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DAY 2 > Heat Transfer Part 3 > Flashcards

Heat Transfer Part 3 Flashcards

1
Q

In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid
varies directly as the area and the LMTD.
directly proportional to LMTD and inversely proportional to the area.
varies as square of the area.
none of these.

A

varies directly as the area and the LMTD.

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2
Q

With increase in temperature, the total emissivity of conductors
increases
decreases
remains same
decreases linearly

A

increases

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3
Q

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

A

all (a), (b) & (c)

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4
Q

Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator.
long tube
falling film
high pressure
none of these

A

falling film

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5
Q

Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping
both the tube sheets fixed.
both the tube sheets floating.
the top tube sheet floating and bottom tube sheet fixed.
the top tube sheet fixed and the bottom tube-sheet floating.

A

both the tube sheets fixed.

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6
Q

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
2
2^0.8
2^0.2
2^0.5

A

2^0.8

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7
Q

Heat sensitive materials can be concentrated in an evaporator employing
vacuum
high pressure
high residence time
none of these

A

vacuum

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8
Q

A concentric double pipe heat exchanger as compared to the shell and tube heat exchanger for the same heat load requires
less heating surface.
more space.
lower maintenance cost.
none of these.

A

more space.

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9
Q

In a shell and tube heat exchanger, floating head is used for
large temperature differentials.
high heat transfer co-efficient.
low pressure drop.
less corrosion of tubes.

A

large temperature differentials.

floating head large temp differentials

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10
Q

Steam trap is used to
condense the steam flowing in the pipeline.
remove water resulting from partial condensation of steam.
stop the supply of steam.
none of these.

A

remove water resulting from partial condensation of steam.

Stream trap remove water

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11
Q

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
ha = 0.8hL
ha = 2hL
ha = hL
ha = 5hL

A

ha = 2hL

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12
Q

What is the logarithmic mean of r1 and r2 ?
(r1-r2/ln(r1/r2))
(r1-r2/ln(r2/r1))
(r2-r1/ln(r1/r2))
(r1-r2/-ln(r1/r2))

A

(r1-r2/ln(r1/r2))

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13
Q

Maximum heat transfer rate is achieved in __________ flow.
co-current
counter-current
turbulent
laminar

A

turbulent

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14
Q

Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law.
Stefan’s
Dalton’s
Wien’s
Kirchoffs

A

Wien’s

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15
Q

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.
40
95
70
50

A

70

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16
Q

Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger?
Corrosiveness & fouling characteristics
pressure
viscosity
density

A

density

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17
Q

Corrosiveness of steam condensate is due to the presence of
CO2
dissolved O2
both (a) & (b)
neither (a) nor (b)

A

both (a) & (b)

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18
Q

The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy.
Colburn
Reynolds
Prandtl
none of these.

A

Colburn

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19
Q

The driving potential for the crystal growth during crystallisation is the __________ of the solution.
concentration
viscosity
super-saturation
density

A

super-saturation

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20
Q

jH factor for heat transfer depends upon the __________ number.
Biot
Nusselt
Reynolds
Prandtl

A

Reynolds

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21
Q

Kg of liquid evaporated per hour in an evaporator is defined as its
capacity
economy
steam load
none of these

A

capacity

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22
Q

Pick out the correct statement.
1 kcal/hr.m. C is equal to 1 BTU/hr. ft. F.
In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity.
In unsteady state heat conduction, heat flows in the direction of temperature rise.
In heat transfer by forced convection, Grashoff number is very important.

A

In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity.

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23
Q

Open pan evaporators are preferred to be used, when the solution to be concentrated is
scaling
highly viscous
corrosive
salty

A

highly viscous

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24
Q

Cp.μ/K is termed as the __________ number.
Grashoff
Nusselt
Prandtl
Stanton

A

Prandtl

PrCpuK Prandtl Cpu/K

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25
Q

The maximum heat transfer co-efficient from steam heating will be attained when the steam is
supersaturated
saturated
wet
none of these

A

saturated

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26
Q

Kirchoff’s law is applicable to
monochromatic radiation only
total radiation only
both (a) and (b)
only volumes and not to surfaces

A

both (a) and (b)

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27
Q

In a forward feed multiple effect evaporator, the pressure is
highest in last effect
lowest in last effect
same in all effects
dependent on the number of effects

A

lowest in last effect

foward feed - pressure lowest in last effect

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28
Q

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
increase
decrease
remain unchanged
either increase or decrease; depends on the coolant flow rate

A

remain unchanged

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29
Q

Which of the following situations can be approximated to a steady state heat transfer system?
A red hot steel slab (having outside surface temperature as 1300 C) exposed to the atmosheric air at 35 C.
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.
Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180 C.
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.

A

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.

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30
Q

Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212 F may be around __________ BTU.
180
970
3.97
data insufficient, can’t be predicted

A

180

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31
Q

The unit of conductance in SI unit is
W/m
W/m2
W/ K
W/m K

A

W/ K

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32
Q

In a shell and tube heat exchanger, square pitch compared to triangular pitch
gives a higher shell side pressure drop.
gives a lower shell side pressure drop.
can pack more surface area into a shell of given diameter.
none of these.

A

gives a higher shell side pressure drop.

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33
Q

Which of the following has maximum thermal conductivity?
Iron
Coal
Nitrogen
Tar

A

Iron

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34
Q

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.
6
12
18
24

A

12

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35
Q

The film co-efficient between condensing vapour and metal wall increases with
increasing temperature of the vapour.
decreasing temperature of the vapour.
increasing viscosity of the film of condensate.
increasing temperature drop.

A

increasing temperature of the vapour.

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36
Q

Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.
Grashoff
Reynolds
both ‘a’ & ‘b’
Prandtl & Grashoff

A

Prandtl & Grashoff

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37
Q

The thermal boundary layer at NPr > 1
is thicker than hydrodynamic boundary layer.
is thinner than hydrodynamic boundary layer.
and the hydrodynamic boundary layer are identical.
disappears.

A

is thinner than hydrodynamic boundary layer.

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38
Q

In the free convection regime of pool boiling, the heat flux is proportional to
Δt^1/2
Δt^2
Δt^5/4
Δt

A

Δt^5/4

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39
Q

With increase in temperature, the thermal conductivity of fresh lubricating oil
increases
decreases
remains unchanged
may increase or decrease; depends on its composition

A

decreases

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40
Q

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
0.4
0.5
0.6
0.7

A

0.7

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41
Q

Nusselt number is the ratio of the temperature gradient at the wall to
temperature difference
heat flux
that across the entire pipe
none of these

A

that across the entire pipe

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42
Q

The Stefan-Boltzman constant depends on the
medium
temperature
surface
none of these

A

none of these

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43
Q

The units of resistance to heat transfer is
J.m-2.K-1
J.m-1.K-1
W.m-2.K-1
W-1m2K

A

W-1m2K

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44
Q

Thermal conductivity of a gas at low density, __________ with increase in temperature.
decreases
increases
remains unchanged
may increase or decrease; depends on the gas

A

increases

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45
Q

Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.
Grashoff
Biot
Stantan
Reynolds

A

Grashoff

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46
Q

__________ heat exchanger is used for chilling oil to be dewaxed.
U-tube
Double pipe
Fixed tube
Floating head

A

Double pipe

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47
Q

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
> 0.75
< 0.75
< 0.50
< 0.25

A

< 0.75

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48
Q

Pick out the wrong statement.
Economy of a multiple effect evaporator is not influenced by the boiling point elevation.
Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature.
Double pipe heat exchangers are mostly used in the field of refrigeration.
Finned tube heat exchangers are suitable for heating air by steam.

A

Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature.

wrong two identical cubes

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49
Q

In sub-cooled boiling,
temperature of the heating surface is less than the boiling point of the liquid.
temperature of the heating surface is more than the boiling point of the liquid.
bubbles from heating surface are absorbed by the mass of the liquid.
very large vapour space is necessary.

A

temperature of the heating surface is more than the boiling point of the liquid.

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50
Q

With increase in temperature, the thermal conductivity of a gas
increases.
decreases.
remains same.
may increase or decrease depending on the type of gas.

A

increases.

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51
Q

A __________ evaporator employs an annular downtake.
basket type
horizontal
long tube vertical
none of these

A

basket type

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52
Q

Radiation heat losses from satisfactorily insulated high pressure boilar may be about __________ percent.
1
7
18
26

A

7

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53
Q

In natural convection heat transfer, the correlating parameter is the
Graetz number
Eckert number
Grashoff number
Bond number

A

Grashoff number

54
Q

Boiling of milk in an open vessel is an example of __________ boiling.
film
sub-cooled
saturated nucleate
none of these

A

film

55
Q

Pick out the wrong statement.
In process heat exchangers, saturated steam is preferred over the superheated steam.
The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of lamda1. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 lamda1.
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.
A body at 925 K emits an energy of 1.42 x 1011oW/m2 (o is the Stefan-Boltzman constant) in the wavelength band between 3 um to 4 um. The fraction of this energy in the total energy emitted over the entire wavelength range is equal to emissivity.

A

The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of lamda1. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 lamda1.

56
Q

Mode of heat transfer involved in the cooling of air cooled internal combustion engine is
conduction
natural convection
forced convection
none of these

A

natural convection

57
Q

Steady state one dimensional heat flow by conduction as given by Fourier’s low does not assume that
there is no internal heat generation.
boundary surfaces are isothermal.
material is anisotropic.
constant temperature gradient exists.

A

material is anisotropic.

does not assume anistropic

58
Q

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
77.2
71.2
63.8
48.7

A

48.7

59
Q

In a shell and tube heat exchanger, the shell side fluid velocity can not be changed by changing the
tube layout
tube diameter
tube pitch
no. of baffles

A

tube diameter

60
Q

To reduce the tube side pressure drop for the same flow rate, the heat exchanger recomended is
1-2 heat exchanger
1-1 heat exchanger
3-2 heat exchanger
2-4 heat exchanger

A

1-1 heat exchanger

61
Q

Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by
This is valid for the value of NRe equal to
< 2100
2100-4000
> 4000
> 10000

A

> 10000

62
Q

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2 C.
10-50
100-500
1000-1500
5000-15000

A

5000-15000

63
Q

Correction is applied to LMTD for __________ flow.
parallel
counter
cross
none of these

A

cross

64
Q

If h1 = inner film co-efficient and /h2 = outer film co-efficient, then the overall heat transfer co-efficient is
always less than h1
always between h1 and h2
always higher than h2
dependent on metal resistance

A

always between h1 and h2

65
Q

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
heat the water from 0 C to 100 C.
evaporate the water.
to superheat the steam.
data insufficient, can’t be predicted

A

evaporate the water.

evaporate water - 1 kg H2O to superheated major consumption

66
Q

For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.
extremely low
low
high
no

A

high

67
Q

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
11.2 kW/m2
12.0 kW/m2
14.6 kW/m2
16.5 kW/m2

A

16.5 kW/m2

68
Q

Heat exchangers operating, when the asymptotic range is reached,
provide very large heat transfer co-efficient.
results in making part of the heating surface inactive.
results in abruptly increased velocity.
none of these

A

results in making part of the heating surface inactive.

69
Q

In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell)
D/5 and D
D/2 and 2 D
D/4 and 2 D
D and 2 D

A

D/5 and D

70
Q

In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.
geometric
arithmetic
logarithmic
either (a), (b) or (c)

A

logarithmic

71
Q

In a gas-liquid shell and tube heat exchanger, the
presence of a non-condensible gas decreases the condensing film co-efficient.
gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature.
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.
all ‘a’, ‘b’ & ‘c’

A

all ‘a’, ‘b’ & ‘c’

gas-liquid STHE all a, b & c

72
Q

Which is the most suitable for the concentration of foamy & frothy liquors?
Agitated film evaporator
Long tube vertical evaporator
Open pan evaporator
None of these

A

Long tube vertical evaporator

73
Q

Boiling point elevation of an ideal solution
increases rapidly with temperature rise.
decreases rapidly with temperature rise
in independent of pressure.
both (b) and (c).

A

increases rapidly with temperature rise.

74
Q

The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the
heating volume
heat transfer area
Nusselt number
none of these

A

heat transfer area

75
Q

Which of the following has the lowest overall heat transfer co-efficient?
Downtherm
Molten sodium
Water
Air

A

Air

76
Q

Which of the following has the minimum absorptivity?
Aluminum foil
Coal dust
Refractory bricks
Iron plates

A

Aluminum foil

77
Q

A black body when hot, emits heat radiation of __________ wavelengths.
small
large
all
one fixed

A

all

78
Q

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
CPA > CPB
CPA < CPB
kA < 0.5kB
kA>2 kB

A

kA < 0.5kB

79
Q

Vibrations in the tubes of a shell and tube heat exchanger is induced due to the
flow of fluid on the tube and shell sides.
oscillations in the flow of shell/tube sides fluid.
vibrations transmitted through piping and/or supports due to external reasons.
all (a), (b) and (c)

A

all (a), (b) and (c)

80
Q

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
0.2
0.4
0.6
0.8

A

0.6

81
Q

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
1.66
88.86
3.66
dependent on NRe only

A

3.66

82
Q

Sensible heat of hot industrial flue gases can not be recovered by a/an
economiser
regenerator
ceramic recuperator
none of these

A

none of these

83
Q

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)
K/h0
2K/h0
h0/K
h0/2K

A

2K/h0

84
Q

Radiator of an automobile engine is a __________ type of heat exchanger.
co-current
cross-current
counter-current
direct contact

A

direct contact

85
Q

In pipe flow, heat is transferred from hot wall to the liquid by
conduction only
forced convection only
forced convection and conduction
free and forced convection

A

forced convection and conduction

86
Q

The value of Stefan-Boltazman constant in SI unit is
5.6697 x 10-8W/m2. K4
0.1714 x 10-8W/m2. K4
5.6697 x 10-8kcal/m2 . K4
0.1714 x 10-8kcal/m2. K4

A

5.6697 x 10-8W/m2. K4

87
Q

The unit of heat transfer co-efficient is
BTU/hr. ft2 F
BTU/hr. F. ft.
BTU/hr. F
BTU/hr. ft

A

BTU/hr. ft2 F

88
Q

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
1
1.74
6.1
37

A

6.1

Dittus-Boelter halved doubled 6.1

89
Q

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
165.4
167.5
172.5
175

A

165.4

90
Q

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
0.5
2
10
100

A

2

91
Q

Low thermal conductivity of heat insulating materials is due to its
dense structure
high proportion of air space
high specific heat
none of these

A

high proportion of air space

92
Q

The most conducive surface for dropwise condensation to occur is the __________ surface.
coated
oily
glazed & polished
smooth

A

oily

DO dropwise oily

93
Q

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
concentrations
chemical potentials
activity co-efficients
mass transfer co-efficients

A

concentrations

94
Q

Calburn analogy is applicable for the value of Prandtl number from
0.001 to 1
0.6 to 120
0.5 to 5
120 to 400

A

0.6 to 120

95
Q

Pick out the correct equation.
jH = (St)(Pr)^2/3 = f/2
jH = (St)(Pr)^1/3 = f/2
jH = (St)^2/3(Pr) = f/2
jH = (St)^1/3(Pr) = f/2

A

jH = (St)(Pr)^2/3 = f/2

96
Q

Multiple effect evaporators ar used to
increase the steam economy & decrease the capacity.
increase the steam economy & the capacity.
decrease the steam economy & the capacity.
decrease the steam economy & increase the capacity.

A

increase the steam economy & the capacity.

97
Q

Prandtl number is given by
(Cpu)/a
hD/k
(Cpu)/k
?/(h*Cp)

A

(Cp*u)/k

98
Q

Small scale evaporation is done in a
heat exchanger
condenser
multiple effect evaporator
steam jacketed kettle

A

steam jacketed kettle

99
Q

Heat exchanger tubes are never made of
plain carbon steel
stainless steel
lead
copper

A

lead

100
Q

At constant temperature, the thermal conductivities of gases __________ with rise in pressure.
decrease
increase
remain unchanged
may increase or decrease; depends on the pressure

A

decrease

101
Q

Reason for operating an evaporator in multiple effect is to secure
increased steam economy.
decreased steam consumption.
both (a) and (b).
increased capacity.

A

both (a) and (b).

102
Q

In a cooling tower, water becomes cool by
loosing sensible heat.
heat transfer to surroundings.
vaporisation due to heat loss to air.
loosing latent heat.

A

loosing sensible heat.

103
Q

In Fourier’s law, the proportionality constant is called the
heat transfer co-efficient
thermal diffusivity
thermal conductivity
Stefan-Boltzman constant

A

thermal conductivity

104
Q

The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation.
greater than
lower than
is same as
half

A

lower than

105
Q

Pick out the wrong statement.
Bubble size increases with the dynamic viscosity of the liquid in case of nucleate pool boiling.
Thermal conductivity of a dry material is more than that of the damp material.
Ratio of its capacity to economy equals the steam consumption in kg/hr in an evaporator.
Vaporisation of organic substances in evaporator mostly causes foam formation.

A

Thermal conductivity of a dry material is more than that of the damp material.

106
Q

Duhring’s plot’ is of use in
extractive distillation
evaporation
leaching
absorption

A

evaporation

107
Q

Which has the lowest Prandtl number?
Liquid metal
Aqueous solution
Water
Lube oil

A

Liquid metal

108
Q

Pick out the wrong statement.
The value of hydrostatic head increases with increase in vacuum in the effect in a multiple effect evaporator system.
Entering velocity of the liquid in the tubes of natural circulation evaporators is in the range of 0.3 to 0.9 metre/second.
Duhring’s plot is used for calculating the concentration of solution.
In a multiple effect evaporation system, the number of effects is limited by the total boiling point rise.

A

Duhring’s plot is used for calculating the concentration of solution.

109
Q

Prandtl number for most of dry gases is about
0.001
0.72
70
150

A

0.72

110
Q

Prandtl number is the reciprocal of
Thermal diffusivity/Momentum diffusivity
thermal diffusivity x Momentum
Thermal diffusivity x Mass diffusivity
Mass diffusivity x Momentum diffusivity

A

Thermal diffusivity/Momentum diffusivity

111
Q

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
less than 45 C
more than 45 C
equal to 45 C
initially decreases and remains constant thereafter.

A

more than 45 C

112
Q

For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is
Nu = 0.023 Re^0.8 . Pr^0.4
Nu = pi/2 x Gz
Nu = 2/pi x Gz
Nu = 2Gz^0.5

A

Nu = 2/pi x Gz

113
Q

Multiple effect evaporation accounts for
steam economy
lower operating costs
investment economy
none of these

A

steam economy

114
Q

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
more
less
same
more or less; depends on the nature of solution

A

more

115
Q

Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around __________ metres/second.
1
10
20
30

A

1

116
Q

In Biot number, the characteristic length used is the ratio of the __________ of the solid.
volume to surface area
perimeter to surface area
surface area to volume
surface area to perimeter

A

volume to surface area

BVS Biot Volume to Surface

117
Q

Which of the following is the most widely used heat insulating material for pipelines carrying steam?
Tar dolomite bricks followed by asbestos.
Fireclay refractory followed by aluminium sheet.
Cotton followed by aluminium foil.
85% magnesia cement and glass wool.

A

85% magnesia cement and glass wool.

118
Q

Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re^0.8 . Pr^n, is not valid, if the value of
n = 0.4 is used for heating.
n = 0.3 is used for cooling.
Reynolds number for the flow involved is > 10000.
Reynolds number for the flow involved is < 2100.

A

Reynolds number for the flow involved is < 2100.

119
Q

Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling?
Square pitch
Triangular pitch
Diagonal square pitch
None of these

A

Triangular pitch

120
Q

In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid
is inversely proportional to the resistance across which the drop occurs.
and the wall are proportional to individual resistances.
and the wall is not related.
none of these.

A

and the wall are proportional to individual resistances.

121
Q

The purpose of providing expansion bellows in the shell of tubular exchanger is to
increase the heating load.
impart structural strength.
account for the uneven expansion of shell and tube bundles.
facilitate increase of shell length, if needed.

A

account for the uneven expansion of shell and tube bundles.

122
Q

A graph between __________ is called Wilson plot.
1/U Vs. 1/V^0.8
1/(V^0.8) Vs. U
V^0.8 Vs. U
1/U vs. 1/V

A

1/U Vs. 1/V^0.8

123
Q

Grashhoff number is given by
gD³.β.Δtρ²/μ²
gD²βΔtρ/μ²
gD²βΔtP²μ
gD³βΔtP²/μ

A

gD³.β.Δtρ²/μ²

Grashhoff D³ ρ²

124
Q

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
1200W/m2.K
894W/m2.K
333W/m2.K
287 W/m2.K

A

333W/m2.K

125
Q

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
2000
4000
5000
6000

A

5000

126
Q

Pick out the wrong statement.
Solvates’ are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a ‘hydrate’.
In heat exchanger calculations (?t)weighted is used in place of ?t, when it involves more than one sequence of heating or cooling i.e., desuperheating & condensation or condensation & sub-cooling.
Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted.
In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area.

A

Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted.

wrong - not influence by agitation

127
Q

What is the geometric mean of two heat transfer areas A1 and A2?
√(A₁ * A₂)
√(A₁ + A₂)
1/2 √(A₁ * A₂)
2 √(A₁ * A₂)

A

√(A₁ * A₂)

128
Q

Evaporation by thermocompression results in the
saving of steam.
realisation of multiple effect economy in a single effect.
both (a) and (b).
none of these.

A

both (a) and (b).

129
Q

Forced circulation evaporators are normally used for concentrating liquids having
scaling characteristics
high viscosity
both(a) & (b)
neither (a) nor (b)

A

both(a) & (b)

130
Q

Steam economy in case of a triple effect evaporator will be
1
< 1
> 1
between 0 and 1

A

> 1

DAY 2 (23 decks)

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