IBX - Heat Transfer Sec. 1 to 6

Question 1

Crystal size in a continuous crystalliser depends upon the

rate of heat transfer.
degree of turbulence.
degree of supersaturation.
all (a), (b) and (c).

Answer 1

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

Question 2

Heat waves

can not pass through vacuum.
travel in straight line.
can be reflected by a mirror.
both (b) and (c).

Answer 2

both (b) and (c).

Question 3

Air is best heated with steam in a heat exchanger of

plate type.
double pipe type with fin on steam side.
double pipe type with fin on air side.
shell and tube type.

Answer 3

double pipe type with fin on air side.

Question 4

Which of the following is generally considered as opaque surface towards radiations?

Gases
Solids
Liquids
Both (b) and (c)

Answer 4

Both (b) and (c)

Question 5

Black liquor generated during paper manufacture is concentrated in a

single effect evaporator.
single effect evaporator followed by a crystalliser.
multiple effect evaporator.
multiple effect evaporators followed by a crystalliser.

Answer 5

multiple effect evaporator.

Question 6

When vaporisation takes place directly at the heating surface, it is called

film boiling
nucleate boiling
vapour binding
none of these

Answer 6

nucleate boiling

Question 7

Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively)

C/E
E/C
CE
1/CE

Answer 7

C/E

Question 8

Reynold’s analogy states that

Nst α f
Nst α NRe
NNu α f
NRe α f

Answer 8

Nst α f

Question 9

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

decreases
increases
remains constant
first decreases upto certain temperature and then increases

Answer 9

increases

Question 10

Fourier’s law applies to the heat transfer by

convection
radiation
conduction
all (a), (b) & (c)

Answer 10

conduction

Question 11

Shell side pressure drop in a shell and tube heat exchanger does not depend upon the

baffle spacing & shell diameter.
tube diameter & pitch.
viscosity, density & mass velocity of shell side fluid.
none of these.

Answer 11

none of these.

Question 12

In the equation Q = UAΔt; Δt is

geometric mean temperature difference.
arithmetic mean temperature difference.
logarithmic mean temperature difference.
the difference of average bulk temperatures of hot and cold fluids

Answer 12

logarithmic mean temperature difference.

Question 13

With increase in porosity, the thermal conductivity of a solid substance

increases
decreases
remains unchanged
may increase or decrease; depends on the soli

Answer 13

decreases

Question 14

For an ideal black body

absorptivity = 1
reflectivity = 1
emissivity = 0
transmissivity = 1

Answer 14

absorptivity = 1

Question 15

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

40.5
34.4
26.8
25

Answer 15

34.4

Question 16

Fouling factor

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

Answer 16

accounts for additional resistances to heat flow.

Question 17

In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient

increases
decreases
is not affected
may increase or decrease; depends on the feed

Answer 17

decreases

Question 18

The steam ejector is used to

remove condensate from the steam pipelines.
create vacuum.
superheat the steam.
none of these.

Answer 18

create vacuum.

Question 19

For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area

increases
decreases
remains constant
passes through a maxima

Answer 19

passes through a maxima

Question 20

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

(COP)R = (COP)HP = 0.6
(COP)R = 2.5; (COP)HP = 1.5
(COP)R = 1.5; (COP)HP = 2.5
(COP)R = (COP)HP = 2.5

Answer 20

(COP)R = 1.5; (COP)HP = 2.5

Question 21

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

32
37
45
50

Answer 21

32

Question 22

In a heat exchanger, floating head is provided to

facilitate cleaning of the exchanger.
increase the heat transfer area.
relieve stresses caused by thermal expansion.
increase log mean temperature gradient.

Answer 22

relieve stresses caused by thermal expansion.

Question 23

Leidenfrost point is a term concerned with the

condensation of the saturated vapor on a cold surface.
concentration of a corrosive solution by evaporation.
heat transfer between two highly viscous liquids.
boiling of a liquid on a hot surface.

Answer 23

boiling of a liquid on a hot surface.

Question 24

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

counter flow with process stream on shell side.
counter flow with process stream on tube side.
parallel flow with process stream on shell side.
parallel flow with process stream on tube side.

Answer 24

counter flow with process stream on shell side.

Question 25

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

Answer 25

I^2R

Question 26

Pick out the wrong statement.

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

Answer 26

Orifice baffles are never used in a shell and tube heat exchanger.

Question 27

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.

laminar
transition
both ‘a’ & ‘b’
highly turbulent

Answer 27

highly turbulent

Question 28

The actual temperature drop across the heating surface in an evaporator depends on the

feed.
depth of liquid over heating surface.
pressure difference between steam chest and vapour space.
all (a), (b) and (c).

Answer 28

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

Question 29

Which of the following is not used as a medium for high temperature heating?

Dowtherm
mercury
liquid metal (e.g. molten sodium)
fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)

Answer 29

mercury

Question 30

Presence of a non-condensing gas in a condensing vapour

increases the rate of condensation.
decreases thermal resistance.
is desirable to increase the film co-efficient.
none of these.

Answer 30

none of these.

Question 31

Kirchoff s law applies to __________ radiation.

total
monochromatic
both (a) & (b)
neither (a) nor (b)

Answer 31

both (a) & (b)

Question 32

With the increase of temperature, the Col-burn jH factor

increases.
decreases.
remains unchanged.
may increase or decrease ; depending on temperature.

Answer 32

increases.

Question 33

In case of evaporators, liquid entrainment results primarily due to

high vacuum in the evaporator.
high evaporation rate.
foaming of the solution.
high heat transfer rate.

Answer 33

foaming of the solution.

Question 34

Baffles in the shell side of a shell and tube heat exchanger

increase the cross-section of the shell side liquid.
force the liquid to flow parallel to the bank.
increase the shell side heat transfer co-efficient.
decrease the shell side heat transfer co-efficient.

Answer 34

increase the shell side heat transfer co-efficient.

Question 35

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

finned tube heat exchanger with air inside and steam outside.
finned tube heat exchanger with air outside and steam inside.
shell and tube heat exchanger with air inside tubes and steam on shell side.
shell and tube heat exchanger with air on shell side and steam inside tubes.

Answer 35

finned tube heat exchanger with air outside and steam inside.

Question 36

The unit of heat transfer co-efficient in SI unit is

J/M2°K
W/m2°K
W/m°K
J/m°K

Answer 36

W/m2°K

Question 37

The number of kg vaporised per kg of steam fed to the evaporator is defined as

capacity
rate of evaporation
economy
rate of vaporisation

Answer 37

economy

Question 38

Pick out the wrong statement.

In case of heat transfer by purely forced convection, GR/Re^2 ≤ 1.
The equivalent diameter of heat transfer for a duct of square cross-section (having each side as ‘x’) is equal to 4x.
Distillation process is not the same as evaporation.
The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface.

Answer 38

The equivalent diameter of heat transfer for a duct of square cross-section (having each side as ‘x’) is equal to 4x.

Question 39

Economy of a multiple effect evaporator is not influenced much by the

boiling point elevations
temperature of the feed
rate of heat transfer
ratio of the weight of the thin liquor to thick liquor

Answer 39

boiling point elevations

Question 40

Increasing the liquor level in the evaporator results in the

decreased capacity.
increase in liquor film co-efficient.
decreased effect of hydrostatic head.
increased true temperature drop.

Answer 40

decreased capacity.

Question 41

The equivalent diameter for pressure drop is __________ that for heat transfer.

smaller than
greater than
equal to
not related with

Answer 41

smaller than

Question 42

Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer.

no
the least
the largest
lower

Answer 42

the largest

Question 43

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

25°C
30°C
35°C
40°C

Answer 43

35°C

Question 44

Thermal conductivity of a conducting solid material depends upon its

temperature
porosity
both (a) & (b)
neither (a) nor (b)

Answer 44

both (a) & (b)

Question 45

Pick out the wrong statement.

The controlling resistance in case of heating of air by condensing steam is in the air film.
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.
In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs.
Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature.

Answer 45

In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs.

Question 46

The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film )

(ΔT)^2
sqrt(ΔT)
(ΔT)^1/4
(ΔT)^3/2

Answer 46

(ΔT)^1/4

Question 47

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is

in the central core of the fluid.
uniformly distributed throughout the fluid.
mainly confined to a thin film of fluid near the surface.
none of these.

Answer 47

mainly confined to a thin film of fluid near the surface.

Question 48

Which of the following is concerned with both heat and mass transfer?

Lewis relationship
Nusselt number
Kutateladze number
Froude number

Answer 48

Lewis relationship

Question 49

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

higher economy
lower capacity
both (a) & (b)
lower economy

Answer 49

higher economy

Question 50

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

greater than that for uninsulated steam pipe.
less than that of the uninsulated steam pipe.
equal to that of the uninsulated steam pipe.
less than the steam pipe with 5 cms insulation.

Answer 50

less than that of the uninsulated steam pipe.

Question 51

Which area is used in case of heat flow by conduction through a cylinder?

Logarithmic mean area
Arithmetic mean area
Geometric mean area
None of these

Answer 51

Logarithmic mean area

Question 52

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

between two bodies in physical contact with each other.
between two bodies not in physical contact with each other.
from one part of a body to the another part of the same body.
both ‘b’ & ‘c’

Answer 52

between two bodies not in physical contact with each other.

Question 53

The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is

Nusselt number.
Sherwood number.
Schmidt number.
Stanton number.

Answer 53

Schmidt number.

Question 54

Finned tube heat exchangers

give larger area per tube.
use metal fins of low thermal conductivity.
facilitate very large temperature drop through tube wall.
are used for smaller heat load

Answer 54

give larger area per tube.

Question 55

The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation.

increases
decreases
remains constant
may increase or decrease ; depends on the material

Answer 55

may increase or decrease ; depends on the material

Question 56

Which one gives the monochromatic emissive power for black body radiation ?

Planck’s law
Kirchhoffs law
Wien’s law
Stefan-Boltzman law

Answer 56

Planck’s law

Question 57

For what value of Prandtl number, St = f/2?

1.5
1
> 1
< 1

Answer 57

1

Question 58

In a shell and tube heat exchanger,

the temperature drops in the two fluids and the wall are proportional to individual resistances.
the temperature drop is inversely proportional to the resistance across which the drop occurs.
there is no relationship between temperature drop and resistance.
the relationship is not generalised.

Answer 58

the temperature drops in the two fluids and the wall are proportional to individual resistances.

Question 59

Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid

for fluids in laminar flow.
for fluids in turbulent flow.
when Grashhoff number is very important.
for liquid metals.

Answer 59

for fluids in turbulent flow.

Question 60

The equation, Nst = (f/2)/[1+5(NPr-1)sqrt(f/2)] , corrosponds to __________ analogy.

Von-Karmann
Reynolds
Colburn
Prandtl

Answer 60

Prandtl

Question 61

For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it

occupies smaller space.
is more economical.
is easy to operate and maintain.
all (a), (b) and (c).

Answer 61

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

Question 62

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?

Constant overall heat transfer coefficient.
Constant rate of fluid flow.
Constant specific heat.
No partial phase change in the system.

Answer 62

Constant rate of fluid flow.

Question 63

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

convection becomes important
conduction becomes important
radiation becomes important
sub-cooled boiling occurs

Answer 63

radiation becomes important

Question 64

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.)

t
1/ρ
1/A
all (a), (b) & (c)

Answer 64

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

Question 65

Temperature profile in steady state heat transfer is

asymptotic
hyperbolic
parabolic
linear

Answer 65

linear

Question 66

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

decreases the pressure drop.
decreases the outlet temperature of cooling medium.
increases the overall heat transfer coefficient.
none of these.

Answer 66

increases the overall heat transfer coefficient.

Question 67

When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.

pool
nucleate
transition
film

Answer 67

film

Question 68

Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter)

0.2 D
0.5 D
0.66 D
0.80 D

Answer 68

0.2 D

Question 69

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 )
t^4
T^4
1/t^4
1/T^4

Answer 69

T^4

Question 70

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is

2.36
4.36
120.36
dependent on NRe only

Answer 70

4.36

Question 71

What is the unit of thermal conductivity ?

Kcal/hr. m2 °C
Kcal/hr.m.°C
Kcal/hr.m
Kcal/hr. °C

Answer 71

Kcal/hr.m.°C

Question 72

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

black painted bodies only
all bodies
polished bodies only
a black body

Answer 72

all bodies

Question 73

It is not preferable to use superheated steam in evaporators, because of its very

high temperature
high pressure
low film co-efficient
none of these

Answer 73

low film co-efficient

Question 74

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

3.06 x 10^5
6.12 x 10^5
7.24 x 10^5
9.08 x 10^5

Answer 74

3.06 x 10^5

Question 75

LMTD for counterflow and prallel flow heat exchanger will be the same, when the

cold fluid is heated to a certain temperature by condensing steam (isothermal fluid).
outlent temperature of both the hot and cold fluid are same.
outlet temperature of hot fluid is less than the outlet temperature of the cold fluid.
none of these.

Answer 75

cold fluid is heated to a certain temperature by condensing steam (isothermal fluid).

Question 76

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)
NPr
NPr^1/3
NPr^-1
NPr^-1/3

Answer 76

NPr^1/3

Question 77

The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns.

0.38-0.78
0.5-50
100-1000
5-50

Answer 77

0.5-50

Question 78

Use of transverse baffles in a shell and tube heat exchanger is done to increase the

rate of heat transfer.
flow velocity.
turbulence of shell side fluid.
all (a), (b) and (c).

Answer 78

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

Question 79

The actual temperature drop across the heating surface of an evaporator depends on the

liquid depth over the heating surface.
solution being evaporated.
pressure difference between the steam chest and the vapor space above the boiling liquid.
all (a), (b) and (c)

Answer 79

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

Question 80

Economy of a multiple effect evaporator depends upon the

heat balance consideration
rate of heat transfer
both (a) and (b)
neither (a) nor (b)

Answer 80

heat balance consideration

Question 81

The Graetz number is concerned with the

mass transfer between a gas and a liquid.
absorption with chemical reaction.
heat transfer in turbulent flow.
heat transfer in laminar flow.

Answer 81

heat transfer in laminar flow.

Question 82

Solid angle subtended by the finite surface at the radiating element is

called the view factor.
called the angle of vision.
proportional to the square of the distance between surfaces.
expressed in terms of radians.

Answer 82

called the angle of vision.

Question 83

Pick out the wrong statement.

The emissivity of a surface decreases, if it gets corroded by atmospheric environment.
The emissivity of a surface increases with increase in surface roughness.
The emissivity of a polished surface is quite low.
The emissivity of a non-metallic surface decreases with increase in the temperature.

Answer 83

The emissivity of a surface decreases, if it gets corroded by atmospheric environment.

Question 84

In forced convection, the heat transfer depends on

Re, Pr
Re, Gr
mainly Gr
Re only

Answer 84

Re, Pr

Question 85

With increase in temperature, the thermal conductivity of most liquids

increases
decreases
remains same
first increases upto a certain temperature and then becomes constant

Answer 85

decreases

Question 86

Heat transfer by __________ may not necessarily require the presence of a medium.

conduction
natural convection
forced convection
radiation

Answer 86

radiation

Question 87

Pick out the correct statement.

Higher is the temperature of the radiating body, higher is the wavelength of radiation.
Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder.
The wavelength corresponding to maximum mono-chromatic emissive power increases with rise in temperature.
Solid angle subtended by the finite surface at the radiating element is called the angle of incidence.

Answer 87

Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder.

Question 88

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.

Answer 88

in high range of temperature differences.

Question 89

Stefan-Boltzman law applies to __________ body.

black
white
grey
any colour

Answer 89

black

Question 90

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

more
less
some
either more or less ; depends on the nature of vapor

Answer 90

some

Question 91

A perfect black body is a perfect __________ of radiation.

absorber
emitter
both (a) & (b)
neither (a) nor (b)

Answer 91

both (a) & (b)

Question 92

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
more than
less than
either more or less than (depending upon the fluid)

Answer 92

equal to

Question 93

An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporisation of another, is called a

boiler
heat exchanger
recuperator
regenerator

Answer 93

heat exchanger

Question 94

Which of the following is directly concerned with the heat transfer?

Strouhal number
Sherwood number
Euler number
Grashoff number

Answer 94

Grashoff number

Question 95

Pick out the wrong statement:

With change in temperature, the radiant energy emitted by a black body remains unchanged.
Absorptivity of a body approaches unity in case of diffuse reflection.
Absorptivity of a perfectly black body is unity.
Value of Stefan-Boltzman constant is 4.876 x 10-8 KCal/m2.hr.°K4.

Answer 95

With change in temperature, the radiant energy emitted by a black body remains unchanged.

Question 96

Planck’s distribution law is valid for __________ bodies.

black
white
coloured
all (a), (b) & (c)

Answer 96

coloured

Question 97

For hot feed, forward feeding as compared to backward feeding results in __________ economy.

increased
decreased
no effect on
none of these

Answer 97

increased

Question 98

radiation energy is emitted by all the substances, which are above

0°K
0°C
100°C
room temperature

Answer 98

0°K

Question 99

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

εx + εy
εx⋅εy
1/εx + 1/εy
(εx + εy)/(εx + εy - εx⋅εy)

Answer 99

(εx + εy)/(εx + εy - εx⋅εy)

Question 100

What is the steam economy in case of a single effect evaporator system?

1
>1
< 1
0.1

Answer 100

< 1

Question 101

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
ha = 2hl
ha = 0.5 hl
ha = 0.75 hl

Answer 101

ha = 2hl

Question 102

jH factor for heat transfer is not a function of the __________ number.

Reynolds
Nusselt
Grashoff
both (b) & (c)

Answer 102

both (b) & (c)

Question 103

The Fourier number (defined as a.t/L2) is used in the analysis of problem involving heat transfer by

forced convection
natural convection
transient conduction
steady state conduction

Answer 103

transient conduction

Question 104

The energy radiated from a surface Q at absolute temperature T is related as

Q ∝ T^2
Q ∝ T^4
Q ∝ T^3
none of these

Answer 104

Q ∝ T^4

Question 105

Baffles are provided in heat exchangers to increase the

fouling factor
heat transfer area
heat transfer co-efficient
heat transfer rate

Answer 105

heat transfer co-efficient

Question 106

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)

0.5
0.05
0.1
0.15

Answer 106

0.1

Question 107

In case of a vertical tube evaporator, with increase in the liquor level, the

capacity of the evaporator is decreased.
capacity of the evaporator is increased.
true temperature drop increases.
both (b) and (c).

Answer 107

capacity of the evaporator is decreased.

Question 108

The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoffs law.

wavelength of radiation
nature of the body
temperature of the body
none of these

Answer 108

temperature of the body

Question 109

For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally

decreases
increases
remains unchanged
increases exponentially

Answer 109

decreases

Question 110

A 2-4 heat exchanger involves

only counter-flow of fluids.
only parallel-flow of fluids.
both counter and parallel-flow of the fluids.
smaller pressure drop compared to 1-2 exchanger.

Answer 110

both counter and parallel-flow of the fluids.

Question 111

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
> 1
1
∞

Answer 111

< 1

Question 112

With increase in temperature, the thermal conductivity of steel

increases
decreases
remains unchanged
increases exponentially

Answer 112

decreases

Question 113

Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids?

Dittus-Boeltier equation
Sieder-Tate equation
Nusselt equation
None of these

Answer 113

Sieder-Tate equation

Question 114

The main function of baffles provided in a shell and tube heat exchanger is to

facilitate the cleaning of outer tube surface.
enhance turbulence.
hold the tubes in position.
all ‘a’, ‘b’ & ‘c’.

Answer 114

enhance turbulence.

Question 115

In a single effect evaporator, the economy is

1
< 1
> 1
none of these

Answer 115

< 1

Question 116

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

0
1
>1
<1

Answer 116

<1

Question 117

Which of the following is not concerned with the heat transfer?

Brinkman number
Stanton number
Schmidt number
Peclet number

Answer 117

Schmidt number

Question 118

Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may be around __________ BTU.

180
970
3.97
none of these

Answer 118

180

Question 119

In counter flow compared to parallel flow,

LMTD is greater.
less surface area is required for a given heat transfer rate.
both (a) and (b).
more surface area is required for a given heat transfer rate.

Answer 119

both (a) and (b).

Question 120

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)

1000
727
800
1200

Answer 120

1000

Question 121

Crystallisation of solids from a homogeneous solution is a/an __________ process.

exothermic
mildly endothermic
highly endothermic
none of these

Answer 121

exothermic

Question 122

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

6000
24000
60000
48000

Answer 122

24000

Question 123

Value of Prandtl number for water ranges from

1 to 2
5 to 10
100 to 500
1000 to 2000

Answer 123

5 to 10

Question 124

Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by

eddies current
conduction
convection
none of these

Answer 124

conduction

Question 125

Among liquids, water has a comparatively high value of thermal conductivity, due to its

low density
high viscosity
partial ionisation
dense structure

Answer 125

partial ionisation

Question 126

Reynold’s analogy states that (where, St = Stanton number f = friction factor)

St = f/2
St=f/4
St = 4f
St = f^1/2

Answer 126

St = f/2

Question 127

For evaporation of viscous solution in a multiple effect evaporator, the preferred feeding scheme is

forward
backward
parallel
none of these

Answer 127

backward

Question 128

The sum of reflectivity and absorptivity for an opaque body is equal to

0.5
1
0
2

Answer 128

1

Question 129

The film thickness for laminar film condensation on vertical surface __________ from top to bottom.

cumulatively increases
cumulatively decreases
remains constant
and the surface conductance increase

Answer 129

cumulatively increases

Question 130

In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side __________ the heat transfer rate.

increases
decreases
does not affect
may increase or decrease, depends on the type of baffle

Answer 130

increases

Question 131

The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness)

∝ t
∝ 1/t
∝ sqrt(t)
independent of ‘t’

Answer 131

∝ 1/t

Question 132

Heat transfer co-efficient (h1) for liquids increases with

increasing temperature.
decreasing temperature.
decreasing Reynolds number.
none of these.

Answer 132

increasing temperature.

Question 133

A diathermaneous substance __________ the thermal radiation completely.

absorbs
reflects
transmits
none of these

Answer 133

transmits

Question 134

A hot body will radiate heat most rapidly, if its surface is

white & rough
black & rough
white & polished
black & polished

Answer 134

black & rough

Question 135

Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam.

0.4 - 0.6
1-1.3
1.8-2
2 - 2.4

Answer 135

1-1.3

Question 136

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

5.6
0.025
3.5
0.0035

Answer 136

0.025

Question 137

Analogy between mass and heat transfer is not applicable in case of

same velocity profile or equal eddy diffusivities.
thermal or pressure mass diffusion.
viscous heating or chemical reaction.
both (b) and (c).

Answer 137

both (b) and (c).

Question 138

A __________ surface has the maximum thermal emissivity out of the following.

black & smooth
black & rough
white & smooth
white & rough

Answer 138

black & rough

Question 139

Radiant energy received by a body is proportional to (where, d = the distance between the object emitting radiation and that receiving it.)

sqrt(d)
d
d^2
d^1.5

Answer 139

d^2

Question 140

Mechanical recompression evaporation is used in the production of

alcohol
distilled water
salt
fruits jam

Answer 140

distilled water

Question 141

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.

Condensation
Grashoff
Stantan
Brinkman

Answer 141

Brinkman

Question 142

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

0.35
0.45
0.55
0.85

Answer 142

0.45

Question 143

The purpose of providing a ‘catchall’ in the vapor line of an evaporator is to

create vacuum
regulate the vapor flow
vent the non-condensible gases
arrest the entrained liquid

Answer 143

arrest the entrained liquid

Question 144

What is the thermal conductivity of a perfect heat insulator?

zero
one
∞
between 0 and ∞

Answer 144

zero

Question 145

‘Fouling factor’ used in the design of a multipass shell and tube heat exchanger is a

non-dimensional factor.
factor of safety.
conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient.
none of these.

Answer 145

factor of safety.

Question 146

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
d^0.8
d^-0.2
d^-1
d^-1.8

Answer 146

d^-0.2

Question 147

Prandtl and Reynolds analogy are same, when Prandtl number is

0.5
1
> 2
1.5

Answer 147

1

Question 148

Heat transfer occurs by natural convection because change in temperature causes difference in

viscosity
density
thermal conductivity
heat capacity

Answer 148

density

Question 149

The ratio of kinematic viscosity to thermal diffusivity is called the __________ number.

Peclet
Prandtl
Stanton
Nusselt

Answer 149

Prandtl

Question 150

The critical radius ‘r’ of insulation on a pipe is given by

r = 2k/h
r = k/h
r = k/2h
r = h/k

Answer 150

r = k/h

Question 151

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the

temperature of the body only.
wavelength of monochromatic radiation.
both (a) and (b).
nature of material of body.

Answer 151

temperature of the body only.

Question 152

If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid

remains unchanged.
increases.
increases or decreases depending on number of shell passes.
decreases.

Answer 152

decreases.

Question 153

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

painting the surface black.
painting the surface white (with aluminium paint).
giving the surface a mirror finish.
roughening the surface.

Answer 153

painting the surface white (with aluminium paint).

Question 154

__________ paint has the maximum absorption coefficient.

Black
Yellow
White
Grey

Answer 154

Black

Question 155

What is Nusselt number ?

(Cp⋅μ)/k
hD/k
(h⋅Cp)/μ
(Cp⋅μ)/h

Answer 155

hD/k

Question 156

Steam traps are provided in steam carrying pipelines to

condense steam.
release excess steam pressure by bleeding steam.
remove condensate and inert gases.
none of these.

Answer 156

remove condensate and inert gases.

Question 157

The Dietus-Boelter equation for convective leat transfer cannot be used for

low Reynold’s number
very low Grashoff number
molten metals
all (a), (b) and (c)

Answer 157

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

Question 158

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

ellipse
straight line
parabola
circular arc

Answer 158

straight line

Question 159

Radiation heat transfer rates does not depend upon the

type of absorbing surface.
distance between the heat source and the object receiving the heat.
surface area and temperature of the heat source.
none of these.

Answer 159

none of these.

Question 160

Which of the following is correct ?

Rate = Driving force x Resistance
Driving force = Rate x Resistance
Resistance = Driving force x Rate
Rate = Resistance/Driving force

Answer 160

Driving force = Rate x Resistance

Question 161

Convective heat transfer, in which heat is transferred by movement of warmed matter is described by

Fourier’s law
Newton’s law of cooling
Fick’s law
none of these

Answer 161

Newton’s law of cooling

Question 162

As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient

continues to increase.
continues to decrease.
goes through a minimum.
goes through a maximum.

Answer 162

goes through a minimum.

Question 163

Heat transfer rate per unit area is called

thermal conductivity
heat flux
heat transfer co-efficient
thermal diffusivity

Answer 163

heat flux

Question 164

Log mean temperature difference (LMTD) cannot be used, if

heat transfer co-efficient over the entire heat exchanger is not constant.
there exists an unsteady state.
the heat capacity is not constant and there is a phase change.
none of these.

Answer 164

none of these.

Question 165

In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to __________ the velocity head.

twice
four times
square root of
square of

Answer 165

four times

Question 166

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

decrease
increase
first decrease and then increase
first increase and then decrease

Answer 166

first increase and then decrease

Question 167

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

minimum
maximum
zero
infinity

Answer 167

zero

Question 168

For what value of Prandtl number, the Col-burn analogy is valid?

0.06 to 120
0.6 to 120
1 to 103
l to 50

Answer 168

0.6 to 120

Question 169

In a forward feed multiple effect, the pressure build up will be

least at the inlet of the first effect.
least at the outlet of the last effect.
highest at the inlet of the last effect.
highest at the outlet of the last effect.

Answer 169

least at the outlet of the last effect.

Question 170

Film boiling is usually not desired in commercial equipments, because

the heat transfer rate is low in view of the large temperature drop.
it is difficult to maintain.
it is not economic.
none of these.

Answer 170

the heat transfer rate is low in view of the large temperature drop.

Question 171

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

3
0.33
1
1.33

Answer 171

1

Question 172

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

W/m.k
W/m
W/m.k^2
none, ‘a’ is just a number

Answer 172

W/m.k^2

Question 173

Film condensation is promoted on a/an __________ surface.

oily
coated
clean & smooth
dirty

Answer 173

clean & smooth

Question 174

Dietus-Boelter equation cannot be used for molten metals mainly due to its very low

Prandtl number
Grashoff number
thermal conductivity
viscosity

Answer 174

Prandtl number

Question 175

If Prandtl number is greater than the Schmidt number, then the

thermal boundary layer lies inside the concentration boundary layer.
concentration boundary layer lies inside the thermal boundary layer.
thermal & concentration boundary layers are of equal thickness.
hydrodynamic(i.e., momentum)boundary layer is thicker than the other two.

Answer 175

thermal boundary layer lies inside the concentration boundary layer.

Question 176

Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid?

Bleed point
Vent
Catchall
Baffle

Answer 176

Catchall

Question 177

Rate of heat transfer by vaporisation from pools of water is affected by the

nature of heating surface and distribution of bubbles.
surface tension of water.
viscosity of water.
all (a), (b) and (c).

Answer 177

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

Question 178

Multiple effect evaporators are commonly used in the manufacture of
P. Paper Q. Superphosphate
R. Sugar S. Fats

P and Q
P and R
P and S
R and S

Answer 178

P and S

Question 179

Which of the following has the highest thermal conductivity?

Brick
Air
Water
Silver

Answer 179

Silver

Question 180

Which of the following is unimportant in forced convection?

Reynolds number
Prandtl number
Grashhoff number
none of these

Answer 180

Grashhoff number

Question 181

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

vertical heat exchanger with steam on tube side.
vertical heat exchanger with steam on shell side.
horizontal heat exchanger with steam on tube side.
horizontal heat exchanger with steam on shell side.

Answer 181

vertical heat exchanger with steam on shell side.

Question 182

In a multiple effect evaporator, the effect of boiling point elevation is to

reduce the capacity
reduce the economy
increase the economy
none of these

Answer 182

reduce the capacity

Question 183

Dropwise condensation occurs on __________ surfaces.

clean and dirt free
smooth clean
contaminated cooling
polished

Answer 183

contaminated cooling

Question 184

For specified tube outside diameter, higher BWG means higher

tube thickness
cross-sectional area
weight per unit length
none of these

Answer 184

cross-sectional area

Question 185

Pick out the wrong statement.

Swenson-Walker crystalliser is a batch crystalliser.
Super saturation of the solution is the driving potential for a crystal growth.
The liquor left after the removal of crystals from a solution is called mother liquor.
The first stage of crystal formation is called nucleation.

Answer 185

Swenson-Walker crystalliser is a batch crystalliser.

Question 186

In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased.

velocity of circulation
liquor-film co-efficient
both (a) and (b)
neither (a) and (b)

Answer 186

neither (a) and (b)

Question 187

Electromagnetic radiations propagate in vacuum with a velocity of __________ metre/second.

3 x 10^5
3 x 10^8
3 x 10^10
3 x 10^12

Answer 187

3 x 10^8

Question 188

Heat flux is the time rate of heat transfer per unit

length
area
volume
none of these

Answer 188

area

Question 189

Film boiling occurs at __________ pressure.

atmospheric
sub-atmospheric
negative
very high

Answer 189

very high

Question 190

Heat flux through several resistances in series in analogous to the current flowing through several

resistances in parallel.
capacitors in series.
resistances in series.
none of these.

Answer 190

resistances in series.

Question 191

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

surrounding temperature.
average temperature of the fin.
temperature of the fin end.
constant temperature equal to that of the base

Answer 191

constant temperature equal to that of the base

Question 192

Vacuum is generally maintained in the vapour space of an evaporator mainly to

get economical temperature difference by using moderate pressure steam.
facilitate forward feeding in multiple effect evaporation.
concentrate heat sensitive materials.
achieve very high concentration of the final product.

Answer 192

get economical temperature difference by using moderate pressure steam.

Question 193

Double pipe heat exchangers are used

when heat transfer area required is very high.
when heat transfer area required is very low, i.e (100-200 ft^2).
because it occupies less floor area.
because it is less costly.

Answer 193

when heat transfer area required is very low, i.e (100-200 ft^2).

Question 194

Nusselt number (for forced convection heat transfer) is a function of the __________ number.

Prandtl
Reynolds
both (a) & (b)
neither (a) nor (b)

Answer 194

both (a) & (b)

Question 195

Pick out the wrong statement.

Heat transfer by radiation can not occur across an absolute volume.
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.
Propagation velocity for travel of heat radiation through vacuum is equal to the velocity of the light.
The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same.

Answer 195

Heat transfer by radiation can not occur across an absolute volume.

Question 196

Which type of heat exchanger is preferred for heavy heat loads?

Double pipe
Plate fine
Series and parallel set of shell and tube
None of these

Answer 196

Series and parallel set of shell and tube

Question 197

Pick out the wrong statement.

Reciprocal of the resistance to heat flow is called thermal conductance.
Unit of thermal conductance is W/°K.
Thermal conductance of a wall of thickness ‘L’, thermal conductivity ‘k’ and heat flow area ‘A’ is kL/A.
none of these.

Answer 197

Thermal conductance of a wall of thickness ‘L’, thermal conductivity ‘k’ and heat flow area ‘A’ is kL/A.

Question 198

While the total emissivity of a perfect black body is unity, the same for a real body is

0
1
> 1
between 0 and 1

Answer 198

between 0 and 1

Question 199

The Grashoff number is defined as the ratio of the

buoyancy to inertial forces.
buoyancy to viscous forces.
inertial to viscous forces.
buoyancy to surface tension forces.

Answer 199

buoyancy to viscous forces.

Question 200

According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor)

2f
f
f/2
f/4

Answer 200

f/2

Question 201

The absorptivity of a body is equal to its emissivity

at a particular temperature.
for circular bodies.
under thermal equilibrium.
none of these.

Answer 201

under thermal equilibrium.

Question 202

Absorptivity and refletivity of a perfect black body are respectively,

1 and 0
0 and 1
1 and ∞
0 and 0.5

Answer 202

1 and 0

Question 203

In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)

α = 1; ε ≠ 1
α ≠ 1, ε = 1
α ≠ 1, ε ≠ 1
α = 1; ε = 1

Answer 203

α = 1; ε = 1

Question 204

Pick out the wrong statement.

Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient.
In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles.
S.I. unit of fouling factor is Watt/m2.°K.
Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube.

Answer 204

S.I. unit of fouling factor is Watt/m2.°K.

Question 205

When warm and cold liquids are mixed, the heat transfer is mainly by

conduction
convection
radiation
both(a) & (c)

Answer 205

convection

Question 206

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?

Cube
Plate
Sphere
All will cool at the same rate

Answer 206

Sphere

Question 207

Vent pipes are provided in a condenser to

remove non-condensable gases.
purge the condenser.
facilitate easy cleaning of tubes.
none of these.

Answer 207

remove non-condensable gases.

Question 208

Heat transfer by natural convection is enhanced in system with

high viscosity.
high co-efficient of thermal expansion.
low temperature gradients.
low density change with temperature.

Answer 208

high co-efficient of thermal expansion.

Question 209

In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid.

nucleate
pool
low pressure
none of these

Answer 209

pool

Question 210

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.

10
>10
<10
either (b) or (c), depends on the mass of the body

Answer 210

> 10

Question 211

In forced convection, the Nusselt number is a function of

Re and Pr
Re and Gr
Pr and Gr
Re and Sc

Answer 211

Re and Pr

Question 212

At what value of Prandtl number, the hydrodynamic and thermal boundary layers are identical?

0.5
1
1.5
80

Answer 212

1

Question 213

A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because

total heat transfer area of all the effects is -less than that in a single effect evaporator system.
total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect.
boiling point elevation in a single effect system is much higher than that in any effect in a multieffect system.
heat transfer co-efficient in a single effect is much lower than that in any effect in a multieffect system.

Answer 213

total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect.

Question 214

Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by

keeping the heat transfer surface clean.
enhancing the fluid pumping rate.
increasing the tube length.
none of these.

Answer 214

keeping the heat transfer surface clean.

Question 215

Trap is used to remove __________ from steam pipe lines.

steam
condensate
non-condensables
none of these

Answer 215

condensate

Question 216

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

125
133
150
160

Answer 216

160

Question 217

Tube pitch is the __________ of tube diameters and the clearances.

sum
difference
ratio
none of these

Answer 217

sum

Question 218

With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer

decreases
increases
increases exponentially
remains unaffected

Answer 218

decreases

Question 219

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.

more
less
same
unpredictable

Answer 219

less

Question 220

Natural convection is characterised by

Grashhoff number
Peclet number
Reynolds number
Prandtl number

Answer 220

Grashhoff number

Question 221

Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is

0.72
4.364
18
83

Answer 221

4.364

Question 222

Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is

1
< 1
> 1
> 5

Answer 222

< 1

Question 223

The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe )

K/h0
2K/h0
hi/K
2hi/K

Answer 223

K/h0

Question 224

The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature)
(ΔT)^2
(ΔT)^4
(ΔT)^3
sqrt(ΔT)

Answer 224

(ΔT)^3

Question 225

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

∞
0
equal to the difference between hot and cold fluids inlet temperature.
equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature.

Answer 225

0

Question 226

A body is called grey if the monochromatic emissivity of the body is

zero
unity
same for all wavelengths
different for all wavelengths

Answer 226

same for all wavelengths

Question 227

In an extended surface heat exchanger, fluid having lower co-efficient

flows through the tube.
flows outside the tubes.
can flow either inside or outside the tubes.
should not be used as it gives very high pressure drop.

Answer 227

flows outside the tubes.

Question 228

In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is

infinity.
zero.
same as average heat transfer co-efficient for tube side.
none of these.

Answer 228

infinity.

Question 229

Grashoff number, which is defined as g . β(Ts - T∞) ρ2. L3/μ2, is proportional to the ratio of buoyancy force to __________ force.

viscous
elastic
inertial
none of these

Answer 229

viscous

Question 230

Pick out the wrong statement.

By increasing the number of shell passes, the temperature cross in a shell and tube heat exchanger can be prevented.
An underdesigned steam trap will back up the condensate instead of discharging it out.
Steam condensate is corrosive because of the presence of dissolved oxygen in it.
Film boiling is desirable in commercial equipments due to high heat transfer rate at low temperature drop.

Answer 230

Film boiling is desirable in commercial equipments due to high heat transfer rate at low temperature drop.

Question 231

Graetz number is given by

mCp/kL
kL/mCp
mCp/kμ
kL/mCp

Answer 231

mCp/kL

Question 232

For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in

increased economy
decreased economy
lower capacity
no effect on economy

Answer 232

increased economy

Question 233

Economy of an evaporator is influenced by the

steam pressure
feed temperature
number of effect
both(b) & (c)

Answer 233

both(b) & (c)

Question 234

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.

hyperbolic
parabolic
linear
logarithmic

Answer 234

linear

Question 235

In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred

through a metallic wall.
by direct contact of hot flue gas with air.
by heating an intermediate material (like chequor bricks) and then heating the air from this hot material.
none of these.

Answer 235

by heating an intermediate material (like chequor bricks) and then heating the air from this hot material.

Question 236

__________ equation relates the thermal conductivity of a solid to its temperature.

Antonie
Kopp’s
Lee’s
Kistyakowski

Answer 236

Lee’s

Question 237

For small temperature difference, the heat transfer rate as per Newton’s law of cooling is proportional to (where, Δt = excess temperature)

Δt
Δt^2
Δt^3
sqrt(Δt)

Answer 237

Δt

Question 238

Pick out the wrong statement.

The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation.
Film co-efficient for vaporisation decreases as a result of vapor binding.
In industrial practice, sub-cooling of condensate is required, when the condensate is a volatile liquid and is to be transferred for storage.
Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher.

Answer 238

Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film co-efficient, which is higher.

Question 239

Viscous & heat sensitive liquids are concentrated in __________ evaporators.

open pan
long tube
agitated film
none of these

Answer 239

agitated film

Question 240

1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C.

1.49
1
4.88
none of these

Answer 240

1.49

Question 241

Heat transfer by radiation between two bodies at T1 & T2 and in an ambient temperature of Ta°C depends on

T1 - T2
T1 - Ta
T2 - Ta
none of these

Answer 241

none of these

Question 242

The ratio of momentum diffusivity to thermal diffusivity is the __________ number.

Prandtl
Nusselt
Stanton
Grashoff

Answer 242

Prandtl

Question 243

For a perfectly transparent surface (like gases), the

absorptivity = 0
transmissivity = 1
reflectivity = 0
all (a), (b) & (c)

Answer 243

transmissivity = 1

Question 244

For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and pressure drop are

same
different
never different
linearly related

Answer 244

different

Question 245

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

Answer 245

supersaturated

Question 246

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

4000
9000
4600
3000

Answer 246

4000

Question 247

An insulator should have

low thermal conductivity.
high thermal conductivity.
less resistance to heat flow.
a porous structure.

Answer 247

low thermal conductivity.

Question 248

In a backward feed multiple effect evaporator

feed is introduced in the first effect.
feed flows from low pressure to high pressure.
no pumps are required between successive effects.
none of these.

Answer 248

feed flows from low pressure to high pressure.

Question 249

Choose the correct equation.

Nu = (Re) (Pr) (Gz)
Nu = (Re) (Pr) (St)
Nu = (Re)(Pr)
Nu = (Pr)(St)

Answer 249

Nu = (Re) (Pr) (St)

Question 250

In a forward feed multiple effect evaporator unit

viscosity of liquid is highest in first effect.
transfer from effect to effect is done by pumps.
no pump is required to withdraw the product from the last effect.
none of these.

Answer 250

none of these.

Question 251

In case of heat flow by conduction for a cylindrical body with an internal heat source, the nature of temperature distribution is

linear
hyperbolic
parabolic
none of these

Answer 251

parabolic

Question 252

For heat flow through very thick-walled cylinder, use____mean radius.

arithmetic
logarithmic
geometric
either (a) or (c)

Answer 252

logarithmic

Question 253

Indirect contact heat exchangers are preferred over direct contact heat exchangers, because

heat transfer co-efficient are high.
there is no risk of contamination.
there is no mist formation.
cost of equipment is lower.

Answer 253

there is no risk of contamination.

Question 254

Water is normally used as a coolant in the heat exchange equipments mainly because ofits

abundance & high heat capacity
low density
low viscosity
high fluidity

Answer 254

abundance & high heat capacity

Question 255

The rate of emission of radiation by a body does not depend upon the

wavelength of radiation.
surface temperature of the body.
nature of the surface.
shape and porosity of the body.

Answer 255

shape and porosity of the body.

Question 256

Which of the following has maximum thermal conductivity at the same temperature?

Steel
Petrol
Air
All have the same conductivity

Answer 256

Steel

Question 257

Maximum heat transfer rate is obtained in __________ flow.

laminar
turbulent
creeping
transition region

Answer 257

turbulent

Question 258

In case of __________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface.

nucleate
local
pool
saturated

Answer 258

local

Question 259

The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is

2
1/2
4
1/4

Answer 259

1/4

Question 260

Terminal point temperature differences between fluids in case of a heat exchanger is termed as

approach.
log mean temperature difference.
arithmetic mean temperature difference.
geometric mean temperature difference.

Answer 260

approach.

Question 261

LMTD can’t be used as such without a correction factor for the

multipass heat exchanger.
baffled heat exchanger.
condensation of mixed vapour in a condenser.
all (a) (b) and (c).

Answer 261

all (a) (b) and (c).

Question 262

Fqra cold viscous feed, backward feed gives __________ than forward feed.

a higher capacity
a lower capacity
lower economy
none of these

Answer 262

a higher capacity

Question 263

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?

35.5
43.75
81.25
48.25

Answer 263

81.25

Question 264

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

U1 = U2
U2 > U1
U1 > U2
U1 = dirt factor - U2

Answer 264

U1 = U2

Question 265

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

Answer 265

Watt/m.°K

Question 266

Boiling point of a solution according to Duhring’s rule is a linear function of the __________ of water.

boiling point (at the same pressure)
viscosity
density
thermal conductivity

Answer 266

boiling point (at the same pressure)

Question 267

The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.

average
geometric mean
product
sum

Answer 267

sum

Question 268

At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe?

0.5
< 0.5
> 0.6
< 0.1

Answer 268

> 0.6

Question 269

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

0
R2/(R1+R2)
1
(R1/R2)^2

Answer 269

R2/(R1+R2)

Question 270

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

1.26 h1
0.794 h1
0.574 h1
1.741 h1

Answer 270

0.794 h1

Question 271

The main purpose of providing fins on heat transfer surface is to increase the

temperature gradient.
mechanical strength of the equipment.
heat transfer area.
heat transfer co-efficient.

Answer 271

heat transfer area.

Question 272

A BTU/hr.ft.2 °F is equal to

1 kcal/hr. m2°C.
4.88 kcal/hr. m.2°C.
1 kcal/hr. m2.°K.
none of these.

Answer 272

4.88 kcal/hr. m.2°C.

Question 273

Which of the following has the lowest Prandtl number?

Molten sodium (a coolant used in fast breeder reactor)
Water
Transformer oil
Dilute H2SO4

Answer 273

Molten sodium (a coolant used in fast breeder reactor)

Question 274

In SI units, fouling factor is expressed in

m2°K/W
W/m2°K
m2°K
m°K/W

Answer 274

m2°K/W

Question 275

An ejector is used to

increase pressure
increase temperature
remove condensate
none of these

Answer 275

none of these

Question 276

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

less corrosion problems.
flexibility possible in the baffle arrangement.
low pressure drop.
high heat transfer co-efficient.

Answer 276

flexibility possible in the baffle arrangement.

Question 277

All analogy equations connecting friction factor and heat transfer co-efficient apply only to

wall or skin friction
form friction
both (a) and (b)
turbulent flow

Answer 277

wall or skin friction

Question 278

Electro-magnetic spectrum range, which is important for radiation varies from __________ microns.

1 to 100
0.5 to 50
10 to 100
100 to 1000

Answer 278

0.5 to 50

Question 279

The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are

Re, Gz
Nu, Pr
Nu, Pr, Re
Nu, Gz

Answer 279

Nu, Gz

Question 280

Heat transfer rate described by Fourier’s law will decrease, if the __________ increases.

thermal conductivity
thickness
temperature difference
heat transfer area

Answer 280

thickness

Question 281

A black body does not __________ radiation.

absorb or emit
refract
reflect
both(b) & (c)

Answer 281

both(b) & (c)

Question 282

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

solution has an elevation of boiling point.
evaporators operate under vacuum.
evaporators opreate at atmospheric pressure.
none of these.

Answer 282

solution has an elevation of boiling point.

Question 283

Peclet number (Pe) is given by

Pe = Re.Pr
Pe = Re/Pr
Pe = Pr/Re
Pe = Nu.Re

Answer 283

Pe = Re.Pr

Question 284

Nusselt number is the ratio of the

temperature gradient of the wall to that across the entire pipe.
temperature difference to the temperature gradient at the wall.
heat flux at the wall to that across the entire pipe.
none of these

Answer 284

heat flux at the wall to that across the entire pipe.

Question 285

Prandtl number is the ratio of

momentum diffusivity to mass diffusivity.
momentum diffusivity to thermal diffusivity.
thermal diffusivity to mass diffusivity.
thermal diffusivity to momentum diffusivity.

Answer 285

momentum diffusivity to thermal diffusivity.

Question 286

Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger?

Tube side pressure drop and the heat transfer rate.
Convective heat transfer co-efficient.
Effective tube surface area for convective heat transfer.
All (a) (b) and (c).

Answer 286

All (a) (b) and (c).

Question 287

Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator?

Long vertical evaporator
Horizontal tube evaporator
Agitated film evaporator
Calenderia vertical tube evaporator

Answer 287

Agitated film evaporator

Question 288

“The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium”. This is __________ law.

Kirchoffs
Planck’s
Wien’s displacement
Stefan-Boltzman

Answer 288

Kirchoffs

Question 289

View factor is important in heat transfer by

steady state conduction
natural convection
forced convection
radiation

Answer 289

radiation

Question 290

The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is

lower tube side pressure drop.
lower shell side pressure drop.
higher tube side heat transfer co-efficient.
higher shell side heat transfer co-efficient.

Answer 290

higher tube side heat transfer co-efficient.

Question 291

For a multipass shell and tube heat exchanger, the LMTD correction factor is always

1
> 1
< 1
between 1 & 2

Answer 291

< 1

Question 292

If heat transfer rate varies with the time, it is termed as

forced convection
steady state conduction
monochromatic radiation
none of these

Answer 292

none of these

Question 293

Pick out the wrong statement.

Fluid movement under the influence of buoyant forces resulting from change in density takes place in case of natural convection.
The ratio NNu/NRe . Npr is called the Stanton number.
The Peclet number is a measure of the ratio of energy transport by convection to that by conduction.
The Colbum jH factor for heat transfer is given by Nst Npr.

Answer 293

The Colbum jH factor for heat transfer is given by Nst Npr.

Question 294

Tube expansion allowances exist in __________ heat exchanger.

multipass fixed tube sheet
U-tube
single pass fixed tube sheet
none of these

Answer 294

U-tube

Question 295

Pick out the wrong statement.

In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2.
Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number.
Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger.
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.

Answer 295

Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger.

Question 296

Agitated film evaporator is suitable for concentrating __________ liquids.

foaming
viscous
very thin
corrosive

Answer 296

viscous

Question 297

The thickness of condensate layer in filmwise condensation depends on the

condensation rate
surface configuration
liquid flow rate from the surface
all (a), (b) and (c)

Answer 297

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

Question 298

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.

parabolic
hyperbolic
linear
logarithmic

Answer 298

parabolic