Heat Transfer Flashcards
(140 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
d) all (a), (b) and (c).
2
Q
Heat waves
a) can not pass through vacuum.
b) travel in straight line.
c) can be reflected by a mirror.
d) both (b) and (c).
A
d) both (b) and (c).
3
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
c) double pipe type with fin on air side.
4
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
d) Both (b) and (c)
5
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
c) multiple effect evaporator.
6
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
b) nucleate boiling
7
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
d) 1/CE
A
a) C/E
8
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
9
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
b) increases
10
Q
Fourier’s law applies to the heat transfer by
a) convection
b) radiation
c) conduction
d) all (a), (b) & (c)
A
c) conduction
11
Q
Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
baffle spacing & shell diameter.
a) tube diameter & pitch.
b) viscosity, density & mass
c) velocity of shell side fluid.
d) none of these.
A
d) none of these.
12
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
c) logarithmic mean temperature difference.
13
Q
With increase in porosity, the thermal conductivity of a solid substance
a) increases
b) decreases
c) remains unchanged
d) may increase or decrease; depends on the solid
A
b) decreases
14
Q
For an ideal black body
a) absorptivity = 1
b) reflectivity = 1
c) emissivity = 0
d) transmissivity = 1
A
a) absorptivity = 1
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
c) 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
b) decreases
17
Q
The steam ejector is used to
a) remove condensate from the steam pipelines.
b) create vacuum.
c) superheat the steam.
d) none of these.
A
b) 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
d) passes through a maxima
19
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
c) relieve stresses caused by thermal expansion.
20
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
d) boiling of a liquid on a hot surface.
21
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
a) counter flow with process stream on shell side.
22
Q
Heat produced when a steady state current, I passes through an electrical conductor having resistance, ‘R’ is
a) IR
b) (I^2)R
c) IR^2
d) (I^2)(R^2)
A
b) (I^2)R
23
Q
Pick out the wrong statement.
a) Orifice baffles are never used in a shell and tube heat exchanger.
b) Pressure drop on the shell side of a heat exchanger depends upon tube pitch also.
c) In a horizontal tube evaporator, surface blanketing by air is avoided.
d) Split ring type and pull through type floating heads are two commonly used floating heads is heat exchangers.
A
a) Orifice baffles are never used in a shell and tube heat exchanger.
24
Q
Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.
a) laminar
b) transition
c) both ‘a’ & ‘b’
d) highly turbulent
A
d) highly turbulent
25
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).
d) all (a), (b) and (c).
26
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)
b) mercury
27
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.
d) none of these.
28
Kirchoff s law applies to __________ radiation.
a) total
b) monochromatic
c) both (a) & (b)
d) neither (a) nor (b)
c) both (a) & (b)
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.
a) 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.
c) 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.
c) increase the shell side heat transfer co-efficient.
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.
b) finned tube heat exchanger with air outside and steam inside.
33
The unit of heat transfer co-efficient in SI unit is
a) J/M^2°K
b) W/m^2°K
c) W/m°K
d) J/m°K
b) W/m^2°K
34
The number of kg vaporised per kg of steam fed to the evaporator is defined as
a) capacity
b) rate of evaporation
c) economy
d) rate of vaporisation
c) 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.
b) 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
a) boiling point elevations
37
Increasing the liquor level in the evaporator results in the
a) decreased capacity.
b) increase in liquor film co-efficient.
c) decreased effect of hydrostatic head.
d) increased true temperature drop.
a) 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
a) smaller 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
d) lower
c) the largest
40
Thermal conductivity of a conducting solid material depends upon its
a) temperature
b) porosity
c) both (a) & (b)
d) neither (a) nor (b)
c) both (a) & (b)
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.
c) In 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)^(3/2)
c) (ΔT)^(1/4)
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.
c) 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
a) Lewis relationship
45
A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides
a) higher economy
b) lower capacity
c) both (a) & (b)
d) lower economy
a) higher economy
46
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
a) Logarithmic mean area
47
Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place
a) between two bodies in physical contact with each other.
b) between two bodies not in physical contact with each other.
c) from one part of a body to the another part of the same body.
d) both 'b' & 'c'
b) between two bodies not in physical contact with each other.
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.
c) Schmidt number.
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.
a) 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
d) may increase or decrease ; depends on the material
51
Which one gives the monochromatic emissive power for black body radiation?
a) Planck's law
b) Kirchhoffs law
c) Wien's law
d) Stefan-Boltzman law
a) Planck's law
52
For what value of Prandtl number, St = f/2?
a) 1.5
b) 1
c) > 1
d) < 1
b) 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.
a) 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.
b) for fluids in tubulent 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).
d) all (a), (b) and (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.
b) 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
c) 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)
d) all (a), (b) & (c)
59
Temperature profile in steady state heat transfer is
a) asymptotic
b) hyperbolic
c) parabolic
d) linear
d) 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.
c) 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
d) 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
a) 0.2 D
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) t^4
b) T^4
c) 1/(t^4)
d) 1/(T^4)
b) T^4
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
b) 4.36
65
What is the unit of thermal conductivity ?
a) Kcal/hr*m^2*°C
b) Kcal/hr*m*°C
c) Kcal/hr*m
d) Kcal/hr*°C
b) 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
b) 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
c) low film co-efficient
68
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.
a) cold fluid is heated to a certain temperature by condensing steam (isothermal fluid).
69
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)
b) NPr^(1/3)
70
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
b) 0.5-50
71
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).
d) all (a), (b) and (c).
72
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.
pressure difference between the
c) steam chest and the vapor space above the boiling liquid.
d) all (a), (b) and (c)
d) all (a), (b) and (c)
73
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)
a) heat balance consideration
74
The 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.
d) heat transfer in laminar flow.
75
Solid angle subtended by the finite surface at the radiating element is
a) called the view factor.
b) called the angle of vision.
c) proportional to the square of the distance between surfaces.
d) expressed in terms of radians.
b) called the angle of vision.
76
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.
a) The emissivity of a surface decreases, if it gets corroded by atmospheric environment.
77
In forced convection, the heat transfer depends on
a) Re, Pr
b) Re, Gr
c) mainly Gr
d) Re only
a) Re, Pr
78
With increase in temperature, the thermal conductivity of most liquids
a) increases
b) decreases
c) remains same
d) first increases upto a certain temperature and then becomes constant
b) decreases
79
Heat transfer by __________ may not necessarily require the presence of a medium.
a) conduction
b) natural convection
c) forced convection
d) radiation
d) radiation
80
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.
b) Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder.
81
In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used
a) in low range of temperature differences.
b) in high range of temperature differences.
c) because of its low cost.
d) to prevent corrosion of the tube bundles.
b) in high range of temperature differences.
82
Stefan-Boltzman law applies to __________ body.
a) black
b) white
c) grey
d) any colour
a) black
83
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
c) some
84
A perfect black body is a perfect __________ of radiation.
a) absorber
b) emitter
c) both (a) & (b)
d) neither (a) nor (b)
c) both (a) & (b)
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.
a) equal to
b) more than
c) less than
d) either more or less than (depending upon the fluid)
a) 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
b) 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
d) Grashoff number
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/m^2*hr*°K^4.
a) 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)
c) coloured
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
a) increased
91
Radiation energy is emitted by all the substances, which are above
a) 0°K
b) 0°C
c) 100°C
d) room temperature
a) 0°K
92
The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emis-sivities εx & εy is given by
a) εx + εy
b) εx * εy
c) (1/εx) + (1/εy)
d) (εx + εy) / (εx + εy - εx * εy)
d) (εx + εy) / (εx + εy - εx * εy)
93
What is the steam economy in case of a single effect evaporator system?
a) 1
b) >1
c) < 1
d) 0.1
c) < 1
94
If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length
a) ha = hl
b) ha = 2hl
c) ha = 0.5 hl
d) ha = 0.75 hl
b) ha = 2hl
95
jH factor for heat transfer is not a function of the __________ number.
a) Reynolds
b) Nusselt
c) Grashoff
d) both (b) & (c)
d) both (b) & (c)
96
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
c) transient conduction
97
Baffles are provided in heat exchangers to increase the
a) fouling factor
b) heat transfer area
c) heat transfer co-efficient
d) heat transfer rate
c) heat transfer co-efficient
98
In case of a vertical tube evaporator, with increase in the liquor level, the
a) capacity of the evaporator is decreased.
b) capacity of the evaporator is increased.
c) true temperature drop increases.
d) both (b) and (c).
a) capacity of the evaporator is decreased.
99
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
c) temperature of the body
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.
c) both counter and parallel-flow of the fluids.
101
In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always
a) < 1
b) > 1
c) 1
d) ∞
a) < 1
102
With increase in temperature, the thermal conductivity of steel
a) increases
b) decreases
c) remains unchanged
d) increases exponentially
b) 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
d) None of these
b) Sieder-Tate equation
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'.
b) enhance turbulence.
105
In a single effect evaporator, the economy is
a) 1
b) < 1
c) > 1
d) none of these
b) < 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
d) <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
c) Schmidt number
108
In counter flow compared to parallel flow,
a) LMTD is greater.
b) less surface area is required for a given heat transfer rate.
c) both (a) and (b).
d) more surface area is required for a given heat transfer rate.
c) both (a) and (b).
109
Crystallisation of solids from a homogeneous solution is a/an __________ process.
a) exothermic
b) mildly endothermic
c) highly endothermic
d) none of these
a) exothermic
110
Value of Prandtl number for water ranges from
a) 1 to 2
b) 5 to 10
c) 100 to 500
d) 1000 to 2000
b) 5 to 10
111
112
Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by
a) eddies current
b) conduction
c) convection
d) none of these
b) conduction
113
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
c) partial ionisation
114
Reynold's analogy states that (where, St = Stanton number f = friction factor)
a) St = f/2
b) St = f/4
c) St = 4f
d) St = f1/2
a) St = f/2
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
b) backward
116
The sum of reflectivity and absorptivity for an opaque body is equal to
a) 0.5
b) 1
c) 0
d) 2
b) 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
a) cummulatively 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
a) 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'
b) ∝ 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.
a) increasing temperature.
121
A diathermaneous substance __________ the thermal radiation completely.
a) absorbs
b) reflects
c) transmits
d) none of these
c) transmits
122
A hot body will radiate heat most rapidly, if its surface is
a) white & rough
b) black & rough
c) white & polished
d) black & polished
b) black & 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
b) 1-1.3
124
Analogy between mass and heat transfer is not applicable in case of
a) same velocity profile or equal eddy diffusivities.
b) thermal or pressure mass diffusion.
c) viscous heating or chemical reaction.
d) both (b) and (c).
d) both (b) and (c).
125
A __________ surface has the maximum thermal emissivity out of the following.
a) black & smooth
b) black & rough
c) white & smooth
d) white & rough
b) black & 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
b) d
c) d^2
d) d^1.5
c) d^2
127
Mechanical recompression evaporation is used in the production of
a) alcohol
b) distilled water
c) salt
d) fruits jam
b) 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 __________ number.
a) Condensation
b) Grashoff
c) Stantan
d) Brinkman
d) Brinkman
129
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
d) arrest the entrained liquid
130
What is the thermal conductivity of a perfect heat insulator ?
a) zero
b) one
c) ∞
d) between 0 and ∞
a) zero
131
'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.
b) factor of safety.
132
A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter 'd'. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to
a) d^0.8
b) d^-0.2
c) d^-1
d) d^-1.8
b) d^-0.2
133
Prandtl and Reynolds analogy are same, when Prandtl number is
a) 0.5
b) 1
c) > 2
d) 1.5
b) 1
134
Heat transfer occurs by natural convection because change in temperature causes difference in
a) viscosity
b) density
c) thermal conductivity
d) heat capacity
b) density
135
The critical radius 'r' of insulation on a pipe is given by
a) r = 2k/h
b) r = k/h
c) r = k/2h
d) r = h/k
b) r = k/h
136
As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the
a) temperature of the body only.
b) wavelength of monochromatic radiation.
c) both (a) and (b).
d) nature of material of body.
a) temperature of the body only.
137
If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid
a) remains unchanged.
b) increases.
c) increases or decreases depending on number of shell passes.
d) decreases.
d) decreases.
138
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.
b) painting the surface white (with aluminium paint).
139
__________ paint has the maximum absorption coefficient.
a) Black
b) Yellow
c) White
d) Grey
a) Black
140
