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
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
Question 2
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.
Question 3
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
Question 4
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.
Question 5
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.
Question 6
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.
Question 7
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.
Question 8
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.
Question 9
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.
Question 10
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
Question 11
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
Question 12
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).
Question 13
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
Question 14
For an ideal black body
A. absorptivity = 1
B. reflectivity = 1
C. emissivity = 0
D. transmissivity = 1
Question 15
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
Question 16
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.
Question 17
Fourier's law applies to the heat transfer by
A. convection
B. radiation
C. conduction
D. all (a), (b) & (c)
Question 18
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
Question 19
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).
Question 20
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
Question 21
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.
Question 22
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.
Question 23
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
Question 24
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.
Question 25
Kirchoff s law applies to __________ radiation.
A. total
B. monochromatic
C. both (a) & (b)
D. neither (a) nor (b)
Question 26
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.
Question 27
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.
Question 28
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.
Question 29
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.
Question 30
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.
Question 31
Reynold's analogy states that
A. Nst α f
B. Nst α NRe
C. NNu α f
D. NRe α f
Question 32
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.
Question 33
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
Question 34
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).
Question 35
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
Question 36
The equivalent diameter for pressure drop is __________ that for heat transfer.
A. smaller than
B. greater than
C. equal to
D. not related with
Question 37
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
Question 38
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
Question 39
The steam ejector is used to
A. remove condensate from the steam pipelines.
B. create vacuum.
C. superheat the steam.
D. none of these.
Question 40
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
Question 41
Thermal conductivity of a conducting solid material depends upon its
A. temperature
B. porosity
C. both (a) & (b)
D. neither (a) nor (b)
Question 42
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
Question 43
Which of the following is concerned with both heat and mass transfer ?
A. Lewis relationship
B. Nusselt number
C. Kutateladze number
D. Froude number
Question 44
Which of the following is generally considered as opaque surface towards radiations?
A. Gases
B. Solids
C. Liquids
D. Both (b) and (c)
Question 45
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)
Question 46
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
Question 47
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
Question 48
Heat and work are
A. path functions
B. inexact differentials
C. depend upon the path followed
D. all of the mentioned
Question 49
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
Question 50
Heat transfer and work transfer are
A. boundary phenomena
B. energy interactions
C. energy in the transit
D. all of the mentioned
Question 51
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
Question 52
Latent heat is taken at
A. constant temperature
B. constant pressure
C. both of the mentioned
D. none of the mentioned
Question 53
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
Question 54
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
Question 55
The transfer of heat between two bodies in direct contact is called
A. radiation
B. convection
C. conduction
D. none of the mentioned
Question 56
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
Question 57
Product of Grashof and Prandtl is known as?
A. Peclet number
B. Biot number
C. Rayleigh number
D. Reynolds number
Question 58
Product of Prandtl number and Reynolds number is also known as?
A. Peclet number
B. Prandtl number
C. Rayleigh number
D. Biot number
Question 59
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
Question 60
Ratio of buoyancy to viscous forces is known as?
A. Prandtl number
B. Grashof number
C. Colburn factor
D. Nusselt number
Question 61
Ratio of convection heat transfer to conduction is known as?
A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number
Question 62
Ratio of inertia to viscous forces is known as?
A. Stanton number
B. Prandtl number
C. Rayleigh number
D. Reynolds number
Question 63
Ratio of molecular diffusivity to thermal diffusivity is also known as?
A. Biot number
B. Prandtl number
C. Rayleigh number
D. Biot number
Question 64
Ratio of pressure drop for internal flow through ducts is known as?
A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number
Question 65
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
Question 66
Which of the following is known as the dimensionless heat transfer coefficient?
A. Friction factor
B. Grashof number
C. Colburn factor
D. Weber number
Question 67
Which of the following is known as the dimensionless heat transfer coefficient?
A. Friction factor
B. Grashof number
C. Nusselt number
D. Prandtl number
Question 68
At a given temperature a body emits energy of a single wavelength corresponding to that temperature. True or False?
A. True
B. False
Question 69
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
Question 70
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
Question 71
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
Question 72
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
Question 73
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
Question 74
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
Question 75
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
Question 76
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
Question 77
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
Question 78
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
Question 79
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
Question 80
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
Question 81
Pick out the wrong statement.
A. Reciprocal of the resistance to heat flow is called thermal conductance
B. Unit of thermal conductance is W/°K
C. Thermal conductance of a wall of thickness
D. None of these
Question 82
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 36°C. The temperature difference across the layer A is __________ °C.
A. 6
B. 12
C. 18
D. 24
Question 83
It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is
A. > 0.75
B. < 0.75
C. < 0.50
D. < 0.25
Question 84
In a forward feed multiple effect, the pressure build up will be
A. Least at the inlet of the first effect
B. Least at the outlet of the last effect
C. Highest at the inlet of the last effect
D. Highest at the outlet of the last effect
Question 85
With increase in temperature, the thermal conductivity of a gas
A. Increases
B. Decreases
C. Remains same
D. May increase or decrease depending on the type of gas
Question 86
With increase in temperature, the thermal conductivity of steel
A. Increases
B. Decreases
C. Remains unchanged
D. Increases exponentially
Question 87
A diathermaneous substance __________ the thermal radiation completely.
A. Absorbs
B. Reflects
C. Transmits
D. None of these
Question 88
For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in
A. Increased economy
B. Decreased economy
C. Lower capacity
D. No effect on economy
Question 89
Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m² .°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
Question 90
If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will
A. Increase by 1.8 times
B. Decrease by 22
C. Increase by 216
D. Remain unchanged
Question 91
The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of 'n' is exactly 4 for
A. Black painted bodies only
B. All bodies
C. Polished bodies only
D. A black body
Question 92
Convective heat transfer, in which heat is transferred by movement of warmed matter is described by
A. Fourier's law
B. Newton's law of cooling
C. Fick's law
D. None of these
Question 93
Viscosity of gases __________ with increase in temperature.
A. Increase very rapidly
B. Increase slowly
C. Decrease slowly
D. Remain unaffected
Question 94
The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as
A. (D)-1.8
B. (D)-0.2
C. (D)0.2
D. (D)1.8
Question 95
Pick out the wrong statement.
A. Heat transfer by radiation can not occur across an absolute volume
B. In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bundle between baffles
C. Propagation velocity for travel of heat radiation through vacuum is equal to the velocity of the light
D. The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same
Question 96
According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor)
A. 2f
B. f
C. f/2
D. f/4
Question 97
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
Question 98
Heat transfer rate described by Fourier's law will decrease, if the __________ increases.
A. Thermal conductivity
B. Thickness
C. Temperature difference
D. Heat transfer area
Question 99
In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased.
A. Velocity of circulation
B. Liquor-film co-efficient
C. Both A and B
D. Neither A and B
Question 100
In forced convection, the heat transfer depends on
A. Re, Pr
B. Re, Gr
C. Mainly Gr
D. Re only
Question 101
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
Question 102
The equation, Nst = f/2, is the __________ analogy.
A. Colburn
B. Reynolds
C. Prandtl
D. None of these
Question 103
The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy.
A. Colburn
B. Reynolds
C. Prandtl
D. None of these
Question 104
In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat exchanger.
A. Once
B. Twice
C. Thrice
D. Four times
Question 105
In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side __________ the heat transfer rate.
A. Increases
B. Decreases
C. Does not affect
D. May increase or decrease, depends on the type of baffle
Question 106
Radiator of an automobile engine is a __________ type of heat exchanger.
A. Co-current
B. Cross-current
C. Counter-current
D. Direct contact
Question 107
Trap is used to remove __________ from steam pipe lines.
A. Steam
B. Condensate
C. Non-condensables
D. None of these
Question 108
A graph between __________ is called Wilson plot.
A. 1/U Vs . 1/v0.8
B. 1/v0.8 Vs . U
C. V0.8 Vs . U
D. 1/U Vs . 1/V
Question 109
Pick out the wrong statement.
A. Swenson-Walker crystalliser is a batch crystalliser
B. Super saturation of the solution is the driving potential for a crystal growth
C. The liquor left after the removal of crystals from a solution is called mother liquor
D. The first stage of crystal formation is called nucleation
Question 110
The separation of liquid droplets from the vapor is done by a/an __________ , in the evaporators.
A. Steam ejector
B. Entrainment separator
C. Compressor
D. Vacuum pump
Question 111
The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoffs law.
A. Wavelength of radiation
B. Nature of the body
C. Temperature of the body
D. None of these
Question 112
Heat flux, as defined in heat flow is analogous to __________ in electricity flow.
A. Current
B. Voltage
C. Resistance
D. None of these
Question 113
The film thickness for laminar film condensation on vertical surface __________ from top to bottom.
A. Cummulatively increases
B. Cummulatively decreases
C. Remains constant
D. And the surface conductance increase
Question 114
The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.
A. Average
B. Geometric mean
C. Product
D. Sum
Question 115
For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then
A. hf = hd
B. hf > hd
C. hf < hd
D. hf could be greater or smaller than hd
Question 116
A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m².K. The Biot number is
A. 5.6
B. 0.025
C. 3.5
D. 0.0035
Question 117
A 2-4 heat exchanger involves
A. Only counter-flow of fluids
B. Only parallel-flow of fluids
C. Both counter and parallel-flow of the fluids
D. Smaller pressure drop compared to 1-2 exchanger
Question 118
A BTU/hr.ft.2 °F is equal to
A. 1 kcal/hr. m²°C
B. 4.88 kcal/hr. m.2°C
C. 1 kcal/hr. m².°K
D. None of these
Question 119
A dephlegmator is a
A. Total condenser
B. Vacuum evaporator
C. Partial condenser
D. Double pipe heat exchanger
Question 120
Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is
A. 0.72
B. 4.364
C. 18
D. 83
Question 121
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
Question 122
What is the absorptivity of a black body?
A. 1
B. 0
C. 0.78
D. 0.95
Question 123
Vacuum is generally maintained in the vapour space of an evaporator mainly to
A. Get economical temperature difference by using moderate pressure steam
B. Facilitate forward feeding in multiple effect evaporation
C. Concentrate heat sensitive materials
D. Achieve very high concentration of the final product
Question 124
Prandtl and Reynold's analogies are identical for Prandtl number value of
A. 0
B. 0.5
C. 1
D. 5
Question 125
Dietus-Boelter equation cannot be used for molten metals mainly due to its very low
A. Prandtl number
B. Grashoff number
C. Thermal conductivity
D. Viscosity
Question 126
A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,
A. The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
B. Both the spheres will emit equal amount of radiation per unit time in the beginning
C. Both will absorb equal amount of radiation from the surrounding in the beginning
D. Both B & C
Question 127
Pick out the wrong statement.
A. The emissivity of a surface decreases, if it gets corroded by atmospheric environment
B. The emissivity of a surface increases with increase in surface roughness
C. The emissivity of a polished surface is quite low
D. The emissivity of a non-metallic surface decreases with increase in the temperature
Question 128
An ejector is used to
A. Increase pressure
B. Increase temperature
C. Remove condensate
D. None of these
Question 129
An insulator should have
A. Low thermal conductivity
B. High thermal conductivity
C. Less resistance to heat flow
D. A porous structure
Question 130
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
Question 131
For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it
A. Occupies smaller space
B. Is more economical
C. Is easy to operate and maintain
D. All of the above
Question 132
In a heat exchanger, one transfer unit means
A. A section of the exchanger in which change in temperature of one stream equals the average driving force in the section
B. The size of the exchanger in which heat transfer rate is 1 kcal/hr
C. Both A and B
D. None of these
Question 133
When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?
A. At high fluid velocity
B. At low velocity
C. When fluid flows past a smooth surface
D. None of these
Question 134
__________ chart is known as transient heat conduction chart.
A. Dirhing's
B. Heisler's
C. Mollier's
D. Cox
Question 135
It is not preferable to use superheated steam in evaporators, because of its very
A. High temperature
B. High pressure
C. Low film co-efficient
D. None of these
Question 136
Vent pipes are provided in a condenser to
A. Remove non-condensable gases
B. Purge the condenser
C. Facilitate easy cleaning of tubes
D. None of these
Question 137
Electro-magnetic spectrum range, which is important for radiation varies from __________ microns.
A. 1 to 100
B. 0.5 to 50
C. 10 to 100
D. 100 to 1000
Question 138
Which of the following has the lowest Prandtl number?
A. Molten sodium (a coolant used in fast breeder reactor)
B. Water
C. Transformer oil
D. Dilute H₂SO₄
Question 139
Which has the lowest Prandtl number?
A. Liquid metal
B. Aqueous solution
C. Water
D. Lube oil
Question 140
For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would
A. Decrease
B. Increase
C. First decrease and then increase
D. First increase and then decrease
Question 141
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
Question 142
Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger?
A. Tube side pressure drop and the heat transfer rate
B. Convective heat transfer co-efficient
C. Effective tube surface area for convective heat transfer
D. All of the above
Question 143
Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger?
A. Corrosiveness
B. Fouling characteristic
C. Viscosity
D. None of these
Question 144
The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature)
A. (ΔT)²
B. (ΔT)⁴
C. (ΔT)³
D. √(ΔT)
Question 145
For small temperature difference, the heat transfer rate as per Newton's law of cooling is proportional to (where, Δt = excess temperature)
A. Δt
B. Δt²
C. Δt³
D. √Δt
Question 146
__________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side.
A. Single pass, fixed tube sheet
B. U-tube
C. Three pass, fixed tube sheet
D. None of these
Question 147
Which of the following has the highest thermal conductivity?
A. Brick
B. Air
C. Water
D. Silver
Question 148
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
Question 149
Radiant energy received by a body is proportional to (where, d = the distance between the object emitting radiation and that receiving it.)
A. √d
B. d
C. d2
D. d1.5
Question 150
The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe )
A. K/h0
B. 2K/h0
C. hi/K
D. 2hi/K
Question 151
In case of __________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface.
A. Nucleate
B. Local
C. Pool
D. Saturated
Question 152
Pick out the correct statement.
A. Higher is the temperature of the radiating body, higher is the wavelength of radiation
B. Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder
C. The wavelength corresponding to maximum mono-chromatic emissive power increases with rise in temperature
D. Solid angle subtended by the finite surface at the radiating element is called the angle of incidence
Question 153
Steady state one dimensional heat flow by conduction as given by Fourier's low does not assume that
A. There is no internal heat generation
B. Boundary surfaces are isothermal
C. Material is anisotropic
D. Constant temperature gradient exists
Question 154
Steam traps are provided in steam carrying pipelines to
A. Condense steam
B. Release excess steam pressure by bleeding steam
C. Remove condensate and inert gases
D. None of these
Question 155
In sub-cooled boiling,
A. Temperature of the heating surface is less than the boiling point of the liquid
B. Temperature of the heating surface is more than the boiling point of the liquid
C. Bubbles from heating surface are absorbed by the mass of the liquid
D. Very large vapour space is necessary
Question 156
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
Question 157
Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity?
A. Aluminium foil
B. Refractory bricks
C. Iron plate
D. Coke breeze
Question 158
As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient
A. Continues to increase
B. Continues to decrease
C. Goes through a minimum
D. Goes through a maximum
Question 159
Heat transfer by natural convection is enhanced in system with
A. High viscosity
B. High co-efficient of thermal expansion
C. Low temperature gradients
D. Low density change with temperature
Question 160
A black body when hot, emits heat radiation of __________ wavelengths.
A. Small
B. Large
C. All
D. One fixed
Question 161
Pick out the wrong statement.
A. In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2
B. Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number
C. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger
D. Hot gases at moderate pressure are usually in the shell side of shell and tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side
Question 162
Multipass heat exchangers are used
A. Because of simplicity of fabrication
B. For low heat load
C. To obtain higher heat transfer co-efficient and shorter tube
D. To reduce the pressure drop
Question 163
Steam economy in case of a triple effect evaporator will be
A. 1
B. < 1
C. > 1
D. Between 0 and 1
Question 164
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
Question 165
The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness)
A. ∝ t
B. ∝ 1/t
C. ∝ √t
D. Independent of 't'
Question 166
The Grashoff number is defined as the ratio of the
A. Buoyancy to inertial forces
B. Buoyancy to viscous forces
C. Inertial to viscous forces
D. Buoyancy to surface tension forces
Question 167
A __________ surface has the maximum thermal emissivity out of the following.
A. Black & smooth
B. Black & rough
C. White & smooth
D. White & rough
Question 168
Which of the following has maximum thermal conductivity at the same temperature?
A. Steel
B. Petrol
C. Air
D. All of the above
Question 169
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
Question 170
Fouling factor' used in the design of a multipass shell and tube heat exchanger is a
A. Non-dimensional factor
B. Factor of safety
C. Conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient
D. None of these
Question 171
In a gas-liquid shell and tube heat exchanger, the
A. Presence of a non-condensible gas decreases the condensing film co-efficient
B. Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature
C. Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes
D. All of the above
Question 172
In SI units, thermal conductivity is expressed in
A. Watt/m.°K
B. Watt/m². °K
C. Watt/m². °K
D. Watt/m4. °K
Question 173
With increase in temperature, the thermal conductivity of most liquids
A. Increases
B. Decreases
C. Remains same
D. First increases upto a certain temperature and then becomes constant
Question 174
Which of the following has the lowest overall heat transfer co-efficient?
A. Dowtherm
B. Molten sodium
C. Water
D. Air
Question 175
Pick out the correct statement.
A. 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F
B. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity
C. In unsteady state heat conduction, heat flows in the direction of temperature rise
D. In heat transfer by forced convection, Grashoff number is very important
Question 176
Value of Prandtl number for water ranges from
A. L to 2
B. 5 to 10
C. 100 to 500
D. 1000 to 2000
Question 177
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
Question 178
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
Question 179
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
Question 180
Boiling point elevation of a solution of NaOH
A. Increases rapidly with temperature rise
B. Is almost independent of temperature
C. Is almost independent of pressure
D. Both B and C
Question 181
In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always
A. < 1
B. > 1
C. 1
D. ∞
Question 182
In counter flow compared to parallel flow,
A. LMTD is greater
B. Less surface area is required for a given heat transfer rate
C. Both A and B
D. More surface area is required for a given heat transfer rate
Question 183
Pick out the wrong statement.
A. Heat transfer from a hot body to cold body by the emission of heat waves is called radiation
B. Filmwise condensation takes place on non-wettable surfaces
C. The boiling point of a solution is affected by liquid head as well as boiling point elevation
D. None of these
Question 184
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
Question 185
At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe?
A. 0.5
B. < 0.5
C. > 0.6
D. < 0.1
Question 186
Rate of heat transfer by vaporisation from pools of water is affected by the
A. Nature of heating surface and distribution of bubbles
B. Surface tension of water
C. Viscosity of water
D. All of the above
Question 187
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
Question 188
The Stefan-Boltzman constant depends on the
A. Medium
B. Temperature
C. Surface
D. None of these
Question 189
In an extended surface heat exchanger, fluid having lower co-efficient
A. Flows through the tube
B. Flows outside the tubes
C. Can flow either inside or outside the tubes
D. Should not be used as it gives very high pressure drop
Question 190
Which of the following has maximum thermal conductivity?
A. Iron
B. Coal
C. Nitrogen
D. Tar
Question 191
For specified tube outside diameter, higher BWG means higher
A. Tube thickness
B. Cross-sectional area
C. Weight per unit length
D. None of these
Question 192
Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube
A. Exit-fluid temperature > wall temperature
B. Exit fluid temperature < wall temperature
C. Exit fluid temperature = wall temperature
D. Graetz number > 100
Question 193
Which of the following has the minimum thermal conductivity?
A. Nitrogen
B. Steel
C. Carbon black
D. Tar
Question 194
A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°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 40°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
Question 195
Fresh orange juice contains 12% (by weight) solids and the rest water 90% of the fresh juice is sent to an evaporator to remove water and subsequently mixed with the remaining 10% of fresh juice. The resultant product contains 40% solids. The kg of water removed from 1 kg fresh juice is
A. 0.4
B. 0.5
C. 0.6
D. 0.7
Question 196
Heat transfer occurs by natural convection because change in temperature causes difference in
A. Viscosity
B. Density
C. Thermal conductivity
D. Heat capacity
Question 197
In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is
A. Minimum
B. Maximum
C. Zero
D. Infinity
Question 198
The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the
A. Solution has an elevation of boiling point
B. Evaporators operate under vacuum
C. Evaporators opreate at atmospheric pressure
D. None of these
Question 199
Choose the most important factor on which the heat conducted through a wall in a unit time will depend on?
A. Thickness of the wall
B. Area of the wall perpendicular to heat flow
C. Material of the wall
D. Temperature difference between the two surfaces of the wall
Question 200
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 of the above
Question 201
Kg of liquid evaporated per hour in an evaporator is defined as its
A. Capacity
B. Economy
C. Steam load
D. None of these
Question 202
Mechanical recompression evaporation is used in the production of
A. Alcohol
B. Distilled water
C. Salt
D. Fruits jam
Question 203
Reason for operating an evaporator in multiple effect is to secure
A. Increased steam economy
B. Decreased steam consumption
C. Both A and B
D. Increased capacity
Question 204
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
Question 205
Pick out the wrong statement.
A. Economy of a multiple effect evaporator is not influenced by the boiling point elevation
B. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature
C. Double pipe heat exchangers are mostly used in the field of refrigeration
D. Finned tube heat exchangers are suitable for heating air by steam
Question 206
Grashoff number, which is defined as g . β(Ts - T∞) ρ². L³/μ², is proportional to the ratio of buoyancy force to __________ force.
A. Viscous
B. Elastic
C. Inertial
D. None of these
Question 207
For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.
A. Extremely low
B. Low
C. High
D. No
Question 208
__________ paint has the minimum absorption co-efficient.
A. Black
B. White lead
C. Grey
D. Light cream
Question 209
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
Question 210
In a shell and tube heat exchanger, the shell side fluid velocity can not be changed by changing the
A. Tube layout
B. Tube diameter
C. Tube pitch
D. No. of baffles
Question 211
Indirect contact heat exchangers are preferred over direct contact heat exchangers, because
A. Heat transfer co-efficient are high
B. There is no risk of contamination
C. There is no mist formation
D. Cost of equipment is lower
Question 212
A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the __________ number.
A. Condensation
B. Grashoff
C. Stantan
D. Brinkman
Question 213
Nucleate boiling is promoted
A. On polished surfaces
B. On rough surfaces
C. In the absence of agitation
D. None of these
Question 214
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
Question 215
If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid
A. Remains unchanged
B. Increases
C. Increases or decreases depending on number of shell passes
D. Decreases
Question 216
A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in __________ minutes.
A. 10
B. >10
C. <10
D. Either B or C, depends on the mass of the body
Question 217
Circulation pump is located below the evaporater to
A. Avoid cavitation
B. Avoid frequent priming
C. Create more suction head
D. None of these
Question 218
Dropwise condensation occurs on __________ surfaces.
A. Clean and dirt free
B. Smooth clean
C. Contaminated cooling
D. Polished
Question 219
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
Question 220
__________ equation relates the thermal conductivity of a solid to its temperature.
A. Antonie
B. Kopp's
C. Lee's
D. Kistyakowski
Question 221
In case of heat flow by conduction for a cylindrical body with an internal heat source, the nature of temperature distribution is
A. Linear
B. Hyperbolic
C. Parabolic
D. None of these
Question 222
Thermal conductivity of a conducting solid material depends upon its
A. Temperature
B. Porosity
C. Both A & B
D. Neither A nor B
Question 223
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
Question 224
Dropwise condensation of steam on cooling surface is promoted
A. An oily surface
B. When both the steam and the tube are clean
C. Only in presence of air
D. None of these
Question 225
Crystallisation of solids from a homogeneous solution is a/an __________ process.
A. Exothermic
B. Mildly endothermic
C. Highly endothermic
D. None of these
Question 226
Reynold's analogy states that (where, St = Stanton number f = friction factor)
A. St = f/2
B. St = f/4
C. St = 4f
D. St = f1/2
Question 227
Which is the most suitable for the concentration of foamy & frothy liquors?
A. Agitated film evaporator
B. Long tube vertical evaporator
C. Open pan evaporator
D. None of these
Question 228
Pick out the wrong statement.
A. In process heat exchangers, saturated steam is preferred over the superheated steam
B. The maximum is the emissive power of a surface at a temperature T₁ occurs at a wavelength of λ₁. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelengt
C. When a vertical plate is heated in infinite air environmental under natural convection conditions, the velocity profile in air, normal to the plate, exhibits a maximum
D. A body at 925 K emits an energy of 1.42 x 10¹¹σW/m² (σ is the Stefan-Boltzman constant) in the wavelength band between 3 μm to 4 μm. The fraction of this energy in the total energy emitted over
Question 229
Boiling point of a solution according to Duhring's rule is a linear function of the __________ of water.
A. Boiling point (at the same pressure)
B. Viscosity
C. Density
D. Thermal conductivity
Question 230
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
Question 231
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
Question 232
Which area is used in case of heat flow by conduction through a cylinder?
A. Logarithmic mean area
B. Arithmetic mean area
C. Geometric mean area
D. None of these
Question 233
__________ heat exchanger is used for chilling oil to be dewaxed.
A. U-tube
B. Double pipe
C. Fixed tube
D. Floating head
Question 234
For concentrating an aqueous solution of a material like anhydrous Na₂SO₄, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.
A. High pressure
B. Vacuum
C. Backward feed
D. None of these
Question 235
The purpose of providing a 'catchall' in the vapor line of an evaporator is to
A. Create vacuum
B. Regulate the vapor flow
C. Vent the non-condensible gases
D. Arrest the entrained liquid
Question 236
A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because
A. Total heat transfer area of all the effects is -less than that in a single effect evaporator system
B. Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
C. Boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system
D. Heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system
Question 237
A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
A. 555
B. 55.5
C. 0.55
D. 0.15
Question 238
A concentric double pipe heat exchanger as compared to the shell and tube heat exchanger for the same heat load requires
A. Less heating surface
B. More space
C. Lower maintenance cost
D. None of these
Question 239
Removal of __________ heat is involved in the condensation of a vapor under saturated conditions.
A. Super
B. Sensible
C. Latent
D. Both B & C
Question 240
A hot body will radiate heat most rapidly, if its surface is
A. White & rough
B. Black & rough
C. White & polished
D. Black & polished
Question 241
Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around __________ metres/second.
A. 1
B. 10
C. 20
D. 30
Question 242
At what value of Prandtl number, the hydrodynamic and thermal boundary layers are identical?
A. 0.5
B. 1
C. 1.5
D. 80
Question 243
Peclet number (Pe) is given by
A. Pe = Re.Pr
B. Pe = Re/Pr
C. Pe = Pr/Re
D. Pe = Nu.Re
Question 244
Pick out the correct equation.
A. JH = (St)(Pr)2/3 = f/2
B. JH = (St)(Pr)1/3 = f/2
C. JH = (St)2/3(Pr) = f/2
D. JH = (St)1/3(Pr) = f/2
Question 245
Kirchoff s law applies to __________ radiation.
A. Total
B. Monochromatic
C. Both A & B
D. Neither A nor B
Question 246
The purpose of providing bleed points in the evaporator is to
A. Admit the feed
B. Remove the product
C. Facilitate removal of non-condensable gases
D. Create vacuum
Question 247
Which of the following is unimportant in forced convection?
A. Reynolds number
B. Prandtl number
C. Grashhoff number
D. None of these
Question 248
Duhring rule is important in solving problems on
A. Distillation
B. Crystallisation
C. Evaporation
D. Humidification
Question 249
Fourier's law of heat conduction applies to __________ surfaces.
A. Isothermal
B. Non-isothermal
C. Both A and B
D. Neither A and B
Question 250
Fourier's law applies to the heat transfer by
A. Convection
B. Radiation
C. Conduction
D. All of the above
Question 251
Prandtl number is the ratio of
A. Momentum diffusivity to mass diffusivity
B. Momentum diffusivity to thermal diffusivity
C. Thermal diffusivity to mass diffusivity
D. Thermal diffusivity to momentum diffusivity
Question 252
Pick out the wrong statement.
A. Bubble size increases with the dynamic viscosity of the liquid in case of nucleate pool boiling
B. Thermal conductivity of a dry material is more than that of the damp material
C. Ratio of its capacity to economy equals the steam consumption in kg/hr in an evaporator
D. Vaporisation of organic substances in evaporator mostly causes foam formation
Question 253
Water is normally used as a coolant in the heat exchange equipments mainly because ofits
A. Abundance & high heat capacity
B. Low density
C. Low viscosity
D. High fluidity
Question 254
The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m².K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m².K. The overall heat transfer co-efficient at this time is
A. 1200W/m².K
B. 894W/m².K
C. 333W/m².K
D. 287 W/m².K
Question 255
Forced circulation evaporators are normally used for concentrating liquids having
A. Scaling characteristics
B. High viscosity
C. Both A & B
D. Neither A nor B
Question 256
A __________ evaporator employs an annular downtake.
A. Basket type
B. Horizontal
C. Long tube vertical
D. None of these
Question 257
During crystallisation, formation of crystal can occur in __________ solution only.
A. Saturated
B. Supersaturated
C. Undersaturated
D. All of the above
Question 258
Analogy between mass and heat transfer is not applicable in case of
A. Same velocity profile or equal eddy diffusivities
B. Thermal or pressure mass diffusion
C. Viscous heating or chemical reaction
D. Both B and C
Question 259
Heat transfer rate per unit area is called
A. Thermal conductivity
B. Heat flux
C. Heat transfer co-efficient
D. Thermal diffusivity
Question 260
In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
A. Concentrations
B. Chemical potentials
C. Activity co-efficients
D. Mass transfer co-efficients
Question 261
Heat flux is the time rate of heat transfer per unit
A. Length
B. Area
C. Volume
D. None of these
Question 262
Radiation heat transfer rates does not depend upon the
A. Type of absorbing surface
B. Distance between the heat source and the object receiving the heat
C. Surface area and temperature of the heat source
D. None of these
Question 263
A multiple effect evaporator as compared to a single effect evaporator of the same capacity has
A. Lower heat transfer area
B. Lower steam economy
C. Higher steam economy
D. Higher solute concentration in the product
Question 264
If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.
A. Hyperbolic
B. Parabolic
C. Linear
D. Logarithmic
Question 265
Nusselt number is the ratio of the temperature gradient at the wall to
A. Temperature difference
B. Heat flux
C. That across the entire pipe
D. None of these
Question 266
For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
A. Nu = 0.023 Re0.8 . Pr0.4
B. Nu = Gz
C. Nu = Gz
D. Nu = 2Gz0.5
Question 267
In case of a vertical tube evaporator, with increase in the liquor level, the
A. Capacity of the evaporator is decreased
B. Capacity of the evaporator is increased
C. True temperature drop increases
D. Both B and C
Question 268
For a perfectly transparent surface (like gases), the
A. Absorptivity = 0
B. Transmissivity = 1
C. Reflectivity = 0
D. All of the above
Question 269
The units of resistance to heat transfer is
A. J.m⁻².K⁻¹
B. J.m⁻¹.K⁻¹
C. W.m⁻².K⁻¹
D. W⁻¹m²K
Question 270
A sphere of radius 'R₁' is enclosed in a sphere of radius 'R₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is
A. 0
B. R₂/(R₁+R₂)
C. 1
D. (R₁/R₂)2
Question 271
For hot feed, forward feeding as compared to backward feeding results in __________ economy.
A. Increased
B. Decreased
C. No effect on
D. None of these
Question 272
A perfect black body is a perfect __________ of radiation.
A. Absorber
B. Emitter
C. Both A & B
D. Neither A nor B
Question 273
Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping
A. Both the tube sheets fixed
B. Both the tube sheets floating
C. The top tube sheet floating and bottom tube sheet fixed
D. The top tube sheet fixed and the bottom tube-sheet floating
Question 274
Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the
A. Maximum resistance in the series
B. Sum of all resistances
C. Average of all resistances
D. Minimum resistance presents in the series
Question 275
In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is
A. Infinity
B. Zero
C. Same as average heat transfer co-efficient for tube side
D. None of these
Question 276
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
Question 277
At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical?
A. 1
B. < 1
C. > 1
D. None of these
Question 278
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 tem
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
Question 279
A body is called grey if the monochromatic emissivity of the body is
A. Zero
B. Unity
C. Same for all wavelengths
D. Different for all wavelengths
Question 280
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
Question 281
Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law.
A. Stefan's
B. Dalton's
C. Wien's
D. Kirchoffs
Question 282
Stefan-Boltzman law applies to __________ body.
A. Black
B. White
C. Grey
D. Any colour
Question 283
__________ paint has the maximum absorption coefficient.
A. Black
B. Yellow
C. White
D. Grey
Question 284
A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun?
A. Yellow paint
B. White paint
C. Black paint
D. Grey paint
Question 285
The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emis-sivities εx & εy is given by
A. Εx + εy
B. Εx . εy
C. 1/εx + 1/εy
D. (εx + εy)/(εx + εy - εx . εy)
Question 286
Heat transfer co-efficient (h1) for liquids increases with
A. Increasing temperature
B. Decreasing temperature
C. Decreasing Reynolds number
D. None of these
Question 287
Baffle spacing
A. Is not the same as baffle pitch
B. Should be less than one fifth the diameter of the shell
C. Should be less than the inside diameter of the shell
D. None of these
Question 288
In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid.
A. Nucleate
B. Pool
C. Low pressure
D. None of these
Question 289
The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium. This is __________ law.
A. Kirchoffs
B. Planck's
C. Wien's displacement
D. Stefan-Boltzman
Question 290
Solid angle subtended by the finite surface at the radiating element is
A. Called the view factor
B. Called the angle of vision
C. Proportional to the square of the distance between surfaces
D. Expressed in terms of radians
Question 291
Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called
A. Radiation
B. Natural convection
C. Forced convection
D. Conduction
Question 292
Agitated film evaporator is suitable for concentrating __________ liquids.
A. Foaming
B. Viscous
C. Very thin
D. Corrosive
Question 293
Which of the following is not concerned with the heat transfer?
A. Brinkman number
B. Stanton number
C. Schmidt number
D. Peclet number
Question 294
1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m² and the overall heat transfer co-efficient to the liquid is 1500 W/m².°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°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
Question 295
A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?
A. Cube
B. Plate
C. Sphere
D. All of the above
Question 296
Choose the correct equation.
A. Nu = (Re) (Pr) (Gz)
B. Nu = (Re) (Pr) (St)
C. Nu = (Re)(Pr)
D. Nu = (Pr)(St)
Question 297
Fouling factor for a heat exchanger is given by (where, U₁ = heat transfer co-efficient of dirty surface U₂ = heat transfer co-efficient of clean surface)
A. U₁ - U₂
B. 1/U₁ - 1/U₂
C. 1/U₂ - 1/U₁
D. U₂ - U₁
Question 298
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
Question 299
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
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
Question 300
Film boiling is usually not desired in commercial equipments, because
A. The heat transfer rate is low in view of the large temperature drop
B. It is difficult to maintain
C. It is not economic
D. None of these
Question 301
Natural convection is characterised by
A. Grashhoff number
B. Peclet number
C. Reynolds number
D. Prandtl number
Question 302
Absorptivity and refletivity of a perfect black body are respectively
A. 1 and 0
B. 0 and 1
C. 1 and ?
D. 0 and 0.5
Question 303
Economy of a multiple effect evaporator depends upon the
A. Heat balance consideration
B. Rate of heat transfer
C. Both A and B
D. Neither A nor B
Question 304
In a forward feed multiple effect evaporator, the pressure is
A. Highest in last effect
B. Lowest in last effect
C. Same in all effects
D. Dependent on the number of effects
Question 305
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
Question 306
In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.
A. Geometric
B. Arithmetic
C. Logarithmic
D. Either A, B or C
Question 307
The most conducive surface for dropwise condensation to occur is the __________ surface.
A. Coated
B. Oily
C. Glazed & polished
D. Smooth
Question 308
The non-dimensional temperature gradient in a liquid at the wall of a pipe is the
A. Heat flux
B. Nusselt number
C. Prandtl number
D. Schmidt number
Question 309
Correction is applied to LMTD for __________ flow.
A. Parallel
B. Counter
C. Cross
D. None of these
Question 310
The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns.
A. 0.38-0.78
B. 0.5-50
C. 100-1000
D. 5-50
Question 311
A black body does not __________ radiation.
A. Absorb or emit
B. Refract
C. Reflect
D. Both B & C
Question 312
Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling?
A. Square pitch
B. Triangular pitch
C. Diagonal square pitch
D. None of these
Question 313
jH factor for heat transfer depends upon the __________ number.
A. Biot
B. Nusselt
C. Reynolds
D. Prandtl
Question 314
The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is
A. Nusselt number
B. Sherwood number
C. Schmidt number
D. Stanton number
Question 315
Duhring's plot' is of use in
A. Extractive distillation
B. Evaporation
C. Leaching
D. Absorption
Question 316
Heat exchangers operating, when the asymptotic range is reached,
A. Provide very large heat transfer co-efficient
B. Results in making part of the heating surface inactive
C. Results in abruptly increased velocity
D. None of these
Question 317
In natural convection heat transfer, the correlating parameter is the
A. Graetz number
B. Eckert number
C. Grashoff number
D. Bond number
Question 318
Stefen's block body radiation law can also be derived from __________ law.
A. Kirchoffs
B. Planck's
C. Fourier's
D. None of these
Question 319
What is the emissivity of a black body?
A. 1
B. 0
C. 0.9
D. 0.5
Question 320
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
Question 321
Unsteady state heat conduction occurs, when
A. Temperature distribution is independent of time
B. Temperature distribution is dependent on time
C. Heat flows in one direction only
D. Three dimensional heat flow is concerned
Question 322
To reduce the tube side pressure drop for the same flow rate, the heat exchanger recomended is
A. 1-2 heat exchanger
B. 1-1 heat exchanger
C. 3-2 heat exchanger
D. 2-4 heat exchanger
Question 323
In the free convection regime of pool boiling, the heat flux is proportional to
A. Δt1/2
B. Δt2
C. Δt5/4
D. Δt
Question 324
The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in lminar zone is related as
A. Ha = 0.8hL
B. Ha = 2hL
C. Ha = hL
D. Ha= 5hL
Question 325
For what value of Prandtl number, St = f/2?
A. 1.5
B. 1
C. > 1
D. < 1
Question 326
Prandtl and Reynolds analogy are same, when Prandtl number is
A. 0.5
B. 1
C. > 2
D. 1.5
Question 327
Calburn analogy is applicable for the value of Prandtl number from
A. 0.001 to 1
B. 0.6 to 120
C. 0.5 to 5
D. 120 to 400
Question 328
Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is
A. 0.1
B. >1
C. < 1
D. L
Question 329
Conductance is given by(where, x = thickness, A = heat flow area, K = thermal conductivity.)
A. X/KA
B. KA/x
C. K/Ax
D. A/Kx
Question 330
Baffles are provided in heat exchangers to increase the
A. Fouling factor
B. Heat transfer area
C. Heat transfer co-efficient
D. Heat transfer rate
Question 331
What is the geometric mean of two heat transfer areas A₁ and A₂ ?
A. √(A₁ . A₂)
B. √(A₁ + A₂)
C. 1/2 √(A₁ . A₂)
D. 2 √(A₁ . A₂)
Question 332
If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface tempeature follows __________ law.
A. Parabolic
B. Hyperbolic
C. Linear
D. Logarithmic
Question 333
In a single effect evaporator, the economy is
A. 1
B. < 1
C. > 1
D. None of these
Question 334
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
Question 335
Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is
A. Vertical heat exchanger with steam on tube side
B. Vertical heat exchanger with steam on shell side
C. Horizontal heat exchanger with steam on tube side
D. Horizontal heat exchanger with steam on shell side
Question 336
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
Question 337
Overall heat transfer co-efficient of a particular tube is U₁. If the same tube with some dirt deposited on either side has coefficient U₂, then
A. U₁ = U₂
B. U₂ > U₁
C. U₁ > U₂
D. U₁ = dirt factor - U₂
Question 338
If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is
A. 1
B. 2
C. 1-2
D. 4
Question 339
Temperature profile in steady state heat transfer is
A. Asymptotic
B. Hyperbolic
C. Parabolic
D. Linear
Question 340
The inner wall of a furnace is at a temperature of 700°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.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m⁻².°C-1. The rate of heat loss from the outer surface in W.m-2is
A. 165.4
B. 167.5
C. 172.5
D. 175
Question 341
In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid
A. Is inversely proportional to the resistance across which the drop occurs
B. And the wall are proportional to individual resistances
C. And the wall is not related
D. None of these
Question 342
Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of __________ °C.
A. 40
B. 95
C. 70
D. 50
Question 343
In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is
A. ∞
B. 0
C. Equal to the difference between hot and cold fluids inlet temperature
D. Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature
Question 344
When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
A. Pool
B. Nucleate
C. Transition
D. Film
Question 345
Boiling point elevation for a strong and concentrated solution is found by Duhring's rule, which states that at the same pressure, the boiling point of a solution is a linear function of the __________ of pure water.
A. Boiling point
B. Dynamic viscosity
C. Kinematic viscosity
D. Density
Question 346
The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.
A. Viscosity
B. Density
C. Thermal conductivity
D. Corrosive nature
Question 347
Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow. )
A. T
B. 1/ρ
C. 1/A
D. All of the above
Question 348
What is the steam economy in case of a single effect evaporator system?
A. 1
B. >1
C. < 1
D. 0.1
Question 349
Graetz number is given by
A. mCp/kL
B. kL/mCp
C. mCp/kμ
D. kμ/mCp
Question 350
Grashhoff number is given by
A. gD³.β.Δtρ²/μ²
B. gD2βΔtρ/μ²
C. gD2βΔtP²μ
D. gD³βΔtP²/μ
Question 351
In a shell and tube heat exchanger, square pitch compared to triangular pitch
A. Gives a higher shell side pressure drop
B. Gives a lower shell side pressure drop
C. Can pack more surface area into a shell of given diameter
D. None of these
Question 352
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
Question 353
An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is
A. 4000
B. 9000
C. 4600
D. 3000
Question 354
Use of transverse baffles in a shell and tube heat exchanger is done to increase the
A. Rate of heat transfer
B. Flow velocity
C. Turbulence of shell side fluid
D. All of the above
Question 355
Heat exchanger tubes are never made of
A. Plain carbon steel
B. Stainless steel
C. Lead
D. Copper
Question 356
Which of the following has the minimum absorptivity?
A. Aluminium foil
B. Coal dust
C. Refractory bricks
D. Iron plates
Question 357
The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is
A. Lower tube side pressure drop
B. Lower shell side pressure drop
C. Higher tube side heat transfer co-efficient
D. Higher shell side heat transfer co-efficient
Question 358
The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation.
A. Greater than
B. Lower than
C. Is same as
D. Half
Question 359
The purpose of providing expansion bellows in the shell of tubular exchanger is to
A. Increase the heating load
B. Impart structural strength
C. Account for the uneven expansion of shell and tube bundles
D. Facilitate increase of shell length, if needed
Question 360
The driving potential for the crystal growth during crystallisation is the __________ of the solution.
A. Concentration
B. Viscosity
C. Super-saturation
D. Density
Question 361
Nusselt number is the ratio of the
A. Temperature gradient of the wall to that across the entire pipe
B. Temperature difference to the temperature gradient at the wall
C. Heat flux at the wall to that across the entire pipe
D. None of these
Question 362
For what value of Prandtl number, the Col-burn analogy is valid?
A. 0.06 to 120
B. 0.6 to 120
C. 1 to 103
D. L to 50
Question 363
Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid?
A. Bleed point
B. Vent
C. Catchall
D. Baffle
Question 364
If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.
A. Increase
B. Decrease
C. Not affect
D. Increase the condensing film co-efficient as well as
Question 365
Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°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
Question 366
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
Question 367
The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
A. 1.66
B. 88.66
C. 3.66
D. Dependent on NRe only
Question 368
The statement that "maximum wavelength of radiation is inversly proportional to the temperature" is __________ law.
A. Stefan-Boltzman's
B. Planck's
C. Wien's displacement
D. None of these
Question 369
In forced circulation, the heating element is injected
A. Internally
B. Externally
C. Both A and B
D. Neither A nor B
Question 370
Log mean temperature difference (LMTD) cannot be used, if
A. Heat transfer co-efficient over the entire heat exchanger is not constant
B. There exists an unsteady state
C. The heat capacity is not constant and there is a phase change
D. None of these
Question 371
In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid
A. Varies directly as the area and the LMTD
B. Directly proportional to LMTD and inversely proportional to the area
C. Varies as square of the area
D. None of these
Question 372
Multiple effect evaporation is generally recommended, when the
A. Large scale evaporation of liquor is needed
B. Corrosive liquids are to be concentrated
C. Fuel is cheaply available
D. Evaporation on small scale is to be done
Question 373
For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of
A. 1
B. 1.74
C. 6.1
D. 37
Question 374
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
Question 375
A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is
A. 6000
B. 24000
C. 60000
D. 48000
Question 376
The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as
A. (ΔT)1/4
B. (ΔT)1/2
C. (ΔT)5/4
D. (ΔT)3/4
Question 377
Harmonic mean temperature difference is given by
A. √(ΔT₁ . ΔT₂)
B. 2.(ΔT₁ . ΔT₂)/(ΔT₁ + ΔT₂)
C. 2.(ΔT₁ . ΔT₂)(ΔT₁ - ΔT₂)
D. (ΔT₁ - ΔT₂)/(ΔT₁ . ΔT₂)
Question 378
The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m². The flux, when the element temperature is increased to 1000°C for the same furnace temperature is
A. 11.2 kW/m²
B. 12.0 kW/m²
C. 14.6 kW/m²
D. 16.5 kW/m²
Question 379
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 100°C and the inside heat transfer co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?
A. 35.5
B. 43.75
C. 81.25
D. 48.25
Question 380
Pick out the wrong statement.
A. Fluid movement under the influence of buoyant forces resulting from change in density takes place in case of natural convection
B. The ratio NNu/NRe . Npr is called the Stanton number
C. The Peclet number is a measure of the ratio of energy transport by convection to that by conduction
D. The Colbum jH factor for heat transfer is given by Nst Npr
Question 381
Radiation energy is emitted by all the substances, which are above
A. 0°K
B. 0°C
C. 100°C
D. Room temperature
Question 382
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
Question 383
Extremely large or small volumes of fluids are generally best routed through the shell side of a shell and tube heat exchanger, because of the
A. Less corrosion problems
B. Flexibility possible in the baffle arrangement
C. Low pressure drop
D. High heat transfer co-efficient
Question 384
Pick out the wrong statement.
A. The value of hydrostatic head increases with increase in vacuum in the effect in a multiple effect evaporator system
B. Entering velocity of the liquid in the tubes of natural circulation evaporators is in the range of 0.3 to 0.9 metre/second
C. Duhring's plot is used for calculating the concentration of solution
D. In a multiple effect evaporation system, the number of effects is limited by the total boiling point rise
Question 385
Thermal diffusivity of a material
A. Has the unit m² /sec
B. Is defined as K/ρ . Cp
C. Is the ratio of thermal conductivity to thermal capacity
D. All of the above
Question 386
(Cp . μ)/K is termed as the __________ number.
A. Grashoff
B. Nusselt
C. Prandtl
D. Stanton
Question 387
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the
A. Surrounding temperature
B. Average temperature of the fin
C. Temperature of the fin end
D. Constant temperature equal to that of the base
Question 388
Double pipe heat exchangers are preferably useful, when
A. High viscosity liquid is to be cooled
B. Requirement of heat transfer area is low
C. Overall heat transfer co-efficient is very high
D. A corrosive liquid is to be heated
Question 389
The thermal boundary layer at NPr > 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
Question 390
Maximum heat transfer rate is achieved in __________ flow.
A. Co-current
B. Counter-current
C. Turbulent
D. Laminar
Question 391
(NRe.NPr)(D/L) is called the __________ number
A. Peclet
B. Stanton
C. Graetz
D. None of these
Question 392
In a boiling curve, the peak heat flux is called the __________ point.
A. Nusselt
B. Leidenfrost
C. Boiling
D. Burnout
Question 393
Sensible heat of hot industrial flue gases can not be recovered by a/an
A. Economiser
B. Regenerator
C. Ceramic recuperator
D. None of these
Question 394
LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is
A. 0
B. 1
C. >1
D. <1
Question 395
Maximum heat transfer rate is obtained in __________ flow.
A. Laminar
B. Turbulent
C. Creeping
D. Transition region
Question 396
1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is
A. 520
B. 200
C. 400
D. 500
Question 397
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
Question 398
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 1200°K, then the temperature drop (in °K) across the layer of material 'A' is
A. 125
B. 133
C. 150
D. 160
Question 399
For a counter current heat exchanger with Tih = 80°C, T°c = 60°C, T°h = 50°C and Tic = 30°C, and the temperature difference between the two streams being the same everywhere along Z, the direction of flow of hot fluid. The temperature profile should satisfy
A. d²T/dZ² > 0
B. d²T/dZ² = 0
C. d²T/dZ² < 0
D. dT/dZ = 0
Question 400
Planck's distribution law is valid for __________ bodies.
A. Black
B. White
C. Coloured
D. All of the above
Question 401
Among liquids, water has a comparatively high value of thermal conductivity, due to its
A. Low density
B. High viscosity
C. Partial ionisation
D. Dense structure
Question 402
Corrosiveness of steam condensate is due to the presence of
A. CO₂
B. Dissolved O₂
C. Both A & B
D. Neither A nor B
Question 403
Evaporation by thermocompression results in the
A. Saving of steam
B. Realisation of multiple effect economy in a single effect
C. Both A and B
D. None of these
Question 404
An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporisation of another, is called a
A. Boiler
B. Heat exchanger
C. Recuperator
D. Regenerator
Question 405
Which of the following is directly concerned with the heat transfer?
A. Strouhal number
B. Sherwood number
C. Euler number
D. Grashoff number
Question 406
Small scale evaporation is done in a
A. Heat exchanger
B. Condenser
C. Multiple effect evaporator
D. Steam jacketed kettle
Question 407
Evaporator tubes are generally
A. Horizontal
B. Vertical
C. Inclined
D. Random
Question 408
The thickness of condensate layer in filmwise condensation depends on the
A. Condensation rate
B. Surface configuration
C. Liquid flow rate from the surface
D. All of the above
Question 409
Intermittant tube cleaning is possible to be done in case of a __________ evaporator.
A. Basket type
B. Horizontal tube
C. Calendria
D. None of these
Question 410
Boiling of milk in an open vessel is an example of __________ boiling.
A. Film
B. Sub-cooled
C. Saturated nucleate
D. None of these
Question 411
Steam is routed through the tube in case of a __________ evaporator.
A. Basket type
B. Horizontal tube
C. Short tube vertical
D. Long tube vertical
Question 412
The actual temperature drop across the heating surface of an evaporator depends on the
A. Liquid depth over the heating surface
B. Solution being evaporated
C. Pressure difference between the steam chest and the vapor space above the boiling liquid
D. All of the above
Question 413
In a shell and tube heat exchanger,
A. The temperature drops in the two fluids and the wall are proportional to individual resistances
B. The temperature drop is inversely proportional to the resistance across which the drop occurs
C. There is no relationship between temperature drop and resistance
D. The relationship is not generalised
Question 414
In Biot number, the characteristic length used is the ratio of the __________ of the solid.
A. Volume to surface area
B. Perimeter to surface area
C. Surface area to volume
D. Surface area to perimeter
Question 415
Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger?
A. Corrosiveness & fouling characteristics
B. Pressure
C. Viscosity
D. Density
Question 416
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
D. 1/CE
Question 417
Pick out the wrong statement.
A. Solvates' are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a 'hydrate'
B. In heat exchanger calculations (Δt)weighted is used in place of Δt, when it involves more than one sequence of heating or cooling i.e., desuperheating & condensation or condensation & sub-cooling
C. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted
D. In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area
Question 418
Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low
A. Hardness
B. Dissolved soilds content
C. Suspended solids content
D. All of the above
Question 419
Open pan evaporators are preferred to be used, when the solution to be concentrated is
A. Scaling
B. Highly viscous
C. Corrosive
D. Salty
Question 420
All analogy equations connecting friction factor and heat transfer co-efficient apply only to
A. Wall or skin friction
B. Form friction
C. Both A and B
D. Turbulent flow
Question 421
Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be
A. 0.35
B. 0.45
C. 0.55
D. 0.85
Question 422
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
Question 423
The main purpose of providing fins on heat transfer surface is to increase the
A. Temperature gradient
B. Mechanical strength of the equipment
C. Heat transfer area
D. Heat transfer co-efficient
Question 424
Steam trap is used to
A. Condense the steam flowing in the pipeline
B. Remove water resulting from partial condensation of steam
C. Stop the supply of steam
D. None of these
Question 425
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
Question 426
For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number)
A. NPr
B. NPr1/3
C. NPr-1
D. NPr-1/3
Question 427
The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the
A. Heating volume
B. Heat transfer area
C. Nusselt number
D. None of these
Question 428
The critical radius 'r' of insulation on a pipe is given by
A. r = 2k/h
B. r = k/h
C. r = k/2h
D. r = h/k
Question 429
Multiple effect evaporation accounts for
A. Steam economy
B. Lower operating costs
C. Investment economy
D. None of these
Question 430
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
Question 431
The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)
A. K/h0
B. 2K/h0
C. h0/K
D. h0/2K
Question 432
Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface?
A. Liquid density
B. Liquid viscosity
C. Hot surface temperature
D. Interfacial tension
Question 433
Finned tube heat exchangers
A. Give larger area per tube
B. Use metal fins of low thermal conductivity
C. Facilitate very large temperature drop through tube wall
D. Are used for smaller heat load
Question 434
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
Question 435
The sum of reflectivity and absorptivity for an opaque body is equal to
A. 0.5
B. 1
C. 0
D. 2
Question 436
The unit of conductance in SI unit is
A. W/m
B. W/m²
C. W/°K
D. W/m°K
Question 437
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)
Question 438
With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer
A. Decreases
B. Increases
C. Increases exponentially
D. Remains unaffected
Question 439
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
Question 440
Prandtl number for most of dry gases is about
A. 0.001
B. 0.72
C. 70
D. 150
Question 441
For a multipass shell and tube heat exchanger, the LMTD correction factor is always
A. 1
B. > 1
C. < 1
D. Between 1 & 2
Question 442
Which of the following is the most widely used heat insulating material for pipelines carrying steam?
A. Tar dolomite bricks followed by asbestos
B. Fireclay refractory followed by aluminium sheet
C. Cotton followed by aluminium foil
D. 85% magnesia cement and glass wool
Question 443
The energy radiated from a surface Q at absolute temperature T is related as
A. Q ∝ T²
B. Q ∝ T⁴
C. Q ∝ T³
D. None of these
Question 444
Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator?
A. Long vertical evaporator
B. Horizontal tube evaporator
C. Agitated film evaporator
D. Calenderia vertical tube evaporator
Question 445
Viscous & heat sensitive liquids are concentrated in __________ evaporators.
A. Open pan
B. Long tube
C. Agitated film
D. None of these
Question 446
Heat sensitive materials can be concentrated in an evaporator employing
A. Vacuum
B. High pressure
C. High residence time
D. None of these
Question 447
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
Question 448
The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body)
A. αT
B. α 1/T
C. α T⁴
D. Independent of T
Question 449
In SI units, fouling factor is expressed in
A. m²°K/W
B. W/m²°K
C. m²°K
D. m°K/W
Question 450
In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid.
A. Equal to
B. More than
C. Less than
D. Either more or less than (depending upon the fluid)
Question 451
Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.
A. Grashoff
B. Reynolds
C. Both A & B
D. Prandtl & Grashoff
Question 452
A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB 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. CPA > CPB
B. CPA < CPB
C. KA < 0.5kB
D. KA>2 kB
Question 453
In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m².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 m²/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
Question 454
In pipe flow, heat is transferred from hot wall to the liquid by
A. Conduction only
B. Forced convection only
C. Forced convection and conduction
D. Free and forced convection
Question 455
In which mode of heat transfer, the Biot number is important?
A. Transient heat conduction
B. Natural convection
C. Forced convection
D. Radiation
Question 456
Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by
A. Eddies current
B. Conduction
C. Convection
D. None of these
Question 457
In a cooling tower, water becomes cool by
A. Loosing sensible heat
B. Heat transfer to surroundings
C. Vaporisation due to heat loss to air
D. Loosing latent heat
Question 458
Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m²°C.
A. 10-50
B. 100-500
C. 1000-1500
D. 5000-15000
Question 459
LMTD for counterflow and prallel flow heat exchanger will be the same, when the
A. Cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)
B. Outlent temperature of both the hot and cold fluid are same
C. Outlet temperature of hot fluid is less than the outlet temperature of the cold fluid
D. None of these
Question 460
In a shell and tube heat exchanger, floating head is used for
A. Large temperature differentials
B. High heat transfer co-efficient
C. Low pressure drop
D. Less corrosion of tubes
Question 461
When warm and cold liquids are mixed, the heat transfer is mainly by
A. Conduction
B. Convection
C. Radiation
D. Both A & C
Question 462
For evaporation of viscous solution in a multiple effect evaporator, the prefered feeding scheme is
A. Forward
B. Backward
C. Parallel
D. None of these
Question 463
Pick out the wrong statement:
A. With change in temperature, the radiant energy emitted by a black body remains unchanged
B. Absorptivity of a body approaches unity in case of diffuse reflection
C. Absorptivity of a perfectly black body is unity
D. Value of Stefan-Boltzman constant is 4.876 x 10⁻⁸ KCal/m².hr.°K⁴
Question 464
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
Question 465
The steam ejector is used to
A. Remove condensate from the steam pipelines
B. Create vacuum
C. Superheat the steam
D. None of these
Question 466
Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is
A. 1
B. < 1
C. > 1
D. > 5
Question 467
Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is
A. 0.2
B. 0.4
C. 0.6
D. 0.8
Question 468
For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally
A. Decreases
B. Increases
C. Remains unchanged
D. Increases exponentially
Question 469
In a single evaporator system, the steam economy __________ by creating vacuum in the evaporator.
A. Increases
B. Decreases
C. Remains constant
D. May increase or decrease, depends on the vacuum
Question 470
One kilogram of water at 0°C is changed to superheated steam of one atm pressure and 300° C. The major heat consumption in the process will be to
A. Heat the water from 0°C to 100°C
B. Evaporate the water
C. To superheat the steam
D. Data insufficient, can
Question 471
jH factor for heat transfer is not a function of the __________ number.
A. Reynolds
B. Nusselt
C. Grashoff
D. Both B & C
Question 472
Nusselt number (for forced convection heat transfer) is a function of the __________ number.
A. Prandtl
B. Reynolds
C. Both A & B
D. Neither A nor B
Question 473
Prandtl number is the reciprocal of
A. Thermal diffusivity/Momentum diffusivity
B. Thermal diffusivity x Momentum
C. Thermal diffusivity x Mass diffusivity
D. Mass diffusivity x Momentum diffusivity
Question 474
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
Question 475
With increase in temperature, the total emissivity of conductors
A. Increases
B. Decreases
C. Remains same
D. Decreases linearly
Question 476
For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and pressure drop are
A. Same
B. Different
C. Never different
D. Linearly related
Question 477
Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid
A. For fluids in laminar flow
B. For fluids in tubulent flow
C. When Grashhoff number is very important
D. For liquid metals
Question 478
The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid
A. Its evaporation loss
B. Excessive corrosion
C. Uneconomic LMTD
D. Decrease in heat exchanger efficiency
Question 479
The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K₀ + at. where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be
A. W/m.k
B. W/m
C. W/m.k²
D. None, A is just a number
Question 480
The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8.
A. 20.8
B. 40.8
C. 40.4
D. 20.4
Question 481
Electromagnetic radiations propagate in vacuum with a velocity of __________ metre/second.
A. 3 x l05
B. 3 x l08
C. 3 x l010
D. 3 x l012
Question 482
Which of the following is generally considered as opaque surface towards radiations?
A. Gases
B. Solids
C. Liquids
D. Both B and C
Question 483
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
Question 484
Heat transfer by __________ may not necessarily require the presence of a medium.
A. Conduction
B. Natural convection
C. Forced convection
D. Radiation
Question 485
Film condensation is promoted on a/an __________ surface.
A. Oily
B. Coated
C. Clean & smooth
D. Dirty
Question 486
Dropwise condensation is promoted on a/an __________ surface.
A. Glazed
B. Oily
C. Coated
D. Smooth
Question 487
In a backward feed multiple effect evaporator
A. Feed is introduced in the first effect
B. Feed flows from low pressure to high pressure
C. No pumps are required between successive effects
D. None of these
Question 488
Which type of heat exchanger is preferred for heavy heat loads?
A. Double pipe
B. Plate fine
C. Series and parallel set of shell and tube
D. None of these
Question 489
A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°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
Question 490
Boiling point elevation of an ideal solution
A. Increases rapidly with temperature rise
B. Decreases rapidly with temperature rise
C. In independent of pressure
D. Both B and C
Question 491
The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is
A. 2
B. 1-2
C. 4
D. 1-4
Question 492
200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10⁻³ kg/m².s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m²/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)
A. 0.5
B. 0.05
C. 0.1
D. 0.15
Question 493
It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is
A. 3.06 x l0⁵
B. 6.12 x 10⁵
C. 7.24 x 10⁵
D. 9.08 x 10⁵
Question 494
Fqra cold viscous feed, backward feed gives __________ than forward feed.
A. A higher capacity
B. A lower capacity
C. Lower economy
D. None of these
Question 495
In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to __________ the velocity head.
A. Twice
B. Four times
C. Square root of
D. Square of
Question 496
Terminal point temperature differences between fluids in case of a heat exchanger is termed as
A. Approach
B. Log mean temperature difference
C. Arithmetic mean temperature difference
D. Geometric mean temperature difference
Question 497
For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is
A. 3
B. 0.33
C. 1
D. 1.33
Question 498
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
Question 499
Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )
A. t⁴
B. T⁴
C. 1/t⁴
D. 1/T⁴
Question 500
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
Question 501
The film co-efficient between condensing vapour and metal wall increases with
A. Increasing temperature of the vapour
B. Decreasing temperature of the vapour
C. Increasing viscosity of the film of condensate
D. Increasing temperature drop
Question 502
The main function of baffles provided in a shell and tube heat exchanger is to
A. Facilitate the cleaning of outer tube surface
B. Enhance turbulence
C. Hold the tubes in position
D. All of the above
Question 503
The maximum heat transfer co-efficient from steam heating will be attained when the steam is
A. Supersaturated
B. Saturated
C. Wet
D. None of these
Question 504
The rate of emission of radiation by a body does not depend upon the
A. Wavelength of radiation
B. Surface temperature of the body
C. Nature of the surface
D. Shape and porosity of the body
Question 505
In a multiple effect evaporator, the effect of boiling point elevation is to
A. Reduce the capacity
B. Reduce the economy
C. Increase the economy
D. None of these
Question 506
Which of the following is concerned with both heat and mass transfer?
A. Lewis relationship
B. Nusselt number
C. Kutateladze number
D. Froude number
Question 507
The ratio of kinematic viscosity to thermal diffusivity is called the __________ number.
A. Peclet
B. Prandtl
C. Stanton
D. Nusselt
Question 508
(NGr x NPr) is called the __________ number.
A. Graetz
B. Reyleigh
C. Nusselt
D. Stanton
Question 509
h.D/K is called the __________ number.
A. Nusselt
B. Peclet
C. Rayleigh
D. Grashoff
Question 510
A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter 'd'. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to
A. D0.8
B. D-0.2
C. D-1
D. D-1.8
Question 511
The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m². The approximate surface temperature (K) is (Stefan-Boltzman constant = 5.67xl0⁻⁸ W/m².K⁴)
A. 1000
B. 727
C. 800
D. 1200
Question 512
Crystal size in a continuous crystalliser depends upon the
A. Rate of heat transfer
B. Degree of turbulence
C. Degree of supersaturation
D. All of the above
Question 513
For heat flow through very thick walled cylinder, use____mean radius.
A. Arithmetic
B. Logarithmic
C. Geometric
D. Either A or C
Question 514
In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell)
A. 0.25 D
B. 0.75 D
C. 0.50 D
D. None of these
Question 515
Tube pitch is the __________ of tube diameters and the clearances.
A. Sum
B. Difference
C. Ratio
D. None of these
Question 516
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
Question 517
Multiple effect evaporators ar used to
A. Increase the steam economy & decrease the capacity
B. Increase the steam economy & the capacity
C. Decrease the steam economy & the capacity
D. Decrease the steam economy & increase the capacity
Question 518
Pick out the wrong statement.
A. The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation
B. Film co-efficient for vaporisation decreases as a result of vapor binding
C. In industrial practice, sub-cooling of condensate is required, when the condensate is a volatile liquid and is to be transferred for storage
D. Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher
Question 519
Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because
A. Convection becomes important
B. Conduction becomes important
C. Radiation becomes important
D. Sub-cooled boiling occurs
Question 520
For a laminar flow of fluid in a circular tube, 'h₁' is the convective heat transfer co-efficient at velocity 'V₁'. 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 h₁
B. 0.794 h₁
C. 0.574 h₁
D. 1.741 h₁
Question 521
If h₁ = inner film co-efficient and /h₂ = outer film co-efficient, then the overall heat transfer co-efficient is
A. Always less than h₁
B. Always between h₁ and h₂
C. Always higher than h₂
D. Dependent on metal resistance
Question 522
The unit of heat transfer co-efficient is
A. BTU/hr. ft²°F
B. BTU/hr. °F. ft
C. BTU/hr. °F
D. BTU/hr. ft
Question 523
If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length
A. Ha = hl
B. Ha = 2hl
C. Ha = 0.5 hl
D. Ha = 0.75 hl
Question 524
At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the
A. Buffer zone
B. Turbulent core
C. Both A and B
D. Viscous sub-layer
Question 525
Which is the most suitable for the con-certration of highly concentrated solution?
A. Open pan evaporation
B. Long tube vertical evaporator
C. Agitated film evaporator
D. None of these
Question 526
View factor is important in heat transfer by
A. Steady state conduction
B. Natural convection
C. Forced convection
D. Radiation
Question 527
Thermal diffusivity is the most important in heat transfer by
A. Conduction
B. Radiation
C. Condensation
D. Natural convection
Question 528
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
Question 529
In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell)
A. D/5 and D
B. D/2 and 2 D
C. D/4 and 2 D
D. D and 2 D
Question 530
Mode of heat transfer involved in the cooling of air cooled internal combustion engine is
A. Conduction
B. Natural convection
C. Forced convection
D. None of these
Question 531
Pick out the wrong statement.
A. By increasing the number of shell passes, the temperature cross in a shell and tube heat exchanger can be prevented
B. An underdesigned steam trap will back up the condensate instead of discharging it out
C. Steam condensate is corrosive because of the presence of dissolved oxygen in it
D. Film boiling is desirable in commercial equipments due to high heat transfer rate at low temperature drop
Question 532
Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re0.8 . Prn, 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
Question 533
LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counterflow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow.
A. Parallel
B. Mixed
C. Counterflow
D. Same in either A, B or C
Question 534
In evaporators, lowering the feed temperature
A. Increases the heating area required
B. Reduces the economy
C. Both A and B
D. Decreases the heating area required
Question 535
Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may be around __________ BTU.
A. 180
B. 970
C. 3.97
D. None of these
Question 536
Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212°F may be around __________ BTU.
A. 180
B. 970
C. 3.97
D. Data insufficient, can
Question 537
When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is
A. Free convection
B. Entry length problem in laminar forced conduction (developing thermal boundary layer)
C. Mixed convection (both free and forced)
D. Forced convection
Question 538
What is the thermal conductivity of a perfect heat insulator?
A. Zero
B. One
C. ∞
D. Between 0 and ∞
Question 539
Heat transfer by radiation between two bodies at T₁ & T₂ and in an ambient temperature of Ta°C depends on
A. T₁ - T₂
B. T₁ - Ta
C. T₂ - Ta
D. None of these
Question 540
Which of the following is correct?
A. Rate = Driving force x Resistance
B. Driving force = Rate x Resistance
C. Resistance = Driving force x Rate
D. Rate = Resistance/Driving force
Question 541
Double pipe heat exchangers are used
A. When heat transfer area required is very high
B. When heat transfer area required is very low, i.e (100-200 ft²)
C. Because it occupies less floor area
D. Because it is less costly
Question 542
Loss of heat from untagged steam pipe to the ambient air is by
A. Conduction
B. Convection
C. Radiation
D. All of the above
Question 543
A hot liquid is kept in a big room. The logorithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an
A. Ellipse
B. Straight line
C. Parabola
D. Circular arc
Question 544
Pick out the wrong statement.
A. Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient
B. In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles
C. S.I. unit of fouling factor is Watt/m².°K
D. Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube
Question 545
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