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Heat Transfer MCQ Questions & Answers

Heat Transfer MCQs : This section focuses on the "Heat Transfer". These Multiple Choice Questions (MCQs) should be practiced to improve the Heat Transfer skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.




Question 1

Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively)

A. C/E
B. E/C
C. CE

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Question 2

The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K= 0.04 W/m.°K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is - 5°C. The outside wall temperature is

A. 25°C
B. 30°C
C. 35°C
D. 40°C

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Question 3

The sun emits light having maximum intensity at a wavelength 468nm. Assume emissivity of sun is 1. Calculate its surface temperature. σ= 5.67*10-8W/m2K4.

A. 6800K
B. 3400K
C. 6196K
D. 7200K

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Question 4

Ratio of convection heat transfer to conduction is known as?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number

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Question 5

The electromagnetic energy emitted by a perfect radiator corresponding to a temperature T and surface area A is?

A. AσT4Δt, in unit time Δt
B. AeσT4Δt, in unit time Δt
C. Ae4 c) AeσT4
D. AσT4

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Question 6

Ratio of buoyancy to viscous forces is known as?

A. Prandtl number
B. Grashof number
C. Colburn factor
D. Nusselt number

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Question 7

Rate of heat flow in conduction.

A. Is directly proportional to temperature gradient
B. Is inversely proportional to temperature gradient
C. Does not depend on temperature gradient
D. Does not depend on temperature gradient & inversely proportional to temperature gradient

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Question 8

Ratio of inertia to viscous forces is known as?

A. Stanton number
B. Prandtl number
C. Rayleigh number
D. Reynolds number

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Question 9

Two spheres, A & B, are made up of the same material. The radius of A is twice that of B, while the temperature of A is half that of B. What is their ratio of energy emitted per unit time (EA : EB)?

A. 1
B. 1/4
C. 1/2
D. 1/16

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Question 10

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is

A. in the central core of the fluid.
B. uniformly distributed throughout the fluid.
C. mainly confined to a thin film of fluid near the surface.
D. none of these.

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Question 11

Ratio of pressure drop for internal flow through ducts is known as?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number

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Question 12

For solids and liquids, specific heat

A. depends on the process
B. is independent of the process
C. may or may not depend on the process
D. none of the mentioned

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Question 13

Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.

A. laminar
B. transition
C. both 'a' & 'b'
D. highly turbulent

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Question 14

With increase in temperature, the thermal conductivity of non-metallic amorphous solids

A. decreases
B. increases
C. remains constant
D. first decreases upto certain temperature and then increases

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Question 15

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)

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Question 16

Shell side pressure drop in a shell and tube heat exchanger does not depend upon the

A. baffle spacing & shell diameter.
B. tube diameter & pitch.
C. viscosity, density & mass velocity of shell side fluid.
D. none of these.

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Question 17

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

A. higher economy
B. lower capacity
C. both (a) & (b)
D. lower economy

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Question 18

Quantitatively heat conduction can be described as?

A. Heat flow for a given temperature difference
B. Time rate of heat flow for a given temperature difference
C. Temperature difference caused due to heat flow per unit time
D. Temperature difference per unit quantity of heat transferred

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Question 19

Heat and work are

A. path functions
B. inexact differentials
C. depend upon the path followed
D. all of the mentioned

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Question 20

The unit of heat transfer co-efficient in SI unit is

A. J/M2°K
B. W/m2°K
C. W/m°K
D. J/m°K

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Question 21

In case of evaporators, liquid entrainment results primarily due to

A. high vacuum in the evaporator.
B. high evaporation rate.
C. foaming of the solution.
D. high heat transfer rate.

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Question 22

What is the expression for heat current? Q is heat, t is time, T is temperature.

A. ΔQ/Δt
B. ΔQ/ΔT
C. ΔT/Δt
D. ΔQ/ΔTΔt

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Question 23

Fouling factor

A. is a dimensionless quantity.
B. does not provide a safety factor for design.
C. accounts for additional resistances to heat flow.
D. none of these.

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Question 24

Leidenfrost point is a term concerned with the

A. condensation of the saturated vapor on a cold surface.
B. concentration of a corrosive solution by evaporation.
C. heat transfer between two highly viscous liquids.
D. boiling of a liquid on a hot surface.

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Question 25

Ratio of molecular diffusivity to thermal diffusivity is also known as?

A. Biot number
B. Prandtl number
C. Rayleigh number
D. Biot number

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Question 26

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.

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Question 27

A steel and a copper bar are joined end to end. The area of the steel bar is half the area of the copper bar. Their lengths are equal to 10cm each. Temperature of free ends of steel & copper rod are 0°C & 100°C respectively. KS = 50 J/smK & KC =384 J/smK. Calculate equivalent thermal conductivity of the combined bar.

A. 63°C
B. 63K
C. 336°C
D. 36K

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Question 28

What is the net amount of energy per unit time being received by a body having a temperature of 40 °C in a surrounding of 60°C? (The surface area of body = 2m2, σ = 5.67*10-8W/ m2K4 & emissivity of 0.4).

A. 122.4W
B. 0.47W
C. 33W
D. 86W

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Question 29

Which of the following is true?

A. latent heat of fusion is not much affected by pressure
B. latent heat of vaporization is highly sensitive to pressure
C. both of the mentioned
D. none of the mentioned

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Question 30

The transfer of heat between two bodies in direct contact is called

A. radiation
B. convection
C. conduction
D. none of the mentioned

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Question 31

Product of Prandtl number and Reynolds number is also known as?

A. Peclet number
B. Prandtl number
C. Rayleigh number
D. Biot number

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Question 32

A process stream of dilute aqueous solution flowing at the rate of10 Kg.s-1 is to be heated. Steam condensate at 95°C is available for heating purpose, also at a rate of 10 Kg.s-1. A 1 - 1 shell and tube heat exchanger is available. The best arrangement is

A. counter flow with process stream on shell side.
B. counter flow with process stream on tube side.
C. parallel flow with process stream on shell side.
D. parallel flow with process stream on tube side.

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Question 33

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

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Question 34

Fourier's law applies to the heat transfer by

A. convection
B. radiation
C. conduction
D. all (a), (b) & (c)

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Question 35

The steam ejector is used to

A. remove condensate from the steam pipelines.
B. create vacuum.
C. superheat the steam.
D. none of these.

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Question 36

Pick out the wrong statement.

A. Orifice baffles are never used in a shell and tube heat exchanger.
B. Pressure drop on the shell side of a heat exchanger depends upon tube pitch also.
C. In a horizontal tube evaporator, surface blanketing by air is avoided.
D. Split ring type and pull through type floating heads are two commonly used floating heads is heat exchangers.

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Question 37

Heat waves

A. can not pass through vacuum.
B. travel in straight line.
C. can be reflected by a mirror.
D. both (b) and (c).

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Question 38

In a heat exchanger, floating head is provided to

A. facilitate cleaning of the exchanger.
B. increase the heat transfer area.
C. relieve stresses caused by thermal expansion.
D. increase log mean temperature gradient.

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Question 39

Latent heat is taken at

A. constant temperature
B. constant pressure
C. both of the mentioned
D. none of the mentioned

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Question 40

The actual temperature drop across the heating surface in an evaporator depends on the

A. feed.
B. depth of liquid over heating surface.
C. pressure difference between steam chest and vapour space.
D. all (a), (b) and (c).

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Question 41

At a given temperature a body emits energy of a single wavelength corresponding to that temperature. True or False?

A. True
B. False

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Question 42

Crystal size in a continuous crystalliser depends upon the

A. rate of heat transfer.
B. degree of turbulence.
C. degree of supersaturation.
D. all (a), (b) and (c).

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Question 43

Heat produced when a steady state current, I passes through an electrical conductor having resistance, 'R' is

A. IR
B. I2R
C. IR2
D. I2R2

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Question 44

For an ideal black body

A. absorptivity = 1
B. reflectivity = 1
C. emissivity = 0
D. transmissivity = 1

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Question 45

In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is

A. 40.5
B. 34.4
C. 26.8
D. 25

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Question 46

For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area

A. increases
B. decreases
C. remains constant
D. passes through a maxima

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Question 47

Which of the following is known as the dimensionless heat transfer coefficient?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Weber number

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Question 48

When water is kept in a very hot pan, the entire water heats up. Which mode of heat transfer is responsible for this?

A. Conduction
B. Convection
C. Radiation
D. Convection along with radiation

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Question 49

Kirchoff s law applies to __________ radiation.

A. total
B. monochromatic
C. both (a) & (b)
D. neither (a) nor (b)

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Question 50

Black liquor generated during paper manufacture is concentrated in a

A. single effect evaporator.
B. single effect evaporator followed by a crystalliser.
C. multiple effect evaporator.
D. multiple effect evaporators followed by a crystalliser.

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Question 51

Air is best heated with steam in a heat exchanger of

A. plate type.
B. double pipe type with fin on steam side.
C. double pipe type with fin on air side.
D. shell and tube type.

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Question 52

Reynold's analogy states that

A. Nst α f
B. Nst α NRe
C. NNu α f
D. NRe α f

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Question 53

Which of the following is known as the dimensionless heat transfer coefficient?

A. Friction factor
B. Grashof number
C. Nusselt number
D. Prandtl number

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Question 54

Baffles in the shell side of a shell and tube heat exchanger

A. increase the cross-section of the shell side liquid.
B. force the liquid to flow parallel to the bank.
C. increase the shell side heat transfer co-efficient.
D. decrease the shell side heat transfer co-efficient.

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Question 55

Thermal conductivity of a conducting solid material depends upon its

A. temperature
B. porosity
C. both (a) & (b)
D. neither (a) nor (b)

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Question 56

Heat flow into a system is taken to be ____, and heat flow out of the system is taken as ____

A. positive, positive
B. negative, negative
C. negative, positive
D. positive, negative

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Question 57

Pick out the wrong statement.

A. In case of heat transfer by purely forced convection, GR/Re2 ≤ 1.
B. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as 'x') is equal to 4x.
C. Distillation process is not the same as evaporation.
D. The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface.

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Question 58

Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer.

A. no
B. the least
C. the largest
D. lower

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Question 59

The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film )

A. (ΔT)2
B. ΔT
C. (ΔT)1/4
D. (ΔT)3/2

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Question 60

The specific heat of the substance is defined as the amount of heat required to raise a unit mass of the substance through a unit rise in temperature.

A. TRUE
B. FALSE

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Question 61

Presence of a non-condensing gas in a condensing vapour

A. increases the rate of condensation.
B. decreases thermal resistance.
C. is desirable to increase the film co-efficient.
D. none of these.

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Question 62

Air is best heated with steam in a heat exchanger of

A. shell and tube type
B. plate type
C. double pipe type with fin on steam side
D. double pipe type with fin on air side

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Question 63

The number of kg vaporised per kg of steam fed to the evaporator is defined as

A. capacity
B. rate of evaporation
C. economy
D. rate of vaporisation

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Question 64

Product of Grashof and Prandtl is known as?

A. Peclet number
B. Biot number
C. Rayleigh number
D. Reynolds number

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Question 65

Select the correct statement.

A. Radiation doesn’t require any medium
B. Convection involves heat transfer by vibration of particles at their position
C. Conduction involves movement of particles to transfer heat
D. Radiation is responsible for heat of gas flame heating the cooking pan

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Question 66

If we hold a metal rod from one end and dip the other in a source of fire, what will happen to the temperature of the rod at steady state?

A. Be uniform
B. Decrease with time
C. Remain constant at a single value throughout the length of the rod
D. Stay nonuniform

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Question 67

When vaporisation takes place directly at the heating surface, it is called

A. film boiling
B. nucleate boiling
C. vapour binding
D. none of these

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Question 68

Ratio of rate of heat conduction to the rate of internal energy storage is in solid is known as?

A. Biot number
B. Drag coefficient
C. Eckert number
D. Fourier number

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Question 69

Heat transfer and work transfer are

A. boundary phenomena
B. energy interactions
C. energy in the transit
D. all of the mentioned

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Question 70

Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately

A. 32
B. 37
C. 45
D. 50

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Question 71

The equivalent diameter for pressure drop is __________ that for heat transfer.

A. smaller than
B. greater than
C. equal to
D. not related with

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Question 72

Which of the following is concerned with both heat and mass transfer ?

A. Lewis relationship
B. Nusselt number
C. Kutateladze number
D. Froude number

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Question 73

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.

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Question 74

The transfer of heat between a wall and a fluid system in motion is called

A. radiation
B. convection
C. conduction
D. none of the mentioned

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Question 75

What is the value of Wien’s constant?

A. 2.9*10-3mK
B. 2.9*10-4mK
C. 2.9*10-3cmK
D. 2.9*10-4cmK

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Question 76

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.

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Question 77

Pick out the wrong statement.

A. The controlling resistance in case of heating of air by condensing steam is in the air film.
B. The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant temperature.
C. In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs.
D. Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature.

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Question 78

Which of the following is generally considered as opaque surface towards radiations?

A. Gases
B. Solids
C. Liquids
D. Both (b) and (c)

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Question 79

In the equation, dQ=TdX

A. dQ is an inexact differential
B. dX is an exact differential
C. X is an extensive property
D. all of the mentioned

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