Heat Transfer

Question 1

Crystal size in a continuous crystalliser depends upon the

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

Answer 1

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

Question 2

Heat waves

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

Answer 2

d) both (b) and (c).

Question 3

Air is best heated with steam in a heat exchanger of

a) plate type.
b) double pipe type with fin on steam side.
c) double pipe type with fin on air side.
d) shell and tube type.

Answer 3

c) double pipe type with fin on air side.

Question 4

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

a) Gases
b) Solids
c) Liquids
d) Both (b) and (c)

Answer 4

d) Both (b) and (c)

Question 5

Black liquor generated during paper manufacture is concentrated in a

a) single effect evaporator.
b) single effect evaporator followed by a crystalliser.
c) multiple effect evaporator.
d) multiple effect evaporators followed by a crystalliser.

Answer 5

c) multiple effect evaporator.

Question 6

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

a) film boiling
b) nucleate boiling
c) vapour binding
d) none of these

Answer 6

b) 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)

a) C/E
b) E/C
c) CE
d) 1/CE

Answer 7

a) C/E

Question 8

Reynold’s analogy states that

a) Nst α f
b) Nst α NRe
c) NNu α f
d) NRe α f

Answer 8

a) Nst α f

Question 9

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

a) decreases
b) increases
c) remains constant
d) first decreases upto certain temperature and then increases

Answer 9

b) increases

Question 10

Fourier’s law applies to the heat transfer by

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

Answer 10

c) conduction

Question 11

Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
baffle spacing & shell diameter.

a) tube diameter & pitch.
b) viscosity, density & mass
c) velocity of shell side fluid.
d) none of these.

Answer 11

d) none of these.

Question 12

In the equation Q = UAΔt; Δt is

a) geometric mean temperature difference.
b) arithmetic mean temperature difference.
c) logarithmic mean temperature difference.
d) the difference of average bulk temperatures of hot and cold fluids.

Answer 12

c) logarithmic mean temperature difference.

Question 13

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

a) increases
b) decreases
c) remains unchanged
d) may increase or decrease; depends on the solid

Answer 13

b) decreases

Question 14

For an ideal black body

a) absorptivity = 1
b) reflectivity = 1
c) emissivity = 0
d) transmissivity = 1

Answer 14

a) absorptivity = 1

Question 15

Fouling factor

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

Answer 15

c) accounts for additional resistances to heat flow.

Question 16

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

a) increases
b) decreases
c) is not affected
d) may increase or decrease; depends on the feed

Answer 16

b) decreases

Question 17

The steam ejector is used to

a) remove condensate from the steam pipelines.
b) create vacuum.
c) superheat the steam.
d) none of these.

Answer 17

b) create vacuum.

Question 18

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

a) increases
b) decreases
c) remains constant
d) passes through a maxima

Answer 18

d) passes through a maxima

Question 19

In a heat exchanger, floating head is provided to

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

Answer 19

c) relieve stresses caused by thermal expansion.

Question 20

Leidenfrost point is a term concerned with the

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

Answer 20

d) boiling of a liquid on a hot surface.

Question 21

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

a) counter flow with process stream on shell side.
b) counter flow with process stream on tube side.
c) parallel flow with process stream on shell side.
d) parallel flow with process stream on tube side.

Answer 21

a) counter flow with process stream on shell side.

Question 22

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

a) IR
b) (I^2)R
c) IR^2
d) (I^2)(R^2)

Answer 22

b) (I^2)R

Question 23

Pick out the wrong statement.

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

Answer 23

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

Question 24

Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.

a) laminar
b) transition
c) both ‘a’ & ‘b’
d) highly turbulent

Answer 24

d) highly turbulent

Question 25

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

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

Answer 25

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

Question 26

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

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

Answer 26

b) mercury

Question 27

Presence of a non-condensing gas in a condensing vapour

a) increases the rate of condensation.
b) decreases thermal resistance.
c) is desirable to increase the film co-efficient.
d) none of these.

Answer 27

d) none of these.

Question 28

Kirchoff s law applies to __________ radiation.

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

Answer 28

c) both (a) & (b)

Question 29

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

a) increases.
b) decreases.
c) remains unchanged.
d) may increase or decrease ; depending on temperature.

Answer 29

a) increases.

Question 30

In case of evaporators, liquid entrainment results primarily due to

a) high vacuum in the evaporator.
b) high evaporation rate.
c) foaming of the solution.
d) high heat transfer rate.

Answer 30

c) foaming of the solution.

Question 31

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

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

Answer 31

c) increase the shell side heat transfer co-efficient.

Question 32

Air is to be heated by condensing steam. Two heat exchangers are available (i) a shell and tube heat exchanger and (ii) a finned tube heat exchanger. Tube side heat transfer area are equal in both the cases. The recommended arrangement is

a) finned tube heat exchanger with air inside and steam outside.
b) finned tube heat exchanger with air outside and steam inside.
c) shell and tube heat exchanger with air inside tubes and steam on shell side.
d) shell and tube heat exchanger with air on shell side and steam inside tubes.

Answer 32

b) finned tube heat exchanger with air outside and steam inside.

Question 33

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

a) J/M^2°K
b) W/m^2°K
c) W/m°K
d) J/m°K

Answer 33

b) W/m^2°K

Question 34

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

a) capacity
b) rate of evaporation
c) economy
d) rate of vaporisation

Answer 34

c) economy

Question 35

Pick out the wrong statement.

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

Answer 35

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

Question 36

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

a) boiling point elevations
b) temperature of the feed
c) rate of heat transfer
d) ratio of the weight of the thin liquor to thick liquor

Answer 36

a) boiling point elevations

Question 37

Increasing the liquor level in the evaporator results in the

a) decreased capacity.
b) increase in liquor film co-efficient.
c) decreased effect of hydrostatic head.
d) increased true temperature drop.

Answer 37

a) decreased capacity.

Question 38

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

a) smaller than
b) greater than
c) equal to
d) not related with

Answer 38

a) smaller than

Question 39

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

a) no
b) the least
c) the largest
d) lower

Answer 39

c) the largest

Question 40

Thermal conductivity of a conducting solid material depends upon its

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

Answer 40

c) both (a) & (b)

Question 41

Pick out the wrong statement.

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

Answer 41

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

Question 42

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

a) (ΔT)^2
b) √ΔT
c) (ΔT)^(1/4)
d) (ΔT)^(3/2)

Answer 42

c) (ΔT)^(1/4)

Question 43

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

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

Answer 43

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

Question 44

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

a) Lewis relationship
b) Nusselt number
c) Kutateladze number
d) Froude number

Answer 44

a) Lewis relationship

Question 45

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

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

Answer 45

a) higher economy

Question 46

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

a) Logarithmic mean area
b) Arithmetic mean area
c) Geometric mean area
d) None of these

Answer 46

a) Logarithmic mean area

Question 47

Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place

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

Answer 47

b) between two bodies not in physical contact with each other.

Question 48

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

a) Nusselt number.
b) Sherwood number.
c) Schmidt number.
d) Stanton number.

Answer 48

c) Schmidt number.

Question 49

Finned tube heat exchangers

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

Answer 49

a) give larger area per tube.

Question 50

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

a) increases
b) decreases
c) remains constant
d) may increase or decrease ; depends on the material

Answer 50

d) may increase or decrease ; depends on the material

Question 51

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

a) Planck’s law
b) Kirchhoffs law
c) Wien’s law
d) Stefan-Boltzman law

Answer 51

a) Planck’s law

Question 52

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

a) 1.5
b) 1
c) > 1
d) < 1

Answer 52

b) 1

Question 53

In a shell and tube heat exchanger,

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

Answer 53

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

Question 54

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

a) for fluids in laminar flow.
b) for fluids in tubulent flow.
c) when Grashhoff number is very important.
d) for liquid metals.

Answer 54

b) for fluids in tubulent flow.

Question 55

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

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

Answer 55

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

Question 56

Out of the following four assumptions used in the derivation of the equation for LMTD, which one is subject to the largest deviation in practice?

a) Constant overall heat transfer co-efficient.
b) Constant rate of fluid flow.
c) Constant specific heat.
d) No partial phase change in the system.

Answer 56

b) Constant rate of fluid flow.

Question 57

Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because

a) convection becomes important
b) conduction becomes important
c) radiation becomes important
d) sub-cooled boiling occurs

Answer 57

c) radiation becomes important

Question 58

Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow. )

a) t
b) 1/ρ
c) 1/A
d) all (a), (b) & (c)

Answer 58

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

Question 59

Temperature profile in steady state heat transfer is

a) asymptotic
b) hyperbolic
c) parabolic
d) linear

Answer 59

d) linear

Question 60

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

a) decreases the pressure drop.
b) decreases the outlet temperature of cooling medium.
c) increases the overall heat transfer coefficient.
d) none of these.

Answer 60

c) increases the overall heat transfer coefficient.

Question 61

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

a) pool
b) nucleate
c) transition
d) film

Answer 61

d) film

Question 62

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

a) 0.2 D
b) 0.5 D
c) 0.66 D
d) 0.80 D

Answer 62

a) 0.2 D

Question 63

Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )

a) t^4
b) T^4
c) 1/(t^4)
d) 1/(T^4)

Answer 63

b) T^4

Question 64

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

a) 2.36
b) 4.36
c) 120.36
d) dependent on NRe only

Answer 64

b) 4.36

Question 65

What is the unit of thermal conductivity ?

a) Kcal/hrm^2°C
b) Kcal/hrm°C
c) Kcal/hrm
d) Kcal/hr°C

Answer 65

b) Kcal/hrm°C

Question 66

The thermal radiation emitted by a body is proportional to Tn, where T is its absolute temperature. The value of ‘n’ is exactly 4 for

a) black painted bodies only
b) all bodies
c) polished bodies only
d) a black body

Answer 66

b) all bodies

Question 67

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

a) high temperature
b) high pressure
c) low film co-efficient
d) none of these

Answer 67

c) low film co-efficient

Question 68

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

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

Answer 68

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

Question 69

For flow over a flat plate, the ratio of thermal boundary layer thickness, ‘xt’ and hydrodynamic boundary layer thickness ‘x’ is equal to (where, NPr = Prandtl number)

a) NPr
b) NPr^(1/3)
c) NPr^(-1)
d) NPr^(-1/3)

Answer 69

b) NPr^(1/3)

Question 70

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

a) 0.38-0.78
b) 0.5-50
c) 100-1000
d) 5-50

Answer 70

b) 0.5-50

Question 71

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

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

Answer 71

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

Question 72

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

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

Answer 72

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

Question 73

Economy of a multiple effect evaporator depends upon the

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

Answer 73

a) heat balance consideration

Question 74

The Graetz number is concerned with the

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

Answer 74

d) heat transfer in laminar flow.

Question 75

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

a) called the view factor.
b) called the angle of vision.
c) proportional to the square of the distance between surfaces.
d) expressed in terms of radians.

Answer 75

b) called the angle of vision.

Question 76

Pick out the wrong statement.

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

Answer 76

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

Question 77

In forced convection, the heat transfer depends on

a) Re, Pr
b) Re, Gr
c) mainly Gr
d) Re only

Answer 77

a) Re, Pr

Question 78

With increase in temperature, the thermal conductivity of most liquids

a) increases
b) decreases
c) remains same
d) first increases upto a certain temperature and then becomes constant

Answer 78

b) decreases

Question 79

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

a) conduction
b) natural convection
c) forced convection
d) radiation

Answer 79

d) radiation

Question 80

Pick out the correct statement.

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

Answer 80

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

Question 81

In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used

a) in low range of temperature differences.
b) in high range of temperature differences.
c) because of its low cost.
d) to prevent corrosion of the tube bundles.

Answer 81

b) in high range of temperature differences.

Question 82

Stefan-Boltzman law applies to __________ body.

a) black
b) white
c) grey
d) any colour

Answer 82

a) black

Question 83

The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is

a) more
b) less
c) some
d) either more or less ; depends on the nature of vapor

Answer 83

c) some

Question 84

A perfect black body is a perfect __________ of radiation.

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

Answer 84

c) both (a) & (b)

Question 85

In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid.

a) equal to
b) more than
c) less than
d) either more or less than (depending upon the fluid)

Answer 85

a) equal to

Question 86

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

a) boiler
b) heat exchanger
c) recuperator
d) regenerator

Answer 86

b) heat exchanger

Question 87

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

a) Strouhal number
b) Sherwood number
c) Euler number
d) Grashoff number

Answer 87

d) Grashoff number

Question 88

Pick out the wrong statement:

a) With change in temperature, the radiant energy emitted by a black body remains unchanged.
b) Absorptivity of a body approaches unity in case of diffuse reflection.
c) Absorptivity of a perfectly black body is unity.
d) Value of Stefan-Boltzman constant is 4.876 x 10^(-8) KCal/m^2hr°K^4.

Answer 88

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

Question 89

Planck’s distribution law is valid for __________ bodies.

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

Answer 89

c) coloured

Question 90

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

a) increased
b) decreased
c) no effect on
d) none of these

Answer 90

a) increased

Question 91

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

a) 0°K
b) 0°C
c) 100°C
d) room temperature

Answer 91

a) 0°K

Question 92

The interchange factor for radiation heat transfer from surface ‘x’ to surface ‘y’ in case of an infinite parallel planes with emis-sivities εx & εy is given by

a) εx + εy
b) εx * εy
c) (1/εx) + (1/εy)
d) (εx + εy) / (εx + εy - εx * εy)

Answer 92

d) (εx + εy) / (εx + εy - εx * εy)

Question 93

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

a) 1
b) >1
c) < 1
d) 0.1

Answer 93

c) < 1

Question 94

If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length

a) ha = hl
b) ha = 2hl
c) ha = 0.5 hl
d) ha = 0.75 hl

Answer 94

b) ha = 2hl

Question 95

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

a) Reynolds
b) Nusselt
c) Grashoff
d) both (b) & (c)

Answer 95

d) both (b) & (c)

Question 96

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

a) forced convection
b) natural convection
c) transient conduction
d) steady state conduction

Answer 96

c) transient conduction

Question 97

Baffles are provided in heat exchangers to increase the

a) fouling factor
b) heat transfer area
c) heat transfer co-efficient
d) heat transfer rate

Answer 97

c) heat transfer co-efficient

Question 98

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

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

Answer 98

a) capacity of the evaporator is decreased.

Question 99

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

a) wavelength of radiation
b) nature of the body
c) temperature of the body
d) none of these

Answer 99

c) temperature of the body

Question 100

A 2-4 heat exchanger involves

a) only counter-flow of fluids.
b) only parallel-flow of fluids.
c) both counter and parallel-flow of the fluids.
d) smaller pressure drop compared to 1-2 exchanger.

Answer 100

c) both counter and parallel-flow of the fluids.

Question 101

In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always

a) < 1
b) > 1
c) 1
d) ∞

Answer 101

a) < 1

Question 102

With increase in temperature, the thermal conductivity of steel

a) increases
b) decreases
c) remains unchanged
d) increases exponentially

Answer 102

b) decreases

Question 103

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

a) Dittus-Boeltier equation
b) Sieder-Tate equation
c) Nusselt equation
d) None of these

Answer 103

b) Sieder-Tate equation

Question 104

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

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

Answer 104

b) enhance turbulence.

Question 105

In a single effect evaporator, the economy is

a) 1
b) < 1
c) > 1
d) none of these

Answer 105

b) < 1

Question 106

LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is

a) 0
b) 1
c) >1
d) <1

Answer 106

d) <1

Question 107

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

a) Brinkman number
b) Stanton number
c) Schmidt number
d) Peclet number

Answer 107

c) Schmidt number

Question 108

In counter flow compared to parallel flow,

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

Answer 108

c) both (a) and (b).

Question 109

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

a) exothermic
b) mildly endothermic
c) highly endothermic
d) none of these

Answer 109

a) exothermic

Question 110

Value of Prandtl number for water ranges from

a) 1 to 2
b) 5 to 10
c) 100 to 500
d) 1000 to 2000

Answer 110

b) 5 to 10

Question 112

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

a) eddies current
b) conduction
c) convection
d) none of these

Answer 112

b) conduction

Question 113

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

a) low density
b) high viscosity
c) partial ionisation
d) dense structure

Answer 113

c) partial ionisation

Question 114

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

a) St = f/2
b) St = f/4
c) St = 4f
d) St = f1/2

Answer 114

a) St = f/2

Question 115

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

a) forward
b) backward
c) parallel
d) none of these

Answer 115

b) backward

Question 116

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

a) 0.5
b) 1
c) 0
d) 2

Answer 116

b) 1

Question 117

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

a) cummulatively increases
b) cummulatively decreases
c) remains constant
d) and the surface conductance increase

Answer 117

a) cummulatively increases

Question 118

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

a) increases
b) decreases
c) does not affect
d) may increase or decrease, depends on the type of baffle

Answer 118

a) increases

Question 119

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

a) ∝ t
b) ∝ 1/t
c) ∝ √t
d) independent of ‘t’

Answer 119

b) ∝ 1/t

Question 120

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

a) increasing temperature.
b) decreasing temperature.
c) decreasing Reynolds number.
d) none of these.

Answer 120

a) increasing temperature.

Question 121

A diathermaneous substance __________ the thermal radiation completely.

a) absorbs
b) reflects
c) transmits
d) none of these

Answer 121

c) transmits

Question 122

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

a) white & rough
b) black & rough
c) white & polished
d) black & polished

Answer 122

b) black & rough

Question 123

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

a) 0.4 - 0.6
b) 1-1.3
c) 1.8-2
d) 2 - 2.4

Answer 123

b) 1-1.3

Question 124

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

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

Answer 124

d) both (b) and (c).

Question 125

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

a) black & smooth
b) black & rough
c) white & smooth
d) white & rough

Answer 125

b) black & rough

Question 126

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

a) √d
b) d
c) d^2
d) d^1.5

Answer 126

c) d^2

Question 127

Mechanical recompression evaporation is used in the production of

a) alcohol
b) distilled water
c) salt
d) fruits jam

Answer 127

b) distilled water

Question 128

A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the __________ number.

a) Condensation
b) Grashoff
c) Stantan
d) Brinkman

Answer 128

d) Brinkman

Question 129

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

a) create vacuum
b) regulate the vapor flow
c) vent the non-condensible gases
d) arrest the entrained liquid

Answer 129

d) arrest the entrained liquid

Question 130

What is the thermal conductivity of a perfect heat insulator ?

a) zero
b) one
c) ∞
d) between 0 and ∞

Answer 130

a) zero

Question 131

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

a) non-dimensional factor.
b) factor of safety.
c) conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient.
d) none of these.

Answer 131

b) factor of safety.

Question 132

A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter ‘d’. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to

a) d^0.8
b) d^-0.2
c) d^-1
d) d^-1.8

Answer 132

b) d^-0.2

Question 133

Prandtl and Reynolds analogy are same, when Prandtl number is

a) 0.5
b) 1
c) > 2
d) 1.5

Answer 133

b) 1

Question 134

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

a) viscosity
b) density
c) thermal conductivity
d) heat capacity

Answer 134

b) density

Question 135

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

a) r = 2k/h
b) r = k/h
c) r = k/2h
d) r = h/k

Answer 135

b) r = k/h

Question 136

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

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

Answer 136

a) temperature of the body only.

Question 137

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

a) remains unchanged.
b) increases.
c) increases or decreases depending on number of shell passes.
d) decreases.

Answer 137

d) decreases.

Question 138

The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by

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

Answer 138

b) painting the surface white (with aluminium paint).

Question 139

__________ paint has the maximum absorption coefficient.

a) Black
b) Yellow
c) White
d) Grey

Answer 139

a) Black