ht Flashcards
(503 cards)
1
Q
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).
A
all a b c
2
Q
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.
A
double pipe with fin on AIR side
3
Q
Which of the following is generally considered as opaque surface towards
radiations?
a. Gases
b. Solids
c. Liquids
d. Both (b) and (c)
A
both b and c
4
Q
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.
A
multiple effect evap only
5
Q
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
A
nucleate
6
Q
. 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
A
C/E
7
Q
Reynold’s analogy states that
a. Nst α f
b. Nst α NRe
c. NNu α f
d. NRe α f
A
a. Nst α f
8
Q
With increase in temperature, the thermal conductivity of non-metallic
amorphous solids
a. decreases
b. increases
c. remains constant
d. first decreases upto certain temperature and then increases
A
INCREASES
9
Q
Fourier’s law applies to the heat transfer by
a. convection
b. radiation
c. conduction
d. all (a), (b) & (c)
A
CONDUCTION
10
Q
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.
A
NONE OF THESE
11
Q
In the equation Q = UAΔt; Δt is
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.
A
logarithmic mean temperature difference
12
Q
With increase in porosity, the thermal conductivity of a solid substance
A
DECREASES
13
Q
For an ideal black body
a. absorptivity = 1
b. reflectivity = 1
c. emissivity = 0
d. transmissivity = 1
A
absorptivity = 1
14
Q
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
A
34.4
15
Q
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.
A
accounts for additional resistances to heat flow.
16
Q
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
A
DECREASES
17
Q
he steam ejector is used to
a. remove condensate from the steam pipelines.
b. create vacuum.
c. superheat the steam.
d. none of these
A
CREATE VACUUM
18
Q
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
A
PASSES THROUGH A MAXIMA
19
Q
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
A
(COP)R = 1.5; (COP)HP = 2.5
20
Q
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
A
32
21
Q
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.
A
relieve stresses caused by thermal expansion.
22
Q
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.
A
boiling of a liquid on a hot surface.
23
Q
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.
A
counter flow with process stream on shell side.
24
Q
Heat produced when a steady state current, I passes through an electrical
conductor having resistance, ‘R’ is
a. IR
b. I2R
c. IR2
d. I2R2
A
I2R
25
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.
HIGHLY TURBULENT
26
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).
ALL A B C
27
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)
MERCURY
28
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.
NONE OF THESE
29
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.
INCREASES
30
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.
FOAMING OF THE SOLUTION
31
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.
INCREASE THE SHELL SIDE HEAT TRANSFER COEFFICIENT
32
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.
finned tube heat exchanger with air OUTSIDE and steam inside.
33
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
W/m2°K
34
The number of kg vaporised per kg of steam fed to the evaporator is
defined as
ECONOMY
35
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
The equivalent diameter of heat transfer for a duct of square cross
section (having each side as 'x') is equal to 4x.
36
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
BOILING POINT ELEVATIONS
37
ncreasing 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.
DECREASED CAPACITY
38
The equivalent diameter for pressure drop is __________ that for heat
transfer.
a. smaller than
b. greater than
c. equal to
d. not related with
GREATER THAN
39
Controlling heat transfer film co-efficient is the one, which offers
__________ resistance to heat transfer.
a. no
b. the least
c. the largest
THE LARGEST
40
he 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
35
41
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.
n case of a 1 - 2 shell and tube heat exchanger, the LMTD
correction factor value increases sharply, when a temperature
cross occurs.
42
The average heat transfer co-efficient for laminar film condensation on
vertical surface is inversely proportional to (where, ΔT = Temperature drop
across condensate film )
a. (ΔT)2
b. ΔT
c. (ΔT)1/4
d. (ΔT)3/
T1/4
43
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.
MAINLY CONFINED TO A THIN FILM OF FLUID NEAR THE SURFACE
44
Which of the following is concerned with both heat and mass transfer ?
a. Lewis relationship
b. Nusselt number
c. Kutateladze number
d. Froude number
LEWIS RELATIONSHIP
45
A backward feed multiple effect evaporator is better than forward feed for
concentrating cold feed, because it provides
HIGHER ECONOMY
46
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.
Less than that of the uninsulated steam pipe.
47
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
LOGARITMIC MEAN AREA
48
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.
SCHMIDT
49
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.
GIVE LARGER AREA PER TUBE
50
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
may increase or decrease ; depends on the material
51
Which one gives the monochromatic emissive power for black body
radiation ?
PLANCKS LAW
52
For what value of Prandtl number, St = f/2?
1
53
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.
the temperature drops in the two fluids and the wall are
proportional to individual resistances
54
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.
fluids in TURBULENT FLOW
55
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).
ALL A B C
56
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.
Constant rate of fluid flow.
57
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
radiation becomes important
58
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)
ALL A B C
59
Temperature profile in steady state heat transfer is
a. asymptotic
b. hyperbolic
c. parabolic
d. linear
LINEAR
60
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.
INCREASES THE OVERALL HEAT TRANSFER COEFFICIENT
61
When vaporisation takes place through a blanketting film of gas, the
phenomenon is termed as __________ boiling.
a. pool
b. nucleate
c. transition
d. film
FILM
62
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
0.2D
63
Stefan-Boltzman law which describes the radiation heat transfer states
that, it is proportional to (where, t = temperature in °C T = absolute
temperature in ° K )
a. t4
b. T4
c. 1/t4
d. 1/T4
T4
64
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
4,36
65
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
Kcal/hr.m.°C
66
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
ALL BODIES
67
It is not preferable to use superheated steam in evaporators, because of
its very
a. high temperature
b. high pressure
c. low film co-efficient
d. none of these
LOW FILM COEFFICIENT
68
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
3.06 x l05
69
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.
cold fluid is heated to a certain temperature by condensing steam
(isothermal fluid).
70
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. NPr 1/3
c. NPr-1
d. NPr-1/3
NPr 1/3
71
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
0.5-50
72
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).
ALL A B C
73
The actual temperature drop across the heating surface of an evaporator
depends on the
a. liquid depth over the heating surface.
b. solution being evaporated.
c. pressure difference between the steam chest and the vapor space
above the boiling liquid.
d. all (a), (b) and (c)
ALL A B C
74
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)
HEAT BALANCE CONSIDERATION
75
he Graetz number is concerned with the
a. mass transfer between a gas and a liquid.
b. absorption with chemical reaction.
c. heat transfer in turbulent flow.
d. heat transfer in laminar flow.
IN LAMINAR FLOW
76
Solid angle subtended by the finite surface at the radiating element is called
angle of vision
77
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.
the emissivity of a surface decreases, if it gets corroded by
atmospheric environment.
78
In forced convection, the heat transfer depends on
a. Re, Pr
b. Re, Gr
c. mainly Gr
d. Re only
Re, Pr
79
With increase in temperature, the thermal conductivity of most liquids
decreases
80
Heat transfer by __________ may not necessarily require the presence of
a medium
radiation
81
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.
Logarithmic mean area is used for calculating the heat flow rate
through a thick walled cylinder.
82
In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used
in low range of temperature differences.
in high range of temperature differences.
because of its low cost.
to prevent corrosion of the tube bundles.
in high range of temperature differences.
83
Stefan-Boltzman law applies to __________ body.
black
84
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 vapor
some
85
In case of parallel flow heat exchanger, the lowest temperature
theoretically attainable by the hot fluid is __________ the outlet temperature of
the cold fluid.
equal to
86
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
heat exchanger
87
Which of the following is directly concerned with the heat transfer ?
a. Strouhal number
b. Sherwood number
c. Euler number
d. Grashoff number
grashof
88
Pick out the wrong statement:
a. With change in temperature, the radiant energy emitted by a black
body remains unchanged.
b. Absorptivity of a body approaches unity in case of diffuse
reflection.
c. Absorptivity of a perfectly black body is unity.
d. Value of Stefan-Boltzman constant is 4.876 x 10-8 KCal/m2.hr.°K4.
With change in temperature, the radiant energy emitted by a black
body remains unchanged.
89
Planck's distribution law is valid for __________ bodies.
a. black
b. white
c. coloured
d. all (a), (b) & (c)
COLORED
90
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
INCREASED
91
Radiation energy is emitted by all the substances, which are above
0K
92
What is the steam economy in case of a single effect evaporator system ?
< 1
93
2.
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
. ha = hl
b. ha = 2hl
c. ha = 0.5 hl
d. ha = 0.75 hl
ha = 2hl
94
4.
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
transient conduction
95
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
b. Q ∝ T4
96
Baffles are provided in heat exchangers to increase the
a. fouling factor
b. heat transfer area
c. heat transfer co-effient
c. heat transfer co-effient
97
7.200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000
seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5
x 10-3 kg/m2.s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid.
The interfacial area available for drying is 4 m2/1000 kg of dry solid. The moisture
content at the end of the drying period is (in kg moisture/kg dry solid)
a. 0.5
b. 0.05
c. 0.1
d. 0.15
0.1
98
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
temperature of the body
99
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
decreases
100
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.
both counter and parallel-flow of the fluids.
101
12.
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
<1
102
With increase in temperature, the thermal conductivity of steel
a. increases
b. decreases
c. remains unchanged
d. increases exponentially
decreases
103
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
a. None of these
Sieder-Tate
104
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'.
enhance turbulence
105
In a single effect evaporator, the economy is
a. 1
b. < 1
c. >1
d. none of these
<1
106
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
<1
107
Which of the following is not concerned with the heat transfer?
a. Brinkman number
b. Stanton number
c. Schmidt number
d. Peclet number
schmidt
108
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
180
109
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
1000
110
Crystallisation of solids from a homogeneous solution is a/an __________ process.
exothermic
111
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
24000
112
Value of Prandtl number for water ranges from
a. l to 2
b. 5 to 10
c. 100 to 500
d. 1000 to 2000
5 to 10
113
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 thes
conduction
114
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
partial ionization
115
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
backward
116
The sum of reflectivity and absorptivity for an opaque body is equal to
a. 0.5
b. 1
c. 0
d. 2
1
117
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
cumulatively increases
118
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
increases
119
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'
∝ 1/t
120
Heat transfer co-efficient (h1) for liquids increases with
a. increasing temperature.
b. decreasing temperature.
c. decreasing Reynolds number.
d. none of these.
increasing temperature
121
34.
A diathermaneous substance __________ the thermal radiation completely.
a. absorbs
b. reflects
c. transmits
d. none of these
transmits
122
A hot body will radiate heat most rapidly, if its surface is
black and rough
123
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
1-1.3
124
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
0.025
125
39.
A __________ surface has the maximum thermal emissivity out of the following.
a. black & smooth
b. black & rough
c. white & smooth
d. white & rough
black and rough
126
Radiant energy received by a body is proportional to (where, d = the distance between
the object emitting radiation and that receiving it.)
a. (d)^0.5
b. d
c. d2
d. d1.5
d2
127
Mechanical recompression evaporation is used in the production of
a. alcohol
b. distilled water
c. salt
d. fruits jam
distilled water
128
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 __________
brinkman number
129
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
0.45
130
44.
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
arrest the entrained liquid
131
45.
What is the thermal conductivity of a perfect heat insulator ?
0
132
46.
'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.
factor of safety
133
A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter
'd'. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow
conditions is proportional to
a. d0.8
b. d-0.2
c. d-1
d. d-1.8
b. d-0.2
134
Prandtl and Reynolds analogy are same, when Prandtl number is
a. 0.5
b. 1
c. >2
d. 1.5
1
135
Heat transfer occurs by natural convection because change in temperature causes
difference in
a. viscosity
b. density
c. thermal conductivity
d. heat capacity
density
136
The ratio of kinematic viscosity to thermal diffusivity is called the __________
number.
a. Peclet
b. Prandtl
c. Stanton
d. Nusselt
prandtl
137
1.
The critical radius 'r' of insulation on a pipe is given by
r = k/h
138
3.
If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds
number of the shell side fluid
decreases
139
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.
painting the surface white (with aluminium paint).
140
______ paint has the maximum absorption coefficient.
a. Black
b. Yellow
c. White
d. Grey
black
141
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 thes
. remove condensate and inert gases.
142
.
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
straight line
143
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.
none of these
144
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
Driving force = Rate x Resistance
145
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
Newton's law of cooling
146
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.
goes through a minimum
147
4.
Heat transfer rate per unit area is called
a. thermal conductivity
b. heat flux
c. heat transfer co-efficient
d. thermal diffusivity
heat flux
148
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.
none of these
149
16.
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
four times
150
17.
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
first increase then decrease
151
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
zero
152
19.
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
0.6 to 120
153
20.
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.
least at the outlet of the last effect.
154
21.
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
the heat transfer rate is low in view of the large temperature drop.
155
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
1
156
23.
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
W/mk2
157
24.
Film condensation is promoted on a/an __________ surface.
a. oily
b. coated
c. clean & smooth
d. dirty
clean and smooth
158
25.
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
prandtl
159
26.
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.
thermal boundary layer lies inside the concentration boundary layer.
160
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
catchall
161
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).
all
162
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
P and S
163
Which of the following has the highest thermal conductivity ?
a. Brick
b. Air
c. Water
d. Silver
Silver
164
Which of the following is unimportant in forced convection ?
a. Reynolds number
b. Prandtl number
c. Grashhoff number
d. none of these
Grashoff number
165
32.
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.
vertical hex with steam on SHELL side
166
33.
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 thes
reduce the CAPACITY
167
Dropwise condensation occurs on __________ surfaces.
a. clean and dirt free
b. smooth clean
c. contaminated cooling
d. polished
Contaminated cooling
168
36.
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
cross-sectional area
169
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.
Swenson-Walker crystalliser is a batch crystalliser.
170
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
b. 3 x l08
171
Heat flux is the time rate of heat transfer per unit
a. length
b. area
c. volume
d. none of these
area
172
Film boiling occurs at __________ pressure.
a. atmospheric
b. sub-atmospheric
c. negative
d. very high
very high
173
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.
resistance in series
174
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
constant temperature equal to that of the base
175
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.
get economical temperature difference by using moderate pressure steam.
176
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.
when heat transfer area required is very low, i.e (100-200 ft2).
177
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.
Heat transfer by radiation can not occur across an absolute volume.
178
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
series and parallel set of shell and tube
179
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.
Thermal conductance of a wall of thickness 'L', thermal conductivity 'k' and heat flow
area 'A' is kL/A.
180
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
between 0 and 1
181
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.
buoyancy to viscous forces
182
According to Reynolds analogy, Stanton number is equal to (where, f = Fanning
friction factor)
a. 2f
b. f
c. f/2
d. f/4
f/2
183
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
under thermal equilibrium
184
4.
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
1 and 0
185
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
d. α = 1; ε = 1
186
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.
c. S.I. unit of fouling factor is Watt/m2.°K.
187
8.
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
Cube
188
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.
remove non-condensable gases.
189
10.
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.
high co-efficient of thermal expansion.
190
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
pool
191
12.
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
>10
192
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
Re and PR
193
At what value of Prandtl number, the hydrodynamic and thermal boundary layers are
identical ?
a. 0.5
b. 1
c. 1.5
d. 80
1
194
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.
total amount of vapor produced per Kg of feed steam in a multiple effect system is
much higher than in a single effect.
195
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.
keeping the heat transfer surface clean.
196
Trap is used to remove __________ from steam pipe lines.
a. steam
b. condensate
c. non-condensables
d. none of these
CONDENSATE
197
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
160
198
Tube pitch is the __________ of tube diameters and the clearances.
a. sum
b. difference
c. ratio
d. none of these
sum
199
20.
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
decreases
200
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
less
201
Natural convection is characterised by
a. Grashhoff number
b. Peclet number
c. Reynolds number
d. Prandtl number
grashoff
202
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
4.364
203
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
<1
204
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
a. K/h0
205
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)^0.5
(ΔT)3
206
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.
0
207
body is called grey if the monochromatic emissivity of the body is
a. zero
b. unity
c. same for all wavelengths
d. different for all wavelengths
c. same for all wavelengths
208
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.
flows OUTSIDE the tubes
209
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.
infinity
210
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
none of these
211
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
By increasing the number of shell passes, the temperature cross in a shell and tube heat
exchanger can be prevented.
212
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
increased economy
213
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
linear
214
37.
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.
by heating an intermediate material (like chequor bricks) and then heating the air from
this hot material.
215
_________ equation relates the thermal conductivity of a solid to its temperature.
a. Antonie
b. Kopp's
c. Lee's
d. Kistyakowski
Lee's
216
9.
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^0.5
Δt
217
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.
. Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the
film co-efficient, which is higher.
218
Viscous & heat sensitive liquids are concentrated in __________ evaporators.
a. open pan
b. long tube
c. agitated film
d. none of these
agitated film
219
42.
1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C.
a. 1.49
b. 1
c. 4.88
d. none of these
1.49
220
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
none of these
221
the ratio of momentum diffusivity to thermal diffusivity is the __________ number.
a. Prandtl
b. Nusselt
c. Stanton
d. Grashoff
Prandtl
222
for a perfectly transparent surface (like gases), the
a. absorptivity = 0
b. transmissivity = 1
c. reflectivity = 0
d. all (a), (b) & (c)
transmissivity = 1
223
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
different
224
During crystallisation, formation of crystal can occur in __________ solution only.
a. saturated
b. supersaturated
c. undersaturated
d. all (a), (b) and (c)
supersaturated
225
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
4000
226
An insulator should have
a. low thermal conductivity.
b. high thermal conductivity.
c. less resistance to heat flow.
d. a porous structure
low thermal conductivity
227
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
feed flows from low pressure to high pressure
228
SECTION 6 1. Choose the correct equation.
a. Nu = (Re) (Pr) (Gz)
b. Nu = (Re) (Pr) (St)
c. Nu = (Re)(Pr)
d. Nu = (Pr)(St)
b. Nu = (Re) (Pr) (St)
229
2. 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.
d. none of these.
230
3. 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
c. parabolic
231
4. For heat flow through very thick walled cylinder, use____mean radius.
a. arithmetic
b. logarithmic
c. geometric
d. either (a) or (c)
b. logarithmic
232
5. 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.
b. there is no risk of contamination.
233
6. Water is normally used as a coolant in the heat exchange equipments mainly because ofits
a. abundance & high heat capacity
b. low density
c. low viscosity
d. high fluidity
a. abundance & high heat capacity
234
7. 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.
d. shape and porosity of the body.
235
8. Which of the following has maximum thermal conductivity at the same temperature?
a. Steel
b. Petrol
c. Air
d. All have the same conductivity
a. Steel
236
9. Maximum heat transfer rate is obtained in __________ flow.
a. laminar
b. turbulent
c. creeping
d. transition region
b. turbulent
237
10. 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
b. local
238
11. 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
d. 1/4
239
12. 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.
a. approach.
240
13. 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).
a. multipass heat exchanger.
241
14. Fqra cold viscous feed, backward feed gives __________ than forward feed.
a. a higher capacity
b. a lower capacity
c. lower economy
d. none of these
a. a higher capacity
242
15. 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
c. 81.25
243
16. 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
a. U1 = U2
244
17. In SI units, thermal conductivity is expressed in
a. Watt/m.°K
b. Watt/m2. °K
c. Watt/m2. °K
d. Watt/m4. °K
a. Watt/m.°K
245
18. 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
a. boiling point (at the same pressure)
246
19. 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
d. sum
247
20. 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
c. >0.6
248
21. 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
b. R2/(R1+R2)
249
22. 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
b. 0.794 h1
250
23. 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.
c. heat transfer area.
251
24. 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.
b. 4.88 kcal/hr. m.2°C.
252
25. 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
a. Molten sodium (a coolant used in fast breeder reactor)
253
26. In SI units, fouling factor is expressed in
a. m2°K/W
b. W/m2°K
c. m2°K
d. m°K/W
a. m2°K/W
254
27. An ejector is used to
a. increase pressure
b. increase temperature
c. remove condensate
d. none of these
d. none of these
255
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.
b. flexibility possible in the baffle arrangement.
256
29. 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
a. wall or skin friction
257
30. 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
b. 0.5 to 50
258
31. 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
d. Nu, Gz
259
32. 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
b. thickness
260
261
34. 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.
262
35. Peclet number (Pe) is given by
a. Pe = Re.Pr
b. Pe = Re/Pr
c. Pe = Pr/Re
d. Pe = Nu.Re
a. Pe = Re.Pr
263
36. 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
c. heat flux at the wall to that across the entire pipe.
264
37. 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.
b. momentum diffusivity to thermal diffusivity.
265
38. 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).
d. All (a) (b) and (c).
266
39. 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
c. Agitated film evaporator
267
40. "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
a. Kirchoffs
268
41. View factor is important in heat transfer by
a. steady state conduction
b. natural convection
c. forced convection
d. radiation
d. radiation
269
42. 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.
c. higher tube side heat transfer co-efficient.
270
43. For a multipass shell and tube heat exchanger, the LMTD correction factor is always
a. 1
b. >1
c. < 1
d. between 1 & 2
c. < 1
271
44. 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
d. none of these
272
273
46. 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
c. single pass fixed tube sheet
274
47. 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.
c. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger.
275
48. Agitated film evaporator is suitable for concentrating __________ liquids.
a. foaming
b. viscous
c. very thin
d. corrosive
b. viscous
276
49. The thickness of condensate layer in filmwise condensation depends on the
b. surface configuration
c. liquid flow rate from the surface
d. all (a), (b) and (c)
d. all (a), (b) and (c)
277
50. 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
a. parabolic
278
SECTION 7 1. 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
a. basket type
279
280
3.Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is
a. thin walled having the value of Ao Ai/< 2.
b. thick walled.
c. having the value of Ao/Ai > 2.
d. both (b) and (c).
a. thin walled having the value of Ao Ai/< 2.
281
4. 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
a. cube
282
5.Overall heat transfer co-efficient for cooling of hydrocarbons by water is about
b. 50 -100 W/m2 . °K
c. 50 -100 BTU/hr. ft.2°F
d. 1000 - 1500 BTU/hr. ft.2°F
c. 50 -100 BTU/hr. ft.2°F
283
6. 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
d. coke breeze
284
285
8.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
a. 1
286
9.Fourier's law of heat conduction applies to __________ surfaces.
a. isothermal
b. non-isothermal
c. both (a) and (b)
d. neither (a) and (b)
c. both (a) and (b)
287
10.__________ chart is known as transient heat conduction chart.
a. Dirhing's
b. Heisler's
c. Mollier's
d. Cox
a. Dirhing's
288
11. 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.
d. Temperature difference between the two surfaces of the wall.
289
12.Which of the following has the minimum thermal conductivity ?
a. Nitrogen
b. Steel
c. Carbon black
d. Tar
a. Nitrogen
290
13.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
a. a section of the exchanger in which change in temperature of one stream equals the average driving force in the section.
291
14.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
c. hf < hd
292
15.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.
d. Heat sensitive materials should be concentrated in high pressure evaporators.
293
16. 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
b. vacuum
294
17.Circulation pump is located below the evaporater to
a. avoid cavitation.
b. avoid frequent priming.
c. create more suction head.
d. none of these.
c. create more suction head.
295
18.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
c. Wien's displacement
296
19. Steam condensate is recovered by steam traps and recycled for use as
boiler feed water, because of its low
a. hardness
b. dissolved soilds content
c. suspended solids content
d. all (a), (b) and(c)
d. all (a), (b) and(c)
297
298
21. Duhring rule is important in solving problems on
a. distillation
b. crystallisation
c. evaporation
d. humidification
c. evaporation
299
22. 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
b. 0.75 D
300
23. 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.
a. large scale evaporation of liquor is needed.
301
24.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
b. 4^0.8
302
25.__________ 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.
a. Single pass, fixed tube sheet
b. U-tube
c. Three pass, fixed tube sheet
d. none of these
b. U-tube
303
26.In which mode of heat transfer, the Biot number is important ?
a. Transient heat conduction
b. Natural convection
c. Forced convection
d. Radiation
a. Transient heat conduction
304
27.__________ paint has the minimum absorption co-efficient.
a. Black
b. White lead
c. Grey
d. Light cream
b. White lead
305
28.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.
c. exit fluid temperature = wall temperature.
306
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
c. 400
307
30.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
a. Open pan evaporation
308
31.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.
b. temperature distribution is dependent on time.
309
32.What is the absorptivity of a black body ?
a. 1
b. 0
c. 0.78
d. 0.95
a. 1
310
33.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
c. forced convection
311
34.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.
c. should be less than the inside diameter of the shell.
312
313
36.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.
c. most concentrated liquid is at highest temperature.
314
37.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
d. Interfacial tension
315
38.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
d. None of these
316
39.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
b. decreases
317
40.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
d. 0.15
318
41.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.
a. avoid buckling of tubes.
319
42.1000 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
d. 51 min
320
43.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.
b. sum of all resistances.
321
44.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.
b. requirement of heat transfer area is low.
322
45.Removal of __________ heat is involved in the condensation of a vapor under saturated conditions.
a. super
b. sensible
c. latent
d. both(b) & (c)
c. latent
323
46.The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as
a. (ΔT)^1/4
b. ΔT^1/2
c. (ΔT)^5/4
d. (ΔT)^3/4
d. (ΔT)^3/4
324
47.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
b. decrease
325
48.Prandtl and Reynold's analogies are identical for Prandtl number value of
a. 0
b. 0.5
c. 1
d. 5
c. 1
326
49.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
b. excessive corrosion
c. uneconomic LMTD
d. decrease in heat exchanger efficiency
b. excessive corrosion
327
50.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.
c. both (a) and (b).
328
SECTION 8 1. 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
a. viscosity
329
330
3. Thermal diffusivity is the most important in heat transfer by
a. conduction
b. radiation
c. condensation
d. natural convection
a. conduction
331
4.(NGr x NPr) is called the __________ number.
a. Graetz
b. Reyleigh
c. Nusselt
d. Stanton
b. Reyleigh
332
5.A dephlegmator is a
a. total condenser
b. vacuum evaporator
c. partial condenser
d. double pipe heat exchanger
c. partial condenser
333
6.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
c. Black paint
334
7. 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
b. entrainment separator
335
336
9.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
c. increase by 2^16
337
10. 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. 5 minutes
338
11. 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.
d. none of these.
339
12. Evaporator tubes are generally
a. horizontal
b. vertical
c. inclined
d. random
b. vertical
340
341
14. In a boiling curve, the peak heat flux is called the __________ point.
a. Nusselt
b. Leidenfrost
c. boiling
d. burnout
d. burnout
342
15. 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.
b. Filmwise condensation takes place on non-wettable surfaces.
343
16. h.D/K is called the __________ number.
a. Nusselt
b. Peclet
c. Rayleigh
d. Grashoff
a. Nusselt
344
17. 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.
b. momentum diffusivity to thermal diffusivity.
345
18. 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
b. KA/x
346
19. Heat flux, as defined in heat flow is analogous to __________ in electricity flow.
a. current
b. voltage
c. resistance
d. none of these
a. current
347
20. 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
b. α 1/T
348
21. 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
b. twice
349
22. 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
c. mixed convection (both free and forced)
350
23. 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
c. facilitate removal of non-condensable gases
351
24. 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.
c. saturated vapour pressure equals the external pressure on its surface.
352
25. 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.
c. higher steam economy.
353
26. Which is the most suitable for cold viscous feed?
a. Forward feed
b. Backward feed
c. Mixed feed
d. Parallel feed
b. Backward feed
354
27. Dropwise condensation is promoted on a/an __________ surface.
a. glazed
b. oily
c. coated
d. smooth
b. oily
355
28. 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
d. viscous sub-layer
356
29. 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
a. increases
357
358
31. Nucleate boiling is promoted
a. on polished surfaces
b. on rough surfaces
c. in the absence of agitation
d. none of these
b. on rough surfaces
359
32. In forced circulation, the heating element is injected
a. internally
b. externally
c. both (a) and (a)
d. neither (a) nor (b)
a. internally
360
33. 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
b. 2
361
34. The equation, Nst = f/2, is the __________ analogy.
a. Colburn
b. Reynolds
c. Prandtl
d. none of these
b. Reynolds
362
35. 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
a. boiling point
363
36. 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.
d. none of these.
364
37. Stefen's block body radiation law can also be derived from __________ law.
a. Kirchoffs
b. Planck's
c. Fourier's
d. none of these
b. Planck's
365
38. 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.
c. to obtain higher heat transfer co-efficient and shorter tube.
366
367
40. 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.
b. condensate is corrosive in nature.
368
41. 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. At high fluid velocity
369
42. 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
b. (D))^-0.2
370
43.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
d. t = 800 s
371
44.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'
d. same in either 'a', b' or 'c'
372
45. 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).
d. all (a), (b) and (c).
373
46. Viscosity of gases __________ with increase in temperature.
a. increase very rapidly
b. increase slowly
c. decrease slowly
d. remain unaffected
b. increase slowly
374
47. What is the emissivity of a black body ?
a. 1
b. 0
c. 0.90
d. 0.5
a. 1
375
48. 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
b. horizontal tube
376
49. 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.
a. an oily surface.
377
50. 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
a. 0.1
378
SECTION 9 1. 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.
a. varies directly as the area and the LMTD.
379
2. With increase in temperature, the total emissivity of conductors
a. increases
b. decreases
c. remains same
d. decreases linearly
a. increases
380
3. Loss of heat from untagged steam pipe to the ambient air is by
a. conduction
b. convection
c. radiation
d. all (a), (b) & (c)
d. all (a), (b) & (c)
381
4. 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
b. falling film
382
5. 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. both the tube sheets fixed.
383
6. 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. 2^0.8
c. 2^0.2
d. 2^0.5
b. 2^0.8
384
7. Heat sensitive materials can be concentrated in an evaporator employing
a. vacuum
b. high pressure
c. high residence time
d. none of these
a. vacuum
385
8. 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.
b. more space.
386
9. 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.
a. large temperature differentials.
387
10. 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.
b. remove water resulting from partial condensation of steam.
388
11. 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
b. ha = 2hL
389
390
13. Maximum heat transfer rate is achieved in __________ flow.
a. co-current
b. counter-current
c. turbulent
d. laminar
c. turbulent
391
14.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
c. Wien's
392
15. 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
c. 70
393
16. Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger?
a. Corrosiveness & fouling characteristics
b. pressure
c. viscosity
d. density
d. density
394
395
18.The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy.
a.Colburn
b. Reynolds
c.Prandtl
d.none of these.
a.Colburn
396
19.The driving potential for the crystal growth during crystallisation is the __________ of the solution.
a. concentration
b.viscosity
c. super-saturation
d. density
c. super-saturation
397
20.jH factor for heat transfer depends upon the __________ number.
a. Biot
b. Nusselt
c. Reynolds
d. Prandtl
c. Reynolds
398
21. Kg of liquid evaporated per hour in an evaporator is defined as its
a. capacity
b. economy
c. steam load
d. none of these
a. capacity
399
22.Pick out the correct statement.
a. 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F.
b. In steady state heat conduction, the only property of the substance
which determines the temperature distribution, is the thermal
conductivity.
c. In unsteady state heat conduction, heat flows in the direction of temperature
rise.
d. In heat transfer by forced convection, Grashoff number is very important.
b. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity.
400
23. Open pan evaporators are preferred to be used, when the solution to be concentrated is
a. scaling
b. highly viscous
c. corrosive
d. salty
b. highly viscous
401
402
25. The maximum heat transfer co-efficient from steam heating will be attained when the steam is
a. supersaturated
b. saturated
c. wet
d. none of these
b. saturated
403
404
27.In a forward feed multiple effect evaporator, the pressure is
a. highest in last effect
b. lowest in last effect
c. same in all effects
d. dependent on the number of effects
b. lowest in last effect
405
28. In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will
a. increase
b. decrease
c. remain unchanged
d. either increase or decrease; depends on the coolant flow rate
c. remain unchanged
406
29. Which of the following situations can be approximated to a steady state heat transfer system ?
a. A red hot steel slab (having outside surface temperature as 1300°C) exposed
to the atmosheric air at 35°C.
b. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length
of stainless steel pipe exposed to atmospheric air at 35°C.
c. Boiling brine kept in open vessel when the bottom surface temperature of the
vessel is maintained constant at 180°C.
d. A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute
through a copper pipe exposed to atmospheric air at 35°C.
b. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C.
407
30. Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212°F may be around __________ BTU.
a. 180
b. 970
c. 3.97
d. data insufficient, can't be predicted
a. 180
408
31. The unit of conductance in SI unit is
a. W/m
b. W/m^2
c. W/°K
d. W/m°K
c. W/°K
409
32. In a shell and tube heat exchanger, square pitch compared to triangular pitch
a. gives a higher shell side pressure drop.
b. gives a lower shell side pressure drop.
c. can pack more surface area into a shell of given diameter.
d. none of these.
b. gives a lower shell side pressure drop.
410
33. Which of the following has maximum thermal conductivity ?
a. Iron
b. Coal
c. Nitrogen
d. Tar
a. Iron
411
34. A wall has two layers of materials A and B; each made of a different material.
Both the layers have the same thickness. The thermal conductivity of materialA
is twice that of B. Under the equilibrium, the temperature difference across the
wall is 36°C. The temperature difference across the layer A is __________ °C.
a. 6
b. 12
c.18
d. 24
b. 12
412
35.The film co-efficient between condensing vapour and metal wall increases
with
a. increasing temperature of the vapour.
b. decreasing temperature of the vapour.
c. increasing viscosity of the film of condensate.
d. increasing temperature drop.
a. increasing temperature of the vapour.
413
36. Critical value of the __________ number governs the transition from laminar
to turbulent flow in free convection heat transfer.
a. Grashoff
b. Reynolds
c. both 'a' & 'b'
d. Prandtl & Grashoff
d. Prandtl & Grashoff
414
37.The thermal boundary layer at NPr > 1
a. is thicker than hydrodynamic boundary layer.
b. is thinner than hydrodynamic boundary layer.
c. and the hydrodynamic boundary layer are identical.
d. disappears.
b. is thinner than hydrodynamic boundary layer.
415
38.In the free convection regime of pool boiling, the heat flux is proportional to
a. Δt^1/2
b. Δt^2
c. Δt^5/4
d. Δt
c. Δt^5/4
416
39.With increase in temperature, the thermal conductivity of fresh lubricating oil
a. increases
b. decreases
c. remains unchanged
d. may increase or decrease; depends on its composition
b. decreases
417
40.Fresh orange juice contains 12% (by weight) solids and the rest water 90%
of the fresh juice is sent to an evaporator to remove water and subsequently
mixed with the remaining 10% of fresh juice. The resultant product contains 40%
solids. The kg of water removed from 1 kg fresh juice is
a. 0.4
b. 0.5
c. 0.6
d. 0.7
d. 0.7
418
41. Nusselt number is the ratio of the temperature gradient at the wall to
a. temperature difference
b. heat flux
c. that across the entire pipe
d. none of these
c. that across the entire pipe
419
42.The Stefan-Boltzman constant depends on the
a. medium
b. temperature
c. surface
d. none of these
d. none of these
420
43.The units of resistance to heat transfer is
a. J.m-2.K-1
b. J.m-1.K-1
c. W.m-2.K-1
d. W-1m2K
d. W-1m2K
421
44. Thermal conductivity of a gas at low density, __________ with a. increase in temperature.
a. decreases
b. increases
c. remains unchanged
d. may increase or decrease; depends on the gas
b. increases
422
45. Nusselt number is a function of Prandtl number and __________ number of
fluid in natural convection heat transfer.
a. Grashoff
b. Biot
c.Stantan
d. Reynolds
a. Grashoff
423
46. __________ heat exchanger is used for chilling oil to be dewaxed.
a. U-tube
b. Double pipe
c. Fixed tube
d. Floating head
b. Double pipe
424
47. It is not recommended to use a 1-2 shell and tube heat exchanger for a
particular heat duty, whenever the LMTD correction factor is
a. > 0.75
b. < 0.75
c. < 0.50
d. < 0.25
b. < 0.75
425
48. Pick out the wrong statement.
a. Economy of a multiple effect evaporator is not influenced by the b. boiling
point elevation.
b. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature.
c. Double pipe heat exchangers are mostly used in the field of refrigeration.
d. Finned tube heat exchangers are suitable for heating air by steam.
b. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature.
426
49. In sub-cooled boiling,
a. temperature of the heating surface is less than the boiling point of the liquid.
b. temperature of the heating surface is more than the boiling point of the liquid.
c. bubbles from heating surface are absorbed by the mass of the liquid.
d. very large vapour space is necessary.
b. temperature of the heating surface is more than the boiling point of the liquid.
427
50. With increase in temperature, the thermal conductivity of a gas
a. increases.
b. decreases.
c. remains same.
d. may increase or decrease depending on the type of gas.
a. increases.
428
SECTION 10 1. A __________ evaporator employs an annular downtake.
a. basket type
b. horizontal
c. long tube vertical
d. none of these
a. basket type
429
2. Radiation heat losses from satisfactorily insulated high pressure
boilar may be about __________ percent.
a. 1
b. 7
c. 18
d. 26
b. 7
430
3. In natural convection heat transfer, the correlating parameter is the
a. Graetz number
b. Eckert number
c. Grashoff number
d. Bond number
c. Grashoff number
431
4. Boiling of milk in an open vessel is an example of __________
boiling.
a. film
b. sub-cooled
c. saturated nucleate
d. none of these
a. film
432
5. Pick out the wrong statement.
a. In process heat exchangers, saturated steam is preferred over the superheated steam.
b. The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of λ1. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 λ1.
c. When a vertical plate is heated in infinite air environmental under natural convection conditions, the velocity profile in air, normal to the plate, exhibits a maximum.
d. A body at 925 K emits an energy of 1.42 x 1011σW/m2 (σ is the
Stefan-Boltzman constant) in the wavelength band between 3 μm to 4 μm. The fraction of this energy in the total energy emitted over the entire wavelength range is equal to emissivity.
b. The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of λ1. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 λ1.
433
6. Mode of heat transfer involved in the cooling of air cooled internal
combustion engine is
a. conduction
b. natural convection
c. forced convection
d. none of these
b. natural convection
434
7. Steady state one dimensional heat flow by conduction as given by
Fourier's low does not assume that
a. there is no internal heat generation.
b. boundary surfaces are isothermal.
c. material is anisotropic.
d. constant temperature gradient exists.
c. material is anisotropic.
435
8. The left face of a one dimensional slab of thickness 0.2 m is
maintained at 80°C and the right face is exposed to air at 30°C.
The thermal conductivity of the slab is 1.2 W/m.K and the heat
transfer co-efficient from the right face is 10 W/m2.K. At steady
state, the temperature of the right face in °C is
a. 77.2
b. 71.2
c. 63.8
d. 48.7
d. 48.7
436
9. In a shell and tube heat exchanger, the shell side fluid velocity can
not be changed by changing the
a. tube layout
b. tube diameter
c. tube pitch
d. no. of baffles
b. tube diameter
437
10. To reduce the tube side pressure drop for the same flow rate, the
heat exchanger recomended is
a. 1-2 heat exchanger
b. 1-1 heat exchanger
c. 3-2 heat exchanger
d. 2-4 heat exchanger
b. 1-1 heat exchanger
438
439
12. Steam side heat transfer co-efficient in an evaporator is in the
range of __________ kcal/hr.m2°C.
a. 10-50
b. 100-500
c. 1000-1500
d. 5000-15000
d. 5000-15000
440
13. Correction is applied to LMTD for __________ flow.
a. parallel
b. counter
c. cross
d. none of these
c. cross
441
14. If h1 = inner film co-efficient and /h2 = outer film co-efficient, then
the overall heat transfer co-efficient is
a. always less than h1
b. always between h1 and h2
c. always higher than h2
d. dependent on metal resistance
b. always between h1 and h2
442
15. One kilogram of water at 0°C is changed to superheated steam of
one atm pressure and 300° C. The major heat consumption in the
process will be to
a. heat the water from 0°C to 100°C.
b. evaporate the water.
c. to superheat the steam.
d. data insufficient, can't be predicted
b. evaporate the water.
443
16. For __________ Prandtl number values, the heat conduction will
be negligible in the buffer zone.
a. extremely low
b. low
c. high
d. no
c. high
444
17. The radiation heat flux from a heating element at a temperature of
800°C, in a furnace maintained at 300°C is 8 kW/m2. The flux,
when the element temperature is increased to 1000°C for the
same furnace temperature is
a. 11.2 kW/m^2
b. 12.0 kW/m^2
c. 14.6 kW/m^2
d. 16.5 kW/m^2
d. 16.5 kW/m^2
445
18. Heat exchangers operating, when the asymptotic range is reached,
a. provide very large heat transfer co-efficient.
b. results in making part of the heating surface inactive.
c. results in abruptly increased velocity.
d. none of these.
b. results in making part of the heating surface inactive.
446
19. In case of a shell and tube heat exchanger, the minimum and
maximum baffle spacing is respectively (where, D = inside
diameter of the shell)
a. D/5 and D
b. D/2 and 2 D
c. D/4 and 2 D
d. D and 2 D
a. D/5 and D
447
20. In case of heat transfer by conduction in a hollow cylinder,
__________ mean area is used to calculate the heat transfer rate.
a. geometric
b. arithmetic
c. logarithmic
d. either (a), (b) or (c)
c. logarithmic
448
21. In a gas-liquid shell and tube heat exchanger, the
a. presence of a non-condensible gas decreases the condensing film
co-efficient.
b. gases under high pressure are routed through the tube side,
because high pressure gases are corrosive in nature.
c. gases to be heated/cooled is normally routed through the shell
side, because the corrosion caused by the cooling water or steam
condensate remain localised to the tubes.
d. all 'a', 'b' & 'c'
d. all 'a', 'b' & 'c'
449
22. Which is the most suitable for the concentration of foamy & frothy
liquors ?
a. Agitated film evaporator
b. Long tube vertical evaporator
c. Open pan evaporator
d. None of these
b. Long tube vertical evaporator
450
23. Boiling point elevation of an ideal solution
a. increases rapidly with temperature rise.
b. decreases rapidly with temperature rise
c. in independent of pressure.
d. both (b) and (c).
a. increases rapidly with temperature rise.
451
24. The rate of heat transfer is a product of overall heat transfer co
efficient, the difference in temperature and the
a. heating volume
b. heat transfer area
c. Nusselt number
d. none of these
b. heat transfer area
452
25. Which of the following has the lowest overall heat transfer co
efficient ?
a. Dowtherm
b. Molten sodium
c. Water
d. Air
d. Air
453
26. Which of the following has the minimum absorptivity ?
a. Aluminium foil
b. Coal dust
c. Refractory bricks
d. Iron plates
a. Aluminium foil
454
27. A black body when hot, emits heat radiation of __________
wavelengths.
a. small
b. large
c. all
d. one fixed
c. all
455
28. A composite wall consists of two plates A and B placed in series
normal to the flow of heat. The thermal conductivities
are kA and kB and the specific heat capacities are CPA and CPB for
plates A and B respectively. Plate B has twice the thickness of
plate A. At steady state, the temperature difference across plate A
is greater than that across plate B, when
a. CPA > CPB
b. CPA < CPB
c. kA < 0.5kB
d. kA>2 kB
c. kA < 0.5kB
456
29. Vibrations in the tubes of a shell and tube heat exchanger is
induced due to the
a. flow of fluid on the tube and shell sides.
b. oscillations in the flow of shell/tube sides fluid.
c. vibrations transmitted through piping and/or supports due to
external reasons.
d. all (a), (b) and (c)
d. all (a), (b) and (c)
457
30. Heat transfer by conduction in the turbulent core of a fluid flowing
through a heated pipe is negligible, if the value of Prandtl number
is
a. 0.2
b. 0.4
c. 0.6
d. 0.8
c. 0.6
458
31. The Nusselt number for fully developed (both thermally and
hydrodynamically) laminar flow through a circular pipe whose
surface temperature remains constant is
a. 1.66
b. 88.66
c. 3.66
d. dependent on NRe only
c. 3.66
459
32. Sensible heat of hot industrial flue gases can not be recovered by
a/an
a. economiser
b. regenerator
c. ceramic recuperator
d. none of these
d. none of these
460
33. The critical radius of insulation for a spherical shell is (where, K =
thermal conductivity of insulating material h0 = heat transfer
coefficient at the outer surface)
a. K/h0
b. 2K/h0
c. h0/K
d. h0/2K
b. 2K/h0
461
34. Radiator of an automobile engine is a __________ type of heat
exchanger.
a. co-current
b. cross-current
c. counter-current
d. direct contact
d. direct contact
462
35. In pipe flow, heat is transferred from hot wall to the liquid by
a. conduction only.
b. forced convection only.
c. forced convection and conduction.
d. free and forced convection.
c. forced convection and conduction.
463
36. The value of Stefan-Boltazman constant in SI unit is
a. 5.6697 x 10-8W/m2.°K4
b. 0.1714 x 10-8W/m2.°K4
c. 5.6697 x 10-8kcal/m2 . °K4
d. 0.1714 x 10-8kcal/m2. °K4
a. 5.6697 x 10-8W/m2.°K4
464
37. The unit of heat transfer co-efficient is
a. BTU/hr. ft2°F
b. BTU/hr. °F. ft.
c. BTU/hr. °F
d. BTU/hr. ft
a. BTU/hr. ft2°F
465
38. For turbulent flow in a tube, the heat transfer co-efficient is
obtained from the Dittus-Boelter correlation. If the tube diameter is
halved and the flow rate is doubled, then the heat transfer co
efficient will change by a factor of
a. 1
b. 1.74
c. 6.1
d. 37
c. 6.1
466
39. The inner wall of a furnace is at a temperature of 700°C. The
composite wall is made of two substances, 10 and 20 cm thick with
thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The
ambient air is at 30°C and the heat transfer co-efficient between
the outer surface of wall and air is 20 W.m-2.°C-1. The rate of heat
loss from the outer surface in W.m-2is
a. 165.4
b. 167.5
c. 172.5
d. 175
a. 165.4
467
40. Value of Nusselt number [Nu = (hD/k)] for the heat transfer by
conduction from a droplet or a spherical particle to a surrounding
stagnant film is
a. 0.5
b. 2
c. 10
d. 100
b. 2
468
41. Low thermal conductivity of heat insulating materials is due to its
a. dense structure.
b. high proportion of air space.
c. high specific heat.
d. none of these.
b. high proportion of air space.
469
42. The most conducive surface for dropwise condensation to occur is
the __________ surface.
a. coated
b. oily
c. glazed & polished
d. smooth
b. oily
470
43. In an interphase heat transfer process, the equilibrium state
corresponds to equality of temperature in the two phases, while the
condition for equilibrium in an interphase mass transfer process is
equality of
a. concentrations
b. chemical potentials
c. activity co-efficients
d. mass transfer co-efficients
a. concentrations
471
44. Calburn analogy is applicable for the value of Prandtl number from
a. 0.001 to 1
b. 0.6 to 120
c. 0.5 to 5
d. 120 to 400
b. 0.6 to 120
472
45. Pick out the correct equation.
a. jH = (St)(Pr)2/3 = f/2
b. jH = (St)(Pr)1/3 = f/2
c. jH = (St)2/3(Pr) = f/2
d. jH = (St)1/3(Pr) = f/2
a. jH = (St)(Pr)2/3 = f/2
473
46. Multiple effect evaporators ar used to
a. increase the steam economy & decrease the capacity.
b. increase the steam economy & the capacity.
c. decrease the steam economy & the capacity.
d. decrease the steam economy & increase the capacity.
b. increase the steam economy & the capacity.
474
475
48. Small scale evaporation is done in a
a. heat exchanger
b. condenser
c. multiple effect evaporator
d. steam jacketed kettle
d. steam jacketed kettle
476
49. Heat exchanger tubes are never made of
a. plain carbon steel
b. stainless steel
c. lead
d. copper
c. lead
477
50. At constant temperature, the thermal conductivities of gases
__________ with rise in pressure.
a. decrease
b. increase
c. remain unchanged
d. may increase or decrease; depends on the pressure
a. decrease
478
SECTION 11
479
2. In a cooling tower, water becomes cool by
a. loosing sensible heat.
b. heat transfer to surroundings.
c. vaporisation due to heat loss to air.
d. loosing latent heat.
a. loosing sensible heat.
480
3. In Fourier's law, the proportionality constant is called the
a. heat transfer co-efficient
b. thermal diffusivity
c. thermal conductivity
d. Stefan-Boltzman constant
c. thermal conductivity
481
4. The heat transfer co-efficient in film type condensation is
__________ that for dropwise condensation.
a. greater than
b. lower than
c. is same as
d. half
b. lower than
482
5. Pick out the wrong statement.
a. Bubble size increases with the dynamic viscosity of the liquid in
case of nucleate pool boiling.
b. Thermal conductivity of a dry material is more than that of the
damp material.
c. Ratio of its capacity to economy equals the steam consumption in
kg/hr in an evaporator.
d. Vaporisation of organic substances in evaporator mostly causes
foam formation.
b. Thermal conductivity of a dry material is more than that of the damp material.
483
6. 'Duhring's plot' is of use in
a. extractive distillation
b. evaporation
c. leaching
d. absorption
b. evaporation
484
7. Which has the lowest Prandtl number ?
a. Liquid metal
b. Aqueous solution
c. Water
d. Lube oil
a. Liquid metal
485
a. The value of hydrostatic head increases with increase in vacuum in
the effect in a multiple effect evaporator system.
b. Entering velocity of the liquid in the tubes of natural circulation
evaporators is in the range of 0.3 to 0.9 metre/second.
c. Duhring's plot is used for calculating the concentration of
solution.
d. In a multiple effect evaporation system, the number of effects is
limited by the total boiling point rise.
c. Duhring's plot is used for calculating the concentration of
solution.
486
9. Prandtl number for most of dry gases is about
a. 0.001
b. 0.72
c. 70
d. 150
b. 0.72
487
10. Prandtl number is the reciprocal of
a. Thermal diffusivity/Momentum diffusivity
b. thermal diffusivity x Momentum
c. Thermal diffusivity x Mass diffusivity
d. Mass diffusivity x Momentum diffusivity
a. Thermal diffusivity/Momentum diffusivity
488
11. In a heat exchanger with steam outside the tubes, a liquid gets
heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the
flow velocity is reduced to 1 m/s, other things remaining the same,
the temperature of the exit liquid will be
a. less than 45°C
b. more than 45°C
c. equal to 45°C
d. initially decreases and remains constant thereafter.
b. more than 45°C
489
490
13. Multiple effect evaporation accounts for
a. steam economy
b. lower operating costs
c. investment economy
d. none of these
a. steam economy
491
14. In case of a supercooled solution, which is on the verge of
crystallisation, the free energy of the solution as compared to that
of the solid is
a. more
b. less
c. same
d. more or less; depends on the nature of solution
a. more
492
15. Maximum water velocity in tubes of a 1-2 shell and tube heat
exchanger may be around __________ metres/second.
a. 1
b. 10
c. 20
d. 30
a. 1
493
16. In Biot number, the characteristic length used is the ratio of the
__________ of the solid.
a. volume to surface area
b. perimeter to surface area
c. surface area to volume
d. surface area to perimeter
a. volume to surface area
494
17. Which of the following is the most widely used heat insulating
material for pipelines carrying steam ?
a. Tar dolomite bricks followed by asbestos.
b. Fireclay refractory followed by aluminium sheet.
c. Cotton followed by aluminium foil.
d. 85% magnesia cement and glass wool.
d. 85% magnesia cement and glass wool.
495
18. Heat transfer co-efficient equation for forced convection, Nu =
0.023 Re0.8 . Pr n, is not valid, if the value of
a. n = 0.4 is used for heating.
b. n = 0.3 is used for cooling.
c. Reynolds number for the flow involved is > 10000.
d. Reynolds number for the flow involved is < 2100.
d. Reynolds number for the flow involved is < 2100.
496
19. Which is the best tube arrangement (in a shell and tube heat
exchanger) if the fluids are clean and non-fouling ?
a. Square pitch
b. Triangular pitch
c. Diagonal square pitch
d. None of these
b. Triangular pitch
497
20. In case of a multipass shell and tube heat exchanger, the
temperature drop in the fluid
a. is inversely proportional to the resistance across which the drop
occurs.
b. and the wall are proportional to individual resistances.
c. and the wall is not related.
d. none of these.
b. and the wall are proportional to individual resistances.
498
21. The purpose of providing expansion bellows in the shell of tubular
exchanger is to
a. increase the heating load.
b. impart structural strength.
c. account for the uneven expansion of shell and tube bundles.
d. facilitate increase of shell length, if needed.
c. account for the uneven expansion of shell and tube bundles.
499
500
23. Grashhoff number is given by
a. gD^3.β.Δtρ^2/μ^2
b. gD^2βΔtρ/μ^2
c. gD^2βΔtP^2μ
d. gD^3βΔtP^2/μ
a. gD^3.β.Δtρ^2/μ^2
501
24. The overall heat transfer co-efficient for a shell and tube heat
exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling
factor after one year of operation is found to be hd0 = 2000 W/m2.K.
The overall heat transfer co-efficient at this time is
a. 1200W/m^2.K
b. 894W/m^2.K
c. 333W/m^2.K
d. 287 W/m^2.K
c. 333W/m^2.K
502
25. In a laboratory test run, the rate of drying was found to be 0.5 x 10
3 kg/m2.s, when the moisture content reduced from 0.4 to 0.1 on
dry basis. The critical moisture content of the material is 0.08 on a
dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same
material under identical conditions. The surface area of the
material is 0.04 m2/kg of dry solid. The time required (in seconds)
to reduce the moisture content of the solids from 0.3 to 0.2 (dry
basis) is
a. 2000
b. 4000
c. 5000
d. 6000
c. 5000
503
26. Pick out the wrong statement.
a. 'Solvates' are chemical compounds formed by solute with their
solvents. When water is the solvent, then it is called a 'hydrate'.
b. In heat exchanger calculations (Δt)weighted is used in place of Δt,
when it involves more than one sequence of heating or cooling i.e.,
desuperheating & condensation or condensation & sub-cooling.
c. Heat transfer co-efficient during nucleate boiling is not
influenced by the agitation imparted.
d. In case of short tube vertical evaporators, area of central downtake
is about 50 to 100% of the total tube cross-sectional area.
c. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted.
