanger with air outside and steam inside.
C.	shell and tube heat exchanger with air inside tubes and steam on shell side.
D.	shell and tube heat exchanger with air on shell side and steam inside tubes.
Answer» C. shell and tube heat exchanger with air inside tubes and steam on shell side.

Discussion

526.	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

527.	The energy radiated from a surface Q at absolute temperature T is related as
A.	Q ‚àù T2
B.	Q ‚àù T4
C.	Q ‚àù T3
D.	none of these
Answer» C. Q ‚àù T3

Discussion

528.	Kirchoff's law is applicable to
A.	monochromatic radiation only
B.	total radiation only
C.	both (a) and (b)
D.	only volumes and not to surfaces
Answer» D. only volumes and not to surfaces

Discussion

529.	Heat transfer by __________ may not necessarily require the presence of a medium.
A.	conduction
B.	natural convection
C.	forced convection
D.	radiation
Answer» E.

Discussion

530.	In a single effect evaporator, the economy is
A.	1
B.	< 1
C.	> 1
D.	none of these
Answer» C. > 1

Discussion

531.	The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
A.	Re.Gz
B.	Nu, Pr
C.	Nu, Pr, Re
D.	Nu, Gz
Answer» E.

Discussion

532.	In Fourier's law, the proportionality constant is called the
A.	heat transfer co-efficient
B.	thermal diffusivity
C.	thermal conductivity
D.	Stefan-Boltzman constant
Answer» D. Stefan-Boltzman constant

Discussion

533.	For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.
A.	extremely low
B.	low
C.	high
D.	no
Answer» D. no

Discussion

534.	What is Nusselt number ?
A.
B.
C.
D.
Answer» C.

Discussion

535.	A 10 cm dia steam pipe, carrying steam at 180¬∞C, is covered with an insulation (conductivity = 0.6 W/m.¬∞C). It losses heat to the surroundings at 30¬∞C. Assume a heat transfer co-efficient of 0.8 W/m2.¬∞C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be
A.	greater than that for uninsulated steam pipe.
B.	less than that of the uninsulated steam pipe.
C.	equal to that of the uninsulated steam pipe.
D.	less than the steam pipe with 5 cms insulation.
Answer» C. equal to that of the uninsulated steam pipe.

Discussion

536.	Which of the following is not used as a medium for high temperature heating ?
A.	Dowtherm
B.	mercury
C.	liquid metal (e.g. molten sodium)
D.	fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)
Answer» C. liquid metal (e.g. molten sodium)

Discussion

537.	Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam.
A.	0.4 - 0.6
B.	1-1.3
C.	1.8-2
D.	2 - 2.4
Answer» C. 1.8-2

Discussion

538.	In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient
A.	increases
B.	decreases
C.	is not affected
D.	may increase or decrease; depends on the feed
Answer» C. is not affected

Discussion

539.	Viscosity of gases __________ with increase in temperature.
A.	increase very rapidly
B.	increase slowly
C.	decrease slowly
D.	remain unaffected
Answer» C. decrease slowly

Discussion

540.	Duhring rule is important in solving problems on
A.	distillation
B.	crystallisation
C.	evaporation
D.	humidification
Answer» D. humidification

Discussion

541.	Increasing the liquor level in the evaporator results in the
A.	decreased capacity.
B.	increase in liquor film co-efficient.
C.	decreased effect of hydrostatic head.
D.	increased true temperature drop.
Answer» B. increase in liquor film co-efficient.

Discussion

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

Discussion

543.	The value of Stefan-Boltazman constant in SI unit is
A.	5.6697 x 10-8W/m2.¬∞K4
B.	0.1714 x 10-8W/m2.¬∞K4
C.	5.6697 x 10-8kcal/m2 . ¬∞K4
D.	0.1714 x 10-8kcal/m2. ¬∞K4
Answer» B. 0.1714 x 10-8W/m2.¬∞K4

Discussion

544.	The steam ejector is used to
A.	remove condensate from the steam pipelines.
B.	create vacuum.
C.	superheat the steam.
D.	none of these.
Answer» C. superheat the steam.

Discussion

545.	If Prandtl number is greater than the Schmidt number, then the
A.	thermal boundary layer lies inside the concentration boundary layer.
B.	concentration boundary layer lies inside the thermal boundary layer.
C.	thermal & concentration boundary layers are of equal thickness.
D.	hydrodynamic(i.e., momentum)boundary layer is thicker than the other two.
Answer» B. concentration boundary layer lies inside the thermal boundary layer.

Discussion

546.	A dephlegmator is a
A.	total condenser
B.	vacuum evaporator
C.	partial condenser
D.	double pipe heat exchanger
Answer» D. double pipe heat exchanger

Discussion

547.	Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the
A.	existence of thermal boundary layer.
B.	temperature gradient produced due to density difference
C.	buoyancy of the bubbles produced at active nucleation site.
D.	none of these.
Answer» E.

Discussion

548.	The purpose of floating head in a heat exchanger is to
A.	avoid buckling of tubes.
B.	provide support for tubes.
C.	decrease the pressure drop.
D.	facilitate its lengthening, if needed.
Answer» B. provide support for tubes.

Discussion

549.	The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by
A.	painting the surface black.
B.	painting the surface white (with aluminium paint).
C.	giving the surface a mirror finish.
D.	roughening the surface.
Answer» C. giving the surface a mirror finish.

Discussion

550.	Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by
A.	keeping the heat transfer surface clean.
B.	enhancing the fluid pumping rate.
C.	increasing the tube length.
D.	none of these.
Answer» B. enhancing the fluid pumping rate.

Discussion

Explore topic-wise MCQs in Chemical Engineering.

In thermal radiation for a black body (where, Œµ is emissivity and Œ± is absorptivity)$

Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is

In natural convection heat transfer, the correlating parameter is the

In which mode of heat transfer, the Biot number is important ?

With increase in porosity, the thermal conductivity of a solid substance

Overall heat transfer co-efficient for cooling of hydrocarbons by water is about

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45¬∞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$

The absorptivity of a body is equal to its emissivity

Low thermal conductivity of heat insulating materials is due to its

Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator.

Which of the following is unimportant in forced convection ?

Economy of a multiple effect evaporator is not influenced much by the

Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place

h.D/K is called the __________ number.

Tube expansion allowances exist in __________ heat exchanger.

The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.

Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent.

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the

A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

Rate of crystallisation does not depend upon the

The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is

Viscous & heat sensitive liquids are concentrated in __________ evaporators.

The Fourier number (defined as a.t/L2) is used in the analysis of problem involving heat transfer by

Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

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

The energy radiated from a surface Q at absolute temperature T is related as

Kirchoff's law is applicable to

Heat transfer by __________ may not necessarily require the presence of a medium.

In a single effect evaporator, the economy is

The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are

In Fourier's law, the proportionality constant is called the

For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.

What is Nusselt number ?

Which of the following is not used as a medium for high temperature heating ?

Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam.

In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient

Viscosity of gases __________ with increase in temperature.

Duhring rule is important in solving problems on

Increasing the liquor level in the evaporator results in the

'Duhring's plot' is of use in

The value of Stefan-Boltazman constant in SI unit is

The steam ejector is used to

If Prandtl number is greater than the Schmidt number, then the

A dephlegmator is a

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

The purpose of floating head in a heat exchanger is to

The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

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