htn 1 Flashcards by Marie Cruz

Crystal size in a continuous crystalliser depends upon the
A. rate of heat transfer.
B. degree of turbulence.
C. degree of supersaturation.
D. all (a), (b) and (c).

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

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Air is best heated with steam in a heat exchanger of
A. plate type.
B. double pipe type with fin on steam side.
C. double pipe type with fin on air side.
D. shell and tube type.

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Which of the following is generally considered as opaque
surface towards radiations?
A. Gases
B. Solids
C. Liquids
D. Both (b) and (c)

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Black liquor generated during paper manufacture is
concentrated in a
A. single effect evaporator.
B. single effect evaporator followed by a crystalliser.
C. multiple effect evaporator.
D. multiple effect evaporators followed by a crystalliser.

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When vaporisation takes place directly at the heating surface, it
is called
A. film boiling
B. nucleate boiling
C. vapour binding
D. none of these

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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

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Reynold’s analogy states that
A. Nst α f
B. Nst α NRe
C. NNu α f
D. NRe α f

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

A. decreases
B. increases
C. remains constant
D. first decreases up to certain temp. & then increases

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Fourier’s law applies to the heat transfer by
A. convection
B. radiation
C. conduction
D. all (a), (b) & (c)

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For an ideal black body
A. absorptivity = 1
B. reflectivity = 1
C. emissivity = 0
D. transmissivity = 1

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Shell side pressure drop in a shell and tube heat exchanger does
not depend upon the
A. baffle spacing & shell diameter.
B. tube diameter & pitch.
C. viscosity, density & mass velocity of shell side fluid.
D. none of these.

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In the equation Q = UAΔt; Δt
A. geometric mean temperature difference.
B. arithmetic mean temperature difference.
C. logarithmic mean temperature difference.
D. the difference of average bulk temperatures of hot
and cold fluids.

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

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In Joule’s experiment, an insulated container contains 20 kg of
water initially at 25°C. It is stirred by an agitator, which is made
to turn by a slowly falling body weighing 40 kg through a height
of 4 m. The process is repeated 500 times. The acceleration due
to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator,
the temperature of water (in °C) is
A. 40.5
B. 34.4
C. 26.8
D. 25

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

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

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

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For shell and tube heat exchanger, with increasing heat transfer
area, the purchased cost per unit heat transfer area
A. increases
B. decreases
C. remains constant
D. passes through a maxima

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Presence of a non-condensing gas in a condensing vapour
A. increases the rate of condensation.
B. decreases thermal resistance.
C. is desirable to increase the film co-efficient.
D. none of these.

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Kirchoff s law applies to __________ radiation.
A. total
B. monochromatic
C. both (a) & (b)
D. neither (a) nor (b)

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The thermal efficiency of a reversible heat engine operating
between two given thermal reservoirs is 0.4. The device is used
either as a refrigerator or as a heat pump between the same
reservoirs. Then the coefficient of performance as a refrigerator
(COP)R and the co-efficient of performance as a heat pump
(COP)HP are
A. (COP)R = (COP)HP = 0.6
B. (COP)R = 2.5; (COP)HP = 1.5
C. (COP)R = 1.5; (COP)HP = 2.5
D. (COP)R = (COP)HP = 2.5

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Hot water (0.01 m3 /min) enters the tube side of a counter
current shell and tube heat exchanger at 80°C and leaves at
50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific
heat of 2 kJ/kg.K enters at 20°C. The log mean temperature
difference in °C is approximately
A. 32
B. 37
C. 45
D. 50

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In a heat exchanger, floating head is provided to
A. facilitate cleaning of the exchanger.
B. increase the heat transfer area.
C. relieve stresses caused by thermal expansion.
D. increase log mean temperature gradient.

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

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

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Heat produced when a steady state current, I passes through an
electrical conductor having resistance, ‘R’ is
A. IR
B. I^2R
C. IR^2
D. I^2R^2

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

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Convective heat transfer co-efficient in case of fluid flowing in
tubes is not affected by the tube length/diameter ratio, if the flow
is in the __________ zone.
A. laminar
B. transition
C. both ‘a’ & ‘b’
D. highly turbulent

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The actual temperature drop across the heating surface in an
evaporator depends on the
A. feed.
B. depth of liquid over heating surface.
C. pressure difference between steam chest and
vapour space.
D. all (a), (b) and (c).

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

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With the increase of temperature, the Col-burn jH factor
A. increases.
B. decreases.
C. remains unchanged.
D. may increase or decrease ; depending on
temperature.

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In case of evaporators, liquid entrainment results primarily due
to
A. high vacuum in the evaporator.
B. high evaporation rate.
C. foaming of the solution.
D. high heat transfer rate.

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

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

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The unit of heat transfer co-efficient in SI unit is
A. J/M2°K
B. W/m2°K
C. W/m°K
D. J/m°K

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Pick out the wrong statement.
A. In case of heat transfer by purely forced
convection, GR/Re
2 ≤ 1.

B. The equivalent diameter of heat transfer for a duct
of square cross-section (having each side as ‘x’) is
equal to 4x.
C. Distillation process is not the same as evaporation.
D. The effectiveness of nucleate boiling depends
basically on the ease with which the bubbles are
formed and detached from the heating surface.

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

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

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The number of kg vaporised per kg of steam fed to the
evaporator is defined as
A. capacity
B. rate of evaporation
C. economy
D. rate of vaporisation

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The equivalent diameter for pressure drop is __________ that
for heat transfer.
A. smaller than
B. greater than
C. equal to
D. not related with

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Controlling heat transfer film co-efficient is the one, which offers
__________ resistance to heat transfer.
A. no
B. the least
C. the largest
D. lower

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The heat flux (from outside to inside) across an insulating wall
with thermal conductivity, K= 0.04 W/m.°K and thickness 0.16m
is 10 W/m2. The temperature of the inside wall is - 5°C. The
outside wall temperature is
A. 25°C
B. 30°C
C. 35°C
D. 40°C

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Thermal conductivity of a conducting solid material depends
upon its
A. temperature
B. porosity
C. both (a) & (b)
D. neither (a) nor (b)

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

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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’

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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. √��
C. (ΔT)
1/4
D. (ΔT)
3/2

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Bulk of the convective heat transfer resistance from a hot tube
surface to the fluid flowing in it, is
A. in the central core of the fluid.
B. uniformly distributed throughout the fluid.
C. mainly confined to a thin film of fluid near the
surface.
D. none of these.

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Which of the following is concerned with both heat and mass
transfer?
A. Lewis relationship
B. Nusselt number
C. Kutateladze number
D. Froude number

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A backward feed multiple effect evaporator is better than forward
feed for concentrating cold feed, because it provides
A. higher economy
B. lower capacity
C. both (a) & (b)
D. lower economy

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

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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

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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.

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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.

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The absorptivity of a grey body at a given temperature
__________ with increasing wavelength of radiation.
A. increases
B. decreases
C. remains constant
D. may increase or decrease ; depends on the material

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Which one gives the monochromatic emissive power for black
body radiation?
A. Planck’s law
B. Kirchhoffs law
C. Wien’s law
D. Stefan-Boltzman law

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For what value of Prandtl number, St = f/2?
A. 1.5
B. 1
C. > 1
D. < 1

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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.

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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.

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The equation, nst=f/2/ 1+5(Npr-1)..
, corresponds to __ analogy.

A. Von-Karmann
B. Reynolds
C. Colburn
D. Prandtl

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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 (a), (b) and (c).

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Out of the following four assumptions used in the derivation of the equation for LMTD, which one is subject
to the largest deviation in practice?
A. Constant overall heat transfer co-efficient.
B. Constant rate of fluid flow.
C. Constant specific heat.
D. No partial phase change in the system.

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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

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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

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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 (a), (b) & (c)

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Temperature profile in steady state heat transfer is
A. asymptotic
B. hyperbolic
C. parabolic
D. linear.

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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.

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When vaporisation takes place through a blanketting film of gas,
the phenomenon is termed as __________ boiling.
A. pool
B. nucleate
C. transition
D. film

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Minimum recommended baffle spacing in a shell and tube heat
exchanger is about (where, D = shell diameter)
A. 0.2 D
B. 0.5 D
C. 0.66 D
D. 0.80 D

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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. t
4
B. T4
C. 1/t
4
D. 1/T4

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The Nusselt number for fully developed (both thermally and
hydrodynamically) laminar flow through a circular pipe, where
the wall heat flux is constant, is
A. 2.36
B. 4.36
C. 120.36
D. dependent on NRe only

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What is the unit of thermal conductivity?
A. Kcal/hr. m2 °C
B. Kcal/hr.m.°C
C. Kcal/hr.m
D. Kcal/hr. °C

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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

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In forced convection, the heat transfer depends on
A. Re, Pr
B. Re, Gr
C. mainly Gr
D. Re only

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In forced convection, the heat transfer depends on
A. Re, Pr
B. Re, Gr
C. mainly Gr
D. Re only

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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.

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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

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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

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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 (a), (b) and (c).

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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 (a), (b) and (c).

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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)

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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)

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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)

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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.

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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.

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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

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

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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.

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In a shell and tube type heat exchanger, the floating tube bundle
heat arrangement is used
A. in low range of temperature differences.
B. in high range of temperature differences.
C. because of its low cost.
D. to prevent corrosion of the tube bundles.

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Stefan-Boltzman law applies to __________ body.
A. black
B. white
C. grey
D. any colour

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The film co-efficient is decreased due to the presence of non
condensing gases in the vapors. The film co-efficient of
superheated vapor as compared to that of saturated vapor is
A. more
B. less
C. some
D. either more or less ; depends on the nature of
vapo

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A perfect black body is a perfect __________ of radiation.
A. absorber
B. emitter
C. both (a) & (b)
D. neither (a) nor (b)

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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)

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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

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Which of the following is directly concerned with the heat
transfer?
A. Strouhal number
B. Sherwood number
C. Euler number
D. Grashoff number

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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
8KCal/m2.hr.°K4

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Planck’s distribution law is valid for __________ bodies.
A. black
B. white
C. coloured
D. all (a), (b) & (c)

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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

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Radiation energy is emitted by all the substances, which are
above
A. 0°K
B. 0°C
C. 100°C
D. room temperature

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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/EX+ 1/EY
D.EX+EY/EX+EY - EX*EY

∙

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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

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What is the steam economy in case of a single effect evaporator
system?
A. 1
B. >1
C. < 1
D. 0.1

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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

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jH factor for heat transfer is not a function of the __________
number.
A. Reynolds
B. Nusselt
C. Grashoff
D. both (b) & (c)

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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

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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

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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

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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).

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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

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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

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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.

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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. ∞

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With increase in temperature, the thermal conductivity of steel
A. increases
B. decreases
C. remains unchanged
D. increases exponentially

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Which of the following forced convection heat transfer equation
accounts for the liquid viscosity effect for viscous liquids?
A. Dittus-Boeltier equation
B. Sieder-Tate equation
C. Nusselt equation
D. None of these

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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 ‘a’, ‘b’ & ‘c’.

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

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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

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Which of the following is not concerned with the heat transfer?
A. Brinkman number
B. Stanton number
C. Schmidt number
D. Peclet number

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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

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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.

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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

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Crystallisation of solids from a homogeneous solution is a/an
__________ process.
A. exothermic
B. mildly endothermic
C. highly endothermic
D. none of these

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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

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Value of Prandtl number for water ranges from
A. l to 2
B. 5 to 10
C. 100 to 500
D. 1000 to 2000

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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

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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

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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 = f^1/2

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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

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The sum of reflectivity and absorptivity for an opaque body is
equal to
A. 0.5
B. 1
C. 0
D. 2

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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

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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

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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’

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Heat transfer co-efficient (h1) for liquids increases with
A. increasing temperature.
B. decreasing temperature.
C. decreasing Reynolds number.
D. none of these.

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A diathermaneous substance __________ the thermal radiation
completely.
A. absorbs
B. reflects
C. transmits
D. none of these

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A hot body will radiate heat most rapidly, if its surface is
A. white & rough
B. black & rough
C. white & polished
D. black & polished

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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

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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

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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).

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A __________ surface has the maximum thermal emissivity out
of the following.
A. black & smooth
B. black & rough
C. white & smooth
D. white & rough

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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. d^2
D. d^1.5

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Mechanical recompression evaporation is used in the production
of
A. alcohol
B. distilled water
C. salt
D. fruits jam

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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

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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

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What is the thermal conductivity of a perfect heat insulator?
A. zero
B. one
C. ∞
D. between 0 and ∞

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‘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.

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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. d^0.8
B. d^-0.2
C. d^-1
D. d^-1.8

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Prandtl and Reynolds analogy are same, when Prandtl number
is
A. 0.5
B. 1
C. > 2
D. 1.5

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Heat transfer occurs by natural convection because change in
temperature causes difference in
A. viscosity
B. density
C. thermal conductivity
D. heat capacity

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The ratio of kinematic viscosity to thermal diffusivity is called the
__________ number.
A. Peclet
B. Prandtl
C. Stanton
D. Nusselt

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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

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________ paint has the maximum absorption coefficient.
A. Black
B. Yellow
C. White
D. Grey

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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.

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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.

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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.

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What is Nusselt number?
A. Cp u/ k
B. hD/k
C. h Cp/ u
D. Cp u /h

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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.

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The Dietus-Boelter equation for convective heat transfer (i.e.,
ℎ=0.023 K/D 𝑅𝑒^0.8𝑃𝑟^0.4 ) cannot be used for
A. low Reynold’s number
B. very low Grashoff number
C. molten metals
D. all (a), (b) and (c)

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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

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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

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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

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Film condensation is promoted on a/an __________ surface.
A. oily
B. coated
C. clean & smooth
D. dirty

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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

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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.

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Heat transfer rate per unit area is called
A. thermal conductivity
B. heat flux
C. heat transfer co-efficient
D. thermal diffusivity

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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.

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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

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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

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

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

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.

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

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

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

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

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.

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

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 (a), (b) and (c).

Multiple effect evaporators are commonly used in the
manufacture of P. Paper Q. Superphosphate
R. Sugar S. Fats
A. P and Q
B. P and R
C. P and S
D. R and S

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.

Which of the following has the highest thermal conductivity?
A. Brick
B. Air
C. Water
D. Silver

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

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

The rate of heat transfer through a pipe wall is given by,
q=2piK(Ti-To)/ln (Ri/Ro)
For cylinder of very thin wall, q can be approximated by
A. q= 2piK(Ti-To)/2 /ln (Ri/Ro)
B. q= 2piriK(Ti-To)/ Ro-Ri
C.q= 2piK(Ti-To)/ Ro-Ri
D. q= 2piK(Ti-To)/ (Ro-Ri)/2

Dropwise condensation occurs on __________ surfaces.
A. clean and dirt free
B. smooth clean
C. contaminated cooling
D. polished

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

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.

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)

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

Heat flux is the time rate of heat transfer per unit
A. length
B. area
C. volume
D. none of these

Film boiling occurs at __________ pressure.
A. atmospheric
B. sub-atmospheric
C. negative
D. very high

Heat flux through several resistances in series in analogous to
the current flowing through several
A. resistances in parallel.
B. capacitors in series.
C. resistances in series.
D. none of these.

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

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.

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.

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)

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.

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

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 ‘L’,
thermal conductivity ‘k’ and heat flow area ‘A’ is kL/A.
D. none of these.

In forced convection, the Nusselt number is a function of
A. Re and Pr
B. Re and Gr
C. Pr and Gr
D. Re and Sc

While the total emissivity of a perfect black body is unity, the
same for a real body is
A. 0
B. 1
C. > 1
D. between 0 and 1

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.

According to Reynolds analogy, Stanton number is equal to
(where, f = Fanning friction factor)
A. 2f
B. f
C. f/2
D. f/4

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.

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

In thermal radiation for a black body (where, ε is emissivity and
α is absorptivity)
A. α = 1; ε ≠ 1
B. α ≠ 1, ε = 1
C. α ≠ 1, ε ≠ 1
D. α = 1; ε = 1

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.

When warm and cold liquids are mixed, the heat transfer is
mainly by
A. conduction
B. convection
C. radiation
D. both(a) & (c)

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 will cool at the same rate

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.

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.

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

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

At what value of Prandtl number, the hydrodynamic and thermal
boundary layers are identical?
A. 0.5
B. 1
C. 1.5
D. 80

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.

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.

Trap is used to remove __________ from steam pipe lines.
A. steam
B. condensate
C. non-condensables
D. none of these

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

Tube pitch is the __________ of tube diameters and the
clearances.
A. sum
B. difference
C. ratio
D. none of these

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

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

Natural convection is characterised by
A. Grashhoff number
B. Peclet number
C. Reynolds number
D. Prandtl number

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

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

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

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)

A body is called grey if the monochromatic emissivity of body is
A. zero
B. unity
C. same for all wavelengths
D. different for all wavelengths

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.

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

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.

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.

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

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.

Graetz number is given by
A. mCP/kL
B. kL/mCp
C. mCp/ku
D. kL/mCp

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

Economy of an evaporator is influenced by the
A. steam pressure
B. feed temperature
C. number of effect
D. both(b) & (c)

For a perfectly transparent surface (like gases), the
A. absorptivity = 0
B. transmissivity = 1
C. reflectivity = 0
D. all (a), (b) & (c)

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

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

In regenerative air preheater (as practised in heating of coke
ovens), the heat is transferred
A. through a metallic wall.
B. by direct contact of hot flue gas with air.
C. by heating an intermediate material (like chequor
bricks) and then heating the air from this hot material.
D. none of these.

__________ equation relates the thermal conductivity of a solid
to its temperature.
A. Antonie
B. Kopp’s
C. Lee’s
D. Kistyakowski

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

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.

Viscous & heat sensitive liq. are concentrated in __ evaporators.
A. open pan
B. long tube
C. agitated film
D. none of these

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

The ratio of momentum diffusivity to thermal diffusivity is the
______ number.
A. Prandtl
B. Nusselt
C. Stanton
D. Grashoff

Maximum heat transfer rate is obtained in __________ flow.
A. laminar
B. turbulent
C. creeping
D. transition region

During crystallisation, formation of crystal can occur in
__________ solution only.
A. saturated
B. supersaturated
C. undersaturated
D. all (a), (b) and (c)

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

An insulator should have
A. low thermal conductivity.
B. high thermal conductivity.
C. less resistance to heat flow.
D. a porous structure.

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.

Choose the correct equation.
A. Nu = (Re) (Pr) (Gz)
B. Nu = (Re) (Pr) (St)
C. Nu = (Re)(Pr)
D. Nu = (Pr)(St)

In a forward feed multiple effect evaporator unit
A. viscosity of liquid is highest in first effect.
B. transfer from effect to effect is done by pumps.
C. no pump is required to withdraw the product from the
last effect.
D. none of these.

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

For heat flow through very thick walled cylinder, use ____ mean
radius.
A. arithmetic
B. logarithmic
C. geometric
D. either (a) or (c)

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.

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

Water is normally used as a coolant in the heat exchange
equipments mainly because of its
A. abundance & high heat capacity
B. low density
C. low viscosity
D. high fluidity

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.

Which of the following has maximum thermal conductivity at the
same temperature?
A. Steel
B. Petrol
C. Air
D. All have the same conductivity

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

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

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.

LMTD can’t be used as such without a correction factor for the
A. multipass heat exchanger.
B. baffled heat exchanger.
C. condensation of mixed vapour in a condenser.
D. all (a) (b) and (c).

For a cold viscous feed, backward feed gives __________ than
forward feed.
A. a higher capacity
B. a lower capacity
C. lower economy
D. none of these

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

In SI units, thermal conductivity is expressed in
A. Watt/m.°K
B. Watt/m2. °K
C. Watt/m2. °K
D. Watt/m4. °K

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

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

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

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

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

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.

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.

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

In SI units, fouling factor is expressed in
A. m2°K/W
B. W/m2°K
C. m2°K
D. m°K/W

An ejector is used to
A. increase pressure
B. increase temperature
C. remove condensate
D. none of these

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.

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

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

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

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

A black body does not __________ radiation.
A. absorb or emit
B. refract
C. reflect
D. both(b) & (c)

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.

Peclet number (Pe) is given by
A. Pe = Re.Pr
B. Pe = Re/Pr
C. Pe = Pr/Re
D. Pe = Nu.Re

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

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.

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 (a) (b) and (c).

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

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

View factor is important in heat transfer by
A. steady state conduction
B. natural convection
C. forced convection
D. radiation

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.

For a multipass shell and tube heat exchanger, the LMTD
correction factor is always
A. 1
B. > 1
C. < 1
D. between 1 & 2

If heat transfer rate varies with the time, it is termed as
A. forced convection
B. steady state conduction
C. monochromatic radiation
D. none of these

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.

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

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

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.

Agitated film evaporator is suitable for concentrating
__________ liquids.
A. foaming
B. viscous
C. very thin
D. corrosive

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 (a), (b) and (c)

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

Harmonic mean temperature difference is given by
A. sqrt(delta T1DeltaT2)
B. 2delta T1DeltaT2/ (delta T1+DeltaT2)
2delta T1*DeltaT2/ (delta T1-DeltaT2)

Arithmetic mean area can be used in heat transfer problem to
calculate the heat flow by conduction through a cylinder w/c 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).

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

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

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

Thermal diffusivity is given by
A. k/p Cp
B. ∙ p Cp/k
C.Cp u/ alpha
D.

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

Fourier’s law of heat conduction applies to __________
surfaces.
A. Isothermal
B. non-isothermal
C. both (a) and (b)
D. neither (a) and (b)

________ chart is known as transient heat conduction chart.
A. Dirhing’s
B. Heisler’s
C. Mollier’s
D. Cox

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.

Which of the following has the minimum thermal conductivity?
A. Nitrogen
B. Steel
C. Carbon black
D. Tar

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

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

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

Pick out the wrong statement:
A. The capacity of an evaporator is reduced by the boiling
point elevation.
B. Corrosive liquid is normally passed through the tubes
in a shell and tube heat exchanger.
C. Steam jet ejector is used for vapor compression in a
thermal recompression evaporator.
D. Heat sensitive materials should be concentrated in
high pressure evaporators.

Circulation pump is located below the evaporater to
A. avoid cavitation.
B. avoid frequent priming.
C. create more suction head.
D. none of these

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

Steam condensate is recovered by steam traps and recycled for
use as boiler feed water, because of its low
A. hardness
B. dissolved solids content
C. suspended solids content
D. all (a), (b) and(c)

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

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

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.

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

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. 2^0.8
B. 4^0.8
C. 4^0.4
D. 2^0.4

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

_________ 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

__________ paint has the minimum absorption co-efficient.
A. Black
B. White lead
C. Grey
D. Light cream

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.

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

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

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.

What is the absorptivity of a black body?
A. 1
B. 0
C. 0.78
D. 0.95

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

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.

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).

The advantage of backward feed multiple effect evaporators
over forward feed units is that
A. heat sensitive material can be handled.
B. there is no additional cost of pumping.
C. most concentrated liquid is at highest temperature.
D. equal heat transfer co-efficients exist in various
effects

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

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

Thermal conductivities of most of the liquids __________ with
rise in temperature.
A. increases
B. decreases
C. remains unchanged
D. may increase or decrease; depends on the liquid

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

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.

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

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.

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.

Removal of __________ heat is involved in the condensation of
a vapor under saturated conditions.
A. super
B. sensible
C. latent
D. both(b) & (c)

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. ΔT1/2
C. (ΔT)5/4
D. (ΔT)3/4

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

Prandtl and Reynold’s analogies are identical for Pr no. value of
A. 0
B. 0.5
C. 1
D. 5

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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

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.

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

A dephlegmator is a
A. total condenser
B. vacuum evaporator
C. partial condenser
D. double pipe heat exchangerC

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

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

In case of surface condensers, a straight line is obtained on
plotting 1/U vs. __________ on an ordinary graph paper.
A. 1/𝑽-0.8
B. 𝑽0.8
C. 𝑽-2
D. 1/𝑽-2

Thermal diffusivity is the most important in heat transfer by
A. conduction
B. radiation
C. condensation
D. natural convection

(NGr x NPr) is called the __________ number.
A. Graetz
B. Reyleigh
C. Nusselt
D. Stanton

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

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

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

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.

Evaporator tubes are generally
A. horizontal
B. vertical
C. inclined
D. random

In a boiling curve, the peak heat flux is called the _______ point.
A. Nusselt
B. Leidenfrost
C. boiling
D. burnout

For a counter current heat exchanger with Ti h = 80°C, T°c =
60°C, T°h = 50°C and Ti c = 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

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 2^2
C. increase by 2^16
D. remain unchanged

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.

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

Prandtl number is the ratio of
A. mass diffusivity to thermal diffusivity.
B. momentum diffusivity to thermal diffusivity.
C. thermal diffusivity to mass diffusivity.
D. thermal diffusivity to momentum diffusivity.

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

Heat flux, as defined in heat flow is analogous to __________ in
electricity flow.
A. current
B. voltage
C. resistance
D. none of these

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

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

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

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

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

Water always boils when its
A. temperature reaches 100° C.
B. vapour pressure equals 76 cm of Hg.
C. saturated vapour pressure equals the external
pressure on its surface.
D. saturated vapour pressure is less than the
atmospheric pressure.

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.

Which is the most suitable for cold viscous feed?
A. Forward feed
B. Backward feed
C. Mixed feed
D. Parallel feed

Dropwise condensation is promoted on a/an ________ surface.
A. glazed
B. oily
C. coated
D. smooth

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

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

(𝑁RE𝑁PR )(𝐷/𝐿) is called the __________ number
A. Peclet
B. Stanton
C. Graetz
D. none of these

Nucleate boiling is promoted
A. on polished surfaces
B. on rough surfaces
C. in the absence of agitation
D. none of these

In forced circulation, the heating element is injected
A. internally
B. externally
C. both (a) and (a)
D. neither (a) nor (b)

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

The equation, Nst = f/2, is the __________ analogy.
A. Colburn
B. Reynolds
C. Prandtl
D. none of these

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

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.

Stefen’s block body radiation law can also be derived from
__________ law.
A. Kirchoffs
B. Planck’s
C. Fourier’s
D. none of these

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.

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).

What is the emissivity of a black body?
A. 1
B. 0
C. 0.90
D. 0.5

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.

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

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

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’

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 (a), (b) and (c).

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

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

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.

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

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

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.

With increase in temperature, the total emissivity of conductors
A. increases
B. decreases
C. remains same
D. decreases linearly

Loss of heat from untagged steam pipe to the ambient air is by
A. conduction
B. convection
C. radiation
D. all (a), (b) & (c)

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

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.

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

Heat sensitive materials can be concentrated in an evaporator
employing
A. vacuum
B. high pressure
C. high residence time
D. none of these

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.

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.

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.

What is the logarithmic mean of r1 and r2 ?
A. r1 – r2 / ln (r1/r2)
B. r1 – r2 / ln (r2/r1)
C. r2 – r1 / ln (r1/r2)
D. r1 – r2 / - ln (r1/r2)

Maximum heat transfer rate is achieved in _______ flow.
A. co-current
B. counter-current
C. turbulent
D. Laminar

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

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

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