# Heat Transfer MCQ Questions & Answers

Heat Transfer MCQs : This section focuses on the "Heat Transfer". These Multiple Choice Questions (MCQs) should be practiced to improve the Heat Transfer skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.

Question 1

The steam ejector is used to

A. remove condensate from the steam pipelines.
B. create vacuum.
C. superheat the steam.
D. none of these.

Question 2

In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is

A. Minimum
B. Maximum
C. Zero
D. Infinity

Question 3

Kirchoff s law applies to __________ radiation.

A. Total
B. Monochromatic
C. Both A & B
D. Neither A nor B

Question 4

When water is kept in a very hot pan, the entire water heats up. Which mode of heat transfer is responsible for this?

A. Conduction
B. Convection
D. Convection along with radiation

Question 5

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

A. Reynolds
B. Nusselt
C. Grashoff
D. Both B & C

Question 6

Which of the following has the minimum absorptivity?

A. Aluminium foil
B. Coal dust
C. Refractory bricks
D. Iron plates

Question 7

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is

A. 1.66
B. 88.66
C. 3.66
D. Dependent on NRe only

Question 8

__________ paint has the maximum absorption coefficient.

A. Black
B. Yellow
C. White
D. Grey

Question 9

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

A. Flows through the tube
B. Flows outside the tubes
C. Can flow either inside or outside the tubes
D. Should not be used as it gives very high pressure drop

Question 10

Pick out the correct equation.

A. JH = (St)(Pr)2/3 = f/2
B. JH = (St)(Pr)1/3 = f/2
C. JH = (St)2/3(Pr) = f/2
D. JH = (St)1/3(Pr) = f/2

Question 11

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

A. Sum
B. Difference
C. Ratio
D. None of these

Question 12

In a single effect evaporator, the economy is

A. 1
B. < 1
C. > 1
D. None of these

Question 13

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.

Question 14

In natural convection heat transfer, the correlating parameter is the

A. Graetz number
B. Eckert number
C. Grashoff number
D. Bond number

Question 15

Which of the following is known as the dimensionless heat transfer coefficient?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Weber number

Question 16

Which has the lowest Prandtl number?

A. Liquid metal
B. Aqueous solution
C. Water
D. Lube oil

Question 17

It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is

A. > 0.75
B. < 0.75
C. < 0.50
D. < 0.25

Question 18

Mechanical recompression evaporation is used in the production of

A. Alcohol
B. Distilled water
C. Salt
D. Fruits jam

Question 19

An ejector is used to

A. Increase pressure
B. Increase temperature
C. Remove condensate
D. None of these

Question 20

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 of the above

Question 21

h.D/K is called the __________ number.

A. Nusselt
B. Peclet
C. Rayleigh
D. Grashoff

Question 22

Absorptivity and refletivity of a perfect black body are respectively

A. 1 and 0
B. 0 and 1
C. 1 and ?
D. 0 and 0.5

Question 23

A hot liquid is kept in a big room. The logorithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an

A. Ellipse
B. Straight line
C. Parabola
D. Circular arc

Question 24

For solids and liquids, specific heat

A. depends on the process
B. is independent of the process
C. may or may not depend on the process
D. none of the mentioned

Question 25

Steam is routed through the tube in case of a __________ evaporator.

B. Horizontal tube
C. Short tube vertical
D. Long tube vertical

Question 26

Which of the following has the highest thermal conductivity?

A. Brick
B. Air
C. Water
D. Silver

Question 27

Low thermal conductivity of heat insulating materials is due to its

A. Dense structure
B. High proportion of air space
C. High specific heat
D. None of these

Question 28

Pick out the wrong statement.

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

Question 29

In Fourier's law, the proportionality constant is called the

A. Heat transfer co-efficient
B. Thermal diffusivity
C. Thermal conductivity
D. Stefan-Boltzman constant

Question 30

Nusselt number is the ratio of the temperature gradient at the wall to

A. Temperature difference
B. Heat flux
C. That across the entire pipe
D. None of these

Question 31

For a laminar flow of fluid in a circular tube, 'h₁' is the convective heat transfer co-efficient at velocity 'V₁'. If the velocity is reduced by half and assuming the fluid properties are constant, the new convective heat transfer co-efficient is

A. 1.26 h₁
B. 0.794 h₁
C. 0.574 h₁
D. 1.741 h₁

Question 32

In sub-cooled boiling,

A. Temperature of the heating surface is less than the boiling point of the liquid
B. Temperature of the heating surface is more than the boiling point of the liquid
C. Bubbles from heating surface are absorbed by the mass of the liquid
D. Very large vapour space is necessary

Question 33

With increase in temperature, the total emissivity of conductors

A. Increases
B. Decreases
C. Remains same
D. Decreases linearly

Question 34

Radiator of an automobile engine is a __________ type of heat exchanger.

A. Co-current
B. Cross-current
C. Counter-current
D. Direct contact

Question 35

A composite wall consists of two plates A and B placed in series normal to the flow of heat. The thermal conductivities are kA and kB and the specific heat capacities are CPA and CPB for plates A and B respectively. Plate B has twice the thickness of plate A. At steady state, the temperature difference across plate A is greater than that across plate B, when

A. CPA > CPB
B. CPA < CPB
C. KA < 0.5kB
D. KA>2 kB

Question 36

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

Question 37

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

A. Q ∝ T²
B. Q ∝ T⁴
C. Q ∝ T³
D. None of these

Question 38

Graetz number is given by

A. mCp/kL
B. kL/mCp
C. mCp/kμ
D. kμ/mCp

Question 39

Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re0.8 . Prn, is not valid, if the value of

A. N = 0.4 is used for heating
B. N = 0.3 is used for cooling
C. Reynolds number for the flow involved is > 10000
D. Reynolds number for the flow involved is < 2100

Question 40

The non-dimensional temperature gradient in a liquid at the wall of a pipe is the

A. Heat flux
B. Nusselt number
C. Prandtl number
D. Schmidt number

Question 41

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

Question 42

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

A. Steel
B. Petrol
C. Air
D. All of the above

Question 43

Product of Grashof and Prandtl is known as?

A. Peclet number
B. Biot number
C. Rayleigh number
D. Reynolds number

Question 44

What is the emissivity of a black body?

A. 1
B. 0
C. 0.9
D. 0.5

Question 45

Heat transfer by natural convection is enhanced in system with

A. High viscosity
B. High co-efficient of thermal expansion
C. Low temperature gradients
D. Low density change with temperature

Question 46

The equivalent diameter for the annulus of a double pipe heat exchanger, whose inner pipe has fins on the outside is __________ compared to the same size pipes without fins.

A. More
B. Less
C. Same
D. Unpredictable

Question 47

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

Question 48

Fruit juice (a heat sensitive material) can be concentrated in a __________ evaporator.

A. Long tube
B. Falling film
C. High pressure
D. None of these

Question 49

The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the

A. Solution has an elevation of boiling point
B. Evaporators operate under vacuum
C. Evaporators opreate at atmospheric pressure
D. None of these

Question 50

Heat transfer rate per unit area is called

A. Thermal conductivity
B. Heat flux
C. Heat transfer co-efficient
D. Thermal diffusivity

Question 51

The transfer of heat between two bodies in direct contact is called

B. convection
C. conduction
D. none of the mentioned

Question 52

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

A. J/m²°K
B. W/m²°K
C. W/m°K
D. J/m°K

Question 53

The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.

A. Viscosity
B. Density
C. Thermal conductivity
D. Corrosive nature

Question 54

Wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature. This is __________ law.

A. Stefan's
B. Dalton's
C. Wien's
D. Kirchoffs

Question 55

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

Question 56

Value of Prandtl number for water ranges from

A. L to 2
B. 5 to 10
C. 100 to 500
D. 1000 to 2000

Question 57

The maximum heat transfer co-efficient from steam heating will be attained when the steam is

A. Supersaturated
B. Saturated
C. Wet
D. None of these

Question 58

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

Question 59

Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping

A. Both the tube sheets fixed
B. Both the tube sheets floating
C. The top tube sheet floating and bottom tube sheet fixed
D. The top tube sheet fixed and the bottom tube-sheet floating

Question 60

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

Question 61

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

Question 62

Tube expansion allowances exist in __________ heat exchanger.

A. Multipass fixed tube sheet
B. U-tube
C. Single pass fixed tube sheet
D. None of these

Question 63

Boiling of milk in an open vessel is an example of __________ boiling.

A. Film
B. Sub-cooled
C. Saturated nucleate
D. None of these

Question 64

In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat exchanger.

A. Once
B. Twice
C. Thrice
D. Four times

Question 65

A concentric double pipe heat exchanger as compared to the shell and tube heat exchanger for the same heat load requires

A. Less heating surface
B. More space
C. Lower maintenance cost
D. None of these

Question 66

In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid

A. Varies directly as the area and the LMTD
B. Directly proportional to LMTD and inversely proportional to the area
C. Varies as square of the area
D. None of these

Question 67

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

A. Conduction
B. Natural convection
C. Forced convection

Question 68

For a counter current heat exchanger with Tih = 80°C, T°c = 60°C, T°h = 50°C and Tic = 30°C, and the temperature difference between the two streams being the same everywhere along Z, the direction of flow of hot fluid. The temperature profile should satisfy

A. d²T/dZ² > 0
B. d²T/dZ² = 0
C. d²T/dZ² < 0
D. dT/dZ = 0

Question 69

A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun?

A. Yellow paint
B. White paint
C. Black paint
D. Grey paint

Question 70

Thermal conductivity of a conducting solid material depends upon its

A. temperature
B. porosity
C. both (a) & (b)
D. neither (a) nor (b)

Question 71

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

Question 72

The rate of heat transfer is a product of overall heat transfer co-efficient, the difference in temperature and the

A. Heating volume
B. Heat transfer area
C. Nusselt number
D. None of these

Question 73

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

Question 74

Loss of heat from untagged steam pipe to the ambient air is by

A. Conduction
B. Convection
D. All of the above

Question 75

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

A. 0.5
B. < 0.5
C. > 0.6
D. < 0.1

Question 76

Trap is used to remove __________ from steam pipe lines.

A. Steam
B. Condensate
C. Non-condensables
D. None of these

Question 77

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

Question 78

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.

Question 79

Maximum heat transfer rate is achieved in __________ flow.

A. Co-current
B. Counter-current
C. Turbulent
D. Laminar

Question 80

The purpose of floating head in a heat exchanger is to

A. Avoid buckling of tubes
B. Provide support for tubes
C. Decrease the pressure drop
D. Facilitate its lengthening, if needed

Question 81

In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of

A. Concentrations
B. Chemical potentials
C. Activity co-efficients
D. Mass transfer co-efficients

Question 82

Pick out the wrong statement.

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

Question 83

An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is

A. 4000
B. 9000
C. 4600
D. 3000

Question 84

Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low

A. Hardness
B. Dissolved soilds content
C. Suspended solids content
D. All of the above

Question 85

Sensible heat absorbed by 1 lb of water when it is heated from 32 to 212°F may be around __________ BTU.

A. 180
B. 970
C. 3.97
D. Data insufficient, can

Question 86

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

A. Continues to increase
B. Continues to decrease
C. Goes through a minimum
D. Goes through a maximum

Question 87

For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of

A. 1
B. 1.74
C. 6.1
D. 37

Question 88

Ratio of molecular diffusivity to thermal diffusivity is also known as?

A. Biot number
B. Prandtl number
C. Rayleigh number
D. Biot number

Question 89

In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is

A. ∞
B. 0
C. Equal to the difference between hot and cold fluids inlet temperature
D. Equal to the difference between hot fluid inlet temperature and cold fluid outlet temperature

Question 90

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

A. Strouhal number
B. Sherwood number
C. Euler number
D. Grashoff number

Question 91

The value of Stefan-Boltazman constant in SI unit is

A. 5.6697 x 10-8W/m².°K4
B. 0.1714 x 10-8W/m².°K4
C. 5.6697 x 10-8kcal/m² . °K4
D. 0.1714 x 10-8kcal/m². °K4

Question 92

Which of the following is the most widely used heat insulating material for pipelines carrying steam?

A. Tar dolomite bricks followed by asbestos
B. Fireclay refractory followed by aluminium sheet
C. Cotton followed by aluminium foil
D. 85% magnesia cement and glass wool

Question 93

Dropwise condensation is promoted on a/an __________ surface.

A. Glazed
B. Oily
C. Coated
D. Smooth

Question 94

Overall heat transfer co-efficient of a particular tube is U₁. If the same tube with some dirt deposited on either side has coefficient U₂, then

A. U₁ = U₂
B. U₂ > U₁
C. U₁ > U₂
D. U₁ = dirt factor - U₂

Question 95

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

Question 96

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

Question 97

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest ?

A. Cube
B. Plate
C. Sphere
D. All of the above

Question 98

Agitated film evaporator is suitable for concentrating __________ liquids.

A. Foaming
B. Viscous
C. Very thin
D. Corrosive

Question 99

Intermittant tube cleaning is possible to be done in case of a __________ evaporator.

B. Horizontal tube
C. Calendria
D. None of these

Question 100

A single pass air heater is connected to a two pass unit. For the air flow rate and other conditions remaining the same, the film heat transfer co-efficient for air will vary in the ratio of

A. 2
B. 20.8
C. 20.2
D. 20.5

Question 101

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

Question 102

Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be

A. 0.35
B. 0.45
C. 0.55
D. 0.85

Question 103

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

Question 104

For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would

A. Decrease
B. Increase
C. First decrease and then increase
D. First increase and then decrease

Question 105

What is the expression for heat current? Q is heat, t is time, T is temperature.

A. ΔQ/Δt
B. ΔQ/ΔT
C. ΔT/Δt
D. ΔQ/ΔTΔt

Question 106

When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is

A. Free convection
B. Entry length problem in laminar forced conduction (developing thermal boundary layer)
C. Mixed convection (both free and forced)
D. Forced convection

Question 107

Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the

A. Surrounding temperature
B. Average temperature of the fin
C. Temperature of the fin end
D. Constant temperature equal to that of the base

Question 108

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

Question 109

The statement that "maximum wavelength of radiation is inversly proportional to the temperature" is __________ law.

A. Stefan-Boltzman's
B. Planck's
C. Wien's displacement
D. None of these

Question 110

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 of the above

Question 111

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

A. 1
B. >1
C. < 1
D. 0.1

Question 112

For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is

A. 3
B. 0.33
C. 1
D. 1.33

Question 113

A wall has two layers of materials A and B; each made of a different material. Both the layers have the same thickness. The thermal conductivity of materialA is twice that of B. Under the equilibrium, the temperature difference across the wall is 36°C. The temperature difference across the layer A is __________ °C.

A. 6
B. 12
C. 18
D. 24

Question 114

Dropwise condensation occurs on __________ surfaces.

A. Clean and dirt free
B. Smooth clean
C. Contaminated cooling
D. Polished

Question 115

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

Question 116

Heat flux, as defined in heat flow is analogous to __________ in electricity flow.

A. Current
B. Voltage
C. Resistance
D. None of these

Question 117

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

Question 118

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

A. IR
B. I2R
C. IR2
D. I2R2

Question 119

Which of the following has maximum thermal conductivity?

A. Iron
B. Coal
C. Nitrogen
D. Tar

Question 120

Harmonic mean temperature difference is given by

A. √(ΔT₁ . ΔT₂)
B. 2.(ΔT₁ . ΔT₂)/(ΔT₁ + ΔT₂)
C. 2.(ΔT₁ . ΔT₂)(ΔT₁ - ΔT₂)
D. (ΔT₁ - ΔT₂)/(ΔT₁ . ΔT₂)

Question 121

Latent heat is taken at

A. constant temperature
B. constant pressure
C. both of the mentioned
D. none of the mentioned

Question 122

Double pipe heat exchangers are used

A. When heat transfer area required is very high
B. When heat transfer area required is very low, i.e (100-200 ft²)
C. Because it occupies less floor area
D. Because it is less costly

Question 123

For a liquid in laminar flow through a very long tube, when the exit fluid temperature approaches the wall temperature, the equation to be used is

A. Nu = 0.023 Re0.8 . Pr0.4
B. Nu = Gz
C. Nu = Gz
D. Nu = 2Gz0.5

Question 124

Walls of a cubical oven are of thickness l, and they are made of material of thermal conductivity k. The temperature inside the oven is 100°C and the inside heat transfer co-efficient is 3k/l. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?

A. 35.5
B. 43.75
C. 81.25
D. 48.25

Question 125

LMTD for evaporators & condensers for a given terminal parameters & set of conditions for counterflow is equal to that for parallel flow. In such heat exchangers, with one of the fluids condensing or evaporating, the surface area required is the least in the __________ flow.

A. Parallel
B. Mixed
C. Counterflow
D. Same in either A, B or C

Question 126

In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m².s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m²/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is

A. 2000
B. 4000
C. 5000
D. 6000

Question 127

What is the net amount of energy per unit time being received by a body having a temperature of 40 °C in a surrounding of 60°C? (The surface area of body = 2m2, σ = 5.67*10-8W/ m2K4 & emissivity of 0.4).

A. 122.4W
B. 0.47W
C. 33W
D. 86W

Question 128

Prandtl number is the reciprocal of

A. Thermal diffusivity/Momentum diffusivity
B. Thermal diffusivity x Momentum
C. Thermal diffusivity x Mass diffusivity
D. Mass diffusivity x Momentum diffusivity

Question 129

In a heat exchanger, one transfer unit means

A. A section of the exchanger in which change in temperature of one stream equals the average driving force in the section
B. The size of the exchanger in which heat transfer rate is 1 kcal/hr
C. Both A and B
D. None of these

Question 130

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

A. Double pipe
B. Plate fine
C. Series and parallel set of shell and tube
D. None of these

Question 131

The separation of liquid droplets from the vapor is done by a/an __________ , in the evaporators.

A. Steam ejector
B. Entrainment separator
C. Compressor
D. Vacuum pump

Question 132

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.

Question 133

The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in lminar zone is related as

A. Ha = 0.8hL
B. Ha = 2hL
C. Ha = hL
D. Ha= 5hL

Question 134

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

A. Gases
B. Solids
C. Liquids
D. Both B and C

Question 135

A steel and a copper bar are joined end to end. The area of the steel bar is half the area of the copper bar. Their lengths are equal to 10cm each. Temperature of free ends of steel & copper rod are 0°C & 100°C respectively. KS = 50 J/smK & KC =384 J/smK. Calculate equivalent thermal conductivity of the combined bar.

A. 63°C
B. 63K
C. 336°C
D. 36K

Question 136

Asymptotic conditions is reached, when for a fluid flowing in laminar flow through a long tube

A. Exit-fluid temperature > wall temperature
B. Exit fluid temperature < wall temperature
C. Exit fluid temperature = wall temperature
D. Graetz number > 100

Question 137

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

Question 138

Heat exchangers operating, when the asymptotic range is reached,

A. Provide very large heat transfer co-efficient
B. Results in making part of the heating surface inactive
C. Results in abruptly increased velocity
D. None of these

Question 139

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

A. 0°K
B. 0°C
C. 100°C
D. Room temperature

Question 140

The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K₀ + at. where, K is the thermal conductivity and T is the temperature (in °K). The units of 'a' in SI system will be

A. W/m.k
B. W/m
C. W/m.k²
D. None, A is just a number

Question 141

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.

Question 142

__________ paint has the minimum absorption co-efficient.

A. Black
C. Grey
D. Light cream

Question 143

Prandtl number for most of dry gases is about

A. 0.001
B. 0.72
C. 70
D. 150

Question 144

A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,

A. The cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant
B. Both the spheres will emit equal amount of radiation per unit time in the beginning
C. Both will absorb equal amount of radiation from the surrounding in the beginning
D. Both B & C

Question 145

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

Question 146

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

Question 147

Multiple effect evaporators ar used to

A. Increase the steam economy & decrease the capacity
B. Increase the steam economy & the capacity
C. Decrease the steam economy & the capacity
D. Decrease the steam economy & increase the capacity

Question 148

(NGr x NPr) is called the __________ number.

A. Graetz
B. Reyleigh
C. Nusselt
D. Stanton

Question 149

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

A. 1
B. 10
C. 20
D. 30

Question 150

Which of the following is true?

A. latent heat of fusion is not much affected by pressure
B. latent heat of vaporization is highly sensitive to pressure
C. both of the mentioned
D. none of the mentioned

Question 151

Select the correct statement.

A. Radiation doesn’t require any medium
B. Convection involves heat transfer by vibration of particles at their position
C. Conduction involves movement of particles to transfer heat
D. Radiation is responsible for heat of gas flame heating the cooking pan

Question 152

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

A. Twice
B. Four times
C. Square root of
D. Square of

Question 153

Steam traps are provided in steam carrying pipelines to

A. Condense steam
B. Release excess steam pressure by bleeding steam
C. Remove condensate and inert gases
D. None of these

Question 154

In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is

A. 40.5
B. 34.4
C. 26.8
D. 25

Question 155

Fouling factor for a heat exchanger is given by (where, U₁ = heat transfer co-efficient of dirty surface U₂ = heat transfer co-efficient of clean surface)

A. U₁ - U₂
B. 1/U₁ - 1/U₂
C. 1/U₂ - 1/U₁
D. U₂ - U₁

Question 156

Rate of crystallisation does not depend upon the

A. Extent of supersaturation
B. Turbulence within the solution
C. Number and active surface area of the crystals
D. None of these

Question 157

Calburn analogy is applicable for the value of Prandtl number from

A. 0.001 to 1
B. 0.6 to 120
C. 0.5 to 5
D. 120 to 400

Question 158

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

A. White & rough
B. Black & rough
C. White & polished
D. Black & polished

Question 159

Viscous & heat sensitive liquids are concentrated in __________ evaporators.

A. Open pan
B. Long tube
C. Agitated film
D. None of these

Question 160

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 of the above

Question 161

Pick out the wrong statement:

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

Question 162

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

A. t⁴
B. T⁴
C. 1/t⁴
D. 1/T⁴

Question 163

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

A. Reduce the capacity
B. Reduce the economy
C. Increase the economy
D. None of these

Question 164

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

Question 165

The Stefan-Boltzman constant depends on the

A. Medium
B. Temperature
C. Surface
D. None of these

Question 166

Fresh orange juice contains 12% (by weight) solids and the rest water 90% of the fresh juice is sent to an evaporator to remove water and subsequently mixed with the remaining 10% of fresh juice. The resultant product contains 40% solids. The kg of water removed from 1 kg fresh juice is

A. 0.4
B. 0.5
C. 0.6
D. 0.7

Question 167

Maximum heat transfer rate is obtained in __________ flow.

A. Laminar
B. Turbulent
C. Creeping
D. Transition region

Question 168

The absorptivity of a body is equal to its emissivity

A. At a particular temperature
B. For circular bodies
C. Under thermal equilibrium
D. None of these

Question 169

Which of the following has the minimum thermal conductivity?

A. Nitrogen
B. Steel
C. Carbon black
D. Tar

Question 170

Fourier's law of heat conduction applies to __________ surfaces.

A. Isothermal
B. Non-isothermal
C. Both A and B
D. Neither A and B

Question 171

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

Question 172

Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger?

A. Corrosiveness
B. Fouling characteristic
C. Viscosity
D. None of these

Question 173

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

A. Abundance & high heat capacity
B. Low density
C. Low viscosity
D. High fluidity

Question 174

Pick out the wrong statement.

A. Reciprocal of the resistance to heat flow is called thermal conductance
B. Unit of thermal conductance is W/°K
C. Thermal conductance of a wall of thickness
D. None of these

Question 175

Kirchoff s law applies to __________ radiation.

A. total
B. monochromatic
C. both (a) & (b)
D. neither (a) nor (b)

Question 176

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

A. Wavelength of radiation
B. Surface temperature of the body
C. Nature of the surface
D. Shape and porosity of the body

Question 177

The driving potential for the crystal growth during crystallisation is the __________ of the solution.

A. Concentration
B. Viscosity
C. Super-saturation
D. Density

Question 178

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

A. A higher capacity
B. A lower capacity
C. Lower economy
D. None of these

Question 179

Heat and work are

A. path functions
B. inexact differentials
C. depend upon the path followed
D. all of the mentioned

Question 180

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

A. smaller than
B. greater than
C. equal to
D. not related with

Question 181

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

A. Thermal conductivity
B. Thickness
C. Temperature difference
D. Heat transfer area

Question 182

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

A. Kirchoffs
B. Planck's
C. Wien's displacement
D. Stefan-Boltzman

Question 183

Which of the following has the lowest Prandtl number?

A. Molten sodium (a coolant used in fast breeder reactor)
B. Water
C. Transformer oil
D. Dilute H₂SO₄

Question 184

The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body)

A. αT
B. α 1/T
C. α T⁴
D. Independent of T

Question 185

Ratio of inertia to viscous forces is known as?

A. Stanton number
B. Prandtl number
C. Rayleigh number
D. Reynolds number

Question 186

Two spheres, A & B, are made up of the same material. The radius of A is twice that of B, while the temperature of A is half that of B. What is their ratio of energy emitted per unit time (EA : EB)?

A. 1
B. 1/4
C. 1/2
D. 1/16

Question 187

Prandtl and Reynold's analogies are identical for Prandtl number value of

A. 0
B. 0.5
C. 1
D. 5

Question 188

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

A. Heat transfer co-efficient are high
B. There is no risk of contamination
C. There is no mist formation
D. Cost of equipment is lower

Question 189

Which is the most suitable for the concentration of foamy & frothy liquors?

A. Agitated film evaporator
B. Long tube vertical evaporator
C. Open pan evaporator
D. None of these

Question 190

Hot water (0.01 m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m3/min) of density 800 kg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately

A. 32
B. 37
C. 45
D. 50

Question 191

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

A. D/5 and D
B. D/2 and 2 D
C. D/4 and 2 D
D. D and 2 D

Question 192

Pick out the wrong statement.

A. In process heat exchangers, saturated steam is preferred over the superheated steam
B. The maximum is the emissive power of a surface at a temperature T₁ occurs at a wavelength of λ₁. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelengt
C. When a vertical plate is heated in infinite air environmental under natural convection conditions, the velocity profile in air, normal to the plate, exhibits a maximum
D. A body at 925 K emits an energy of 1.42 x 10¹¹σW/m² (σ is the Stefan-Boltzman constant) in the wavelength band between 3 μm to 4 μm. The fraction of this energy in the total energy emitted over

Question 193

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

Question 194

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'

Question 195

In forced convection, the heat transfer depends on

A. Re, Pr
B. Re, Gr
C. Mainly Gr
D. Re only

Question 196

If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface tempeature follows __________ law.

A. Parabolic
B. Hyperbolic
C. Linear
D. Logarithmic

Question 197

Thermal diffusivity of a material

A. Has the unit m² /sec
B. Is defined as K/ρ . Cp
C. Is the ratio of thermal conductivity to thermal capacity
D. All of the above

Question 198

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

Question 199

If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.

A. Increase
B. Decrease
C. Not affect
D. Increase the condensing film co-efficient as well as

Question 200

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

Question 201

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

Question 202

Nusselt number is the ratio of the

A. Temperature gradient of the wall to that across the entire pipe
B. Temperature difference to the temperature gradient at the wall
C. Heat flux at the wall to that across the entire pipe
D. None of these

Question 203

Pick out the wrong statement.

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

Question 204

The thermal boundary layer at NPr > 1

A. Is thicker than hydrodynamic boundary layer
B. Is thinner than hydrodynamic boundary layer
C. And the hydrodynamic boundary layer are identical
D. Disappears

Question 205

Baffle spacing

A. Is not the same as baffle pitch
B. Should be less than one fifth the diameter of the shell
C. Should be less than the inside diameter of the shell
D. None of these

Question 206

In a shell and tube heat exchanger, floating head is used for

A. Large temperature differentials
B. High heat transfer co-efficient
C. Low pressure drop
D. Less corrosion of tubes

Question 207

Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are clean and non-fouling?

A. Square pitch
B. Triangular pitch
C. Diagonal square pitch
D. None of these

Question 208

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

A. Viscous
B. Elastic
C. Inertial
D. None of these

Question 209

Boiling point elevation of a solution of NaOH

A. Increases rapidly with temperature rise
B. Is almost independent of temperature
C. Is almost independent of pressure
D. Both B and C

Question 210

Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface?

A. Liquid density
B. Liquid viscosity
C. Hot surface temperature
D. Interfacial tension

Question 211

Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is

A. Vertical heat exchanger with steam on tube side
B. Vertical heat exchanger with steam on shell side
C. Horizontal heat exchanger with steam on tube side
D. Horizontal heat exchanger with steam on shell side

Question 212

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

Question 213

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).

Question 214

In the equation, dQ=TdX

A. dQ is an inexact differential
B. dX is an exact differential
C. X is an extensive property
D. all of the mentioned

Question 215

A perfect black body is a perfect __________ of radiation.

A. Absorber
B. Emitter
C. Both A & B
D. Neither A nor B

Question 216

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

Question 217

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

Question 218

Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer.

A. Grashoff
B. Reynolds
C. Both A & B
D. Prandtl & Grashoff

Question 219

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.

Question 220

A composite flat wall of a furnace is made of two materials 'A' and 'B'. The thermal conductivity of 'A' is twice of that of material 'B', while the thickness of layer of 'A' is half that of B. If the temperature at the two sides of the wall are 400 and 1200°K, then the temperature drop (in °K) across the layer of material 'A' is

A. 125
B. 133
C. 150
D. 160

Question 221

Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the

A. Maximum resistance in the series
B. Sum of all resistances
C. Average of all resistances
D. Minimum resistance presents in the series

Question 222

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.

Question 223

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

A. Approach
B. Log mean temperature difference
C. Arithmetic mean temperature difference
D. Geometric mean temperature difference

Question 224

Duhring's plot' is of use in

A. Extractive distillation
B. Evaporation
C. Leaching
D. Absorption

Question 225

Boiling point elevation for a strong and concentrated solution is found by Duhring's rule, which states that at the same pressure, the boiling point of a solution is a linear function of the __________ of pure water.

A. Boiling point
B. Dynamic viscosity
C. Kinematic viscosity
D. Density

Question 226

One kilogram of water at 0°C is changed to superheated steam of one atm pressure and 300° C. The major heat consumption in the process will be to

A. Heat the water from 0°C to 100°C
B. Evaporate the water
C. To superheat the steam
D. Data insufficient, can

Question 227

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

A. Increasing temperature
B. Decreasing temperature
C. Decreasing Reynolds number
D. None of these

Question 228

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

A. Lewis relationship
B. Nusselt number
D. Froude number

Question 229

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

A. Fourier's law
B. Newton's law of cooling
C. Fick's law
D. None of these

Question 230

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 of the above

Question 231

jH factor for heat transfer depends upon the __________ number.

A. Biot
B. Nusselt
C. Reynolds
D. Prandtl

Question 232

Ratio of buoyancy to viscous forces is known as?

A. Prandtl number
B. Grashof number
C. Colburn factor
D. Nusselt number

Question 233

A __________ evaporator employs an annular downtake.

B. Horizontal
C. Long tube vertical
D. None of these

Question 234

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

A. D0.8
B. D-0.2
C. D-1
D. D-1.8

Question 235

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

A. Bleed point
B. Vent
C. Catchall
D. Baffle

Question 236

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

A. J/M2°K
B. W/m2°K
C. W/m°K
D. J/m°K

Question 237

Mode of heat transfer involved in the cooling of air cooled internal combustion engine is

A. Conduction
B. Natural convection
C. Forced convection
D. None of these

Question 238

The purpose of providing expansion bellows in the shell of tubular exchanger is to

A. Increase the heating load
B. Impart structural strength
C. Account for the uneven expansion of shell and tube bundles
D. Facilitate increase of shell length, if needed

Question 239

Planck's distribution law is valid for __________ bodies.

A. Black
B. White
C. Coloured
D. All of the above

Question 240

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)

Question 241

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

A. Exothermic
B. Mildly endothermic
C. Highly endothermic
D. None of these

Question 242

A body cools down from 75°C to 70°C in 10 minutes. It will cool down from 70° C to 65° C in __________ minutes.

A. 10
B. >10
C. <10
D. Either B or C, depends on the mass of the body

Question 243

Unsteady state heat conduction occurs, when

A. Temperature distribution is independent of time
B. Temperature distribution is dependent on time
C. Heat flows in one direction only
D. Three dimensional heat flow is concerned

Question 244

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

A. Decreases
B. Increases
C. Increases exponentially
D. Remains unaffected

Question 245

Stefen's block body radiation law can also be derived from __________ law.

A. Kirchoffs
B. Planck's
C. Fourier's
D. None of these

Question 246

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

A. Zero
B. Unity
C. Same for all wavelengths
D. Different for all wavelengths

Question 247

Air is best heated with steam in a heat exchanger of

A. shell and tube type
B. plate type
C. double pipe type with fin on steam side
D. double pipe type with fin on air side

Question 248

The units of resistance to heat transfer is

A. J.m⁻².K⁻¹
B. J.m⁻¹.K⁻¹
C. W.m⁻².K⁻¹
D. W⁻¹m²K

Question 249

Steam economy in case of a triple effect evaporator will be

A. 1
B. < 1
C. > 1
D. Between 0 and 1

Question 250

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

A. 2f
B. f
C. f/2
D. f/4

Question 251

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

A. Conduction
B. Convection
D. Both A & C

Question 252

The inner wall of a furnace is at a temperature of 700°C. The composite wall is made of two substances, 10 and 20 cm thick with thermal conductivities of 0.05 and 0.1 W.m-1.°C-1 respectively. The ambient air is at 30°C and the heat transfer co-efficient between the outer surface of wall and air is 20 W.m⁻².°C-1. The rate of heat loss from the outer surface in W.m-2is

A. 165.4
B. 167.5
C. 172.5
D. 175

Question 253

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).

Question 254

(Cp . μ)/K is termed as the __________ number.

A. Grashoff
B. Nusselt
C. Prandtl
D. Stanton

Question 255

Heat flux is the time rate of heat transfer per unit

A. Length
B. Area
C. Volume
D. None of these

Question 256

A dephlegmator is a

A. Total condenser
B. Vacuum evaporator
C. Partial condenser
D. Double pipe heat exchanger

Question 257

A sphere of radius 'R₁' is enclosed in a sphere of radius 'R₂'. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is

A. 0
B. R₂/(R₁+R₂)
C. 1
D. (R₁/R₂)2

Question 258

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

A. Thermal boundary layer lies inside the concentration boundary layer
B. Concentration boundary layer lies inside the thermal boundary layer
C. Thermal & concentration boundary layers are of equal thickness
D. Hydrodynamic(i.e., momentum)boundary layer is thicker than the other two

Question 259

Pick out the wrong statement.

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

Question 260

It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is

A. 3.06 x l0⁵
B. 6.12 x 10⁵
C. 7.24 x 10⁵
D. 9.08 x 10⁵

Question 261

Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger?

A. Corrosiveness & fouling characteristics
B. Pressure
C. Viscosity
D. Density

Question 262

Choose the most important factor on which the heat conducted through a wall in a unit time will depend on?

A. Thickness of the wall
B. Area of the wall perpendicular to heat flow
C. Material of the wall
D. Temperature difference between the two surfaces of the wall

Question 263

A graph between __________ is called Wilson plot.

A. 1/U Vs . 1/v0.8
B. 1/v0.8 Vs . U
C. V0.8 Vs . U
D. 1/U Vs . 1/V

Question 264

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

Question 265

Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is

A. 0.1
B. >1
C. < 1
D. L

Question 266

Evaporation by thermocompression results in the

A. Saving of steam
B. Realisation of multiple effect economy in a single effect
C. Both A and B
D. None of these

Question 267

The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu α Re0.8, where, Nu is the Nusselt number and Re is the Reynolds number for the flow. Assuming that this relation is valid, the heat transfer co-efficient varies with the pipe diameter (D) as

A. (D)-1.8
B. (D)-0.2
C. (D)0.2
D. (D)1.8

Question 268

Ratio of rate of heat conduction to the rate of internal energy storage is in solid is known as?

A. Biot number
B. Drag coefficient
C. Eckert number
D. Fourier number

Question 269

For __________ Prandtl number values, the heat conduction will be negligible in the buffer zone.

A. Extremely low
B. Low
C. High
D. No

Question 270

If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will

A. Increase by 1.8 times
B. Decrease by 22
C. Increase by 216
D. Remain unchanged

Question 271

What is the thermal conductivity of a perfect heat insulator?

A. Zero
B. One
C. ∞
D. Between 0 and ∞

Question 272

Forced circulation evaporators are normally used for concentrating liquids having

A. Scaling characteristics
B. High viscosity
C. Both A & B
D. Neither A nor B

Question 273

For an ideal black body

A. absorptivity = 1
B. reflectivity = 1
C. emissivity = 0
D. transmissivity = 1

Question 274

Conductance is given by(where, x = thickness, A = heat flow area, K = thermal conductivity.)

A. X/KA
B. KA/x
C. K/Ax
D. A/Kx

Question 275

In the free convection regime of pool boiling, the heat flux is proportional to

A. Δt1/2
B. Δt2
C. Δt5/4
D. Δt

Question 276

In Biot number, the characteristic length used is the ratio of the __________ of the solid.

A. Volume to surface area
B. Perimeter to surface area
C. Surface area to volume
D. Surface area to perimeter

Question 277

The inside heat transfer co-efficient in case of turbulent flow of liquid in the tube side in a 1-2 shell and tube heat exchanger is increased by __________ times, when the number of tube passes is increased to 8.

A. 20.8
B. 40.8
C. 40.4
D. 20.4

Question 278

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

A. 2
B. 1-2
C. 4
D. 1-4

Question 279

Correction is applied to LMTD for __________ flow.

A. Parallel
B. Counter
C. Cross
D. None of these

Question 280

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

A. Baffle spacing & shell diameter
B. Tube diameter & pitch
C. Viscosity, density & mass velocity of shell side fluid
D. None of these

Question 281

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

Question 282

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

A. 0.5
B. 1
C. 1.5
D. 80

Question 283

The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy.

A. Colburn
B. Reynolds
C. Prandtl
D. None of these

Question 284

Multipass heat exchangers are used

A. Because of simplicity of fabrication
B. For low heat load
C. To obtain higher heat transfer co-efficient and shorter tube
D. To reduce the pressure drop

Question 285

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.

Question 286

Heat flow into a system is taken to be ____, and heat flow out of the system is taken as ____

A. positive, positive
B. negative, negative
C. negative, positive
D. positive, negative

Question 287

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

A. Nature of heating surface and distribution of bubbles
B. Surface tension of water
C. Viscosity of water
D. All of the above

Question 288

In a boiling curve, the peak heat flux is called the __________ point.

A. Nusselt
B. Leidenfrost
C. Boiling
D. Burnout

Question 289

Ratio of convection heat transfer to conduction is known as?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number

Question 290

Heat exchanger tubes are never made of

A. Plain carbon steel
B. Stainless steel
D. Copper

Question 291

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

A. Nucleate
B. Local
C. Pool
D. Saturated

Question 292

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.

Question 293

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

A. Lower tube side pressure drop
B. Lower shell side pressure drop
C. Higher tube side heat transfer co-efficient
D. Higher shell side heat transfer co-efficient

Question 294

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

A. 180
B. 970
C. 3.97
D. None of these

Question 295

What is the value of Wien’s constant?

A. 2.9*10-3mK
B. 2.9*10-4mK
C. 2.9*10-3cmK
D. 2.9*10-4cmK

Question 296

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

A. Lewis relationship
B. Nusselt number
D. Froude number

Question 297

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.

Question 298

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

Question 299

Viscosity of gases __________ with increase in temperature.

A. Increase very rapidly
B. Increase slowly
C. Decrease slowly
D. Remain unaffected

Question 300

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

Question 301

For concentrating an aqueous solution of a material like anhydrous Na₂SO₄, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator.

A. High pressure
B. Vacuum
C. Backward feed
D. None of these

Question 302

Reynold's analogy states that

A. Nst α f
B. Nst α NRe
C. NNu α f
D. NRe α f

Question 303

Pick out the wrong statement.

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

Question 304

The unit of heat transfer co-efficient is

A. BTU/hr. ft²°F
B. BTU/hr. °F. ft
C. BTU/hr. °F
D. BTU/hr. ft

Question 305

Corrosiveness of steam condensate is due to the presence of

A. CO₂
B. Dissolved O₂
C. Both A & B
D. Neither A nor B

Question 306

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

Question 307

A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m².K. The Biot number is

A. 5.6
B. 0.025
C. 3.5
D. 0.0035

Question 308

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)

Question 309

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

Question 310

If h₁ = inner film co-efficient and /h₂ = outer film co-efficient, then the overall heat transfer co-efficient is

A. Always less than h₁
B. Always between h₁ and h₂
C. Always higher than h₂
D. Dependent on metal resistance

Question 311

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

A. Tube side pressure drop and the heat transfer rate
B. Convective heat transfer co-efficient
C. Effective tube surface area for convective heat transfer
D. All of the above

Question 312

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

Question 313

Steam trap is used to

A. Condense the steam flowing in the pipeline
B. Remove water resulting from partial condensation of steam
C. Stop the supply of steam
D. None of these

Question 314

Crystal size in a continuous crystalliser depends upon the

A. Rate of heat transfer
B. Degree of turbulence
C. Degree of supersaturation
D. All of the above

Question 315

The Grashoff number is defined as the ratio of the

A. Buoyancy to inertial forces
B. Buoyancy to viscous forces
C. Inertial to viscous forces
D. Buoyancy to surface tension forces

Question 316

Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity?

A. Aluminium foil
B. Refractory bricks
C. Iron plate
D. Coke breeze

Question 317

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.

Question 318

The radiation heat flux from a heating element at a temperature of 800°C, in a furnace maintained at 300°C is 8 kW/m². The flux, when the element temperature is increased to 1000°C for the same furnace temperature is

A. 11.2 kW/m²
B. 12.0 kW/m²
C. 14.6 kW/m²
D. 16.5 kW/m²

Question 319

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

Question 320

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

A. K/h0
B. 2K/h0
C. hi/K
D. 2hi/K

Question 321

Multiple effect evaporation accounts for

A. Steam economy
B. Lower operating costs
C. Investment economy
D. None of these

Question 322

Heat transfer and work transfer are

A. boundary phenomena
B. energy interactions
C. energy in the transit
D. all of the mentioned

Question 323

(NRe.NPr)(D/L) is called the __________ number

A. Peclet
B. Stanton
C. Graetz
D. None of these

Question 324

Double pipe heat exchangers are preferably useful, when

A. High viscosity liquid is to be cooled
B. Requirement of heat transfer area is low
C. Overall heat transfer co-efficient is very high
D. A corrosive liquid is to be heated

Question 325

The thickness of condensate layer in filmwise condensation depends on the

A. Condensation rate
B. Surface configuration
C. Liquid flow rate from the surface
D. All of the above

Question 326

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

A. 1
B. > 1
C. < 1
D. Between 1 & 2

Question 327

In a shell and tube heat exchanger, the shell side fluid velocity can not be changed by changing the

A. Tube layout
B. Tube diameter
C. Tube pitch
D. No. of baffles

Question 328

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50°C in industrial practice mainly to avoid

A. Its evaporation loss
B. Excessive corrosion
C. Uneconomic LMTD
D. Decrease in heat exchanger efficiency

Question 329

For a perfectly transparent surface (like gases), the

A. Absorptivity = 0
B. Transmissivity = 1
C. Reflectivity = 0
D. All of the above

Question 330

At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical?

A. 1
B. < 1
C. > 1
D. None of these

Question 331

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

Question 332

The heat transfer co-efficient in film type condensation is __________ that for dropwise condensation.

A. Greater than
B. Lower than
C. Is same as
D. Half

Question 333

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

A. Wall or skin friction
B. Form friction
C. Both A and B
D. Turbulent flow

Question 334

During crystallisation, formation of crystal can occur in __________ solution only.

A. Saturated
B. Supersaturated
C. Undersaturated
D. All of the above

Question 335

Duhring rule is important in solving problems on

A. Distillation
B. Crystallisation
C. Evaporation
D. Humidification

Question 336

Open pan evaporators are preferred to be used, when the solution to be concentrated is

A. Scaling
B. Highly viscous
C. Corrosive
D. Salty

Question 337

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

A. Least at the inlet of the first effect
B. Least at the outlet of the last effect
C. Highest at the inlet of the last effect
D. Highest at the outlet of the last effect

Question 338

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.

Question 339

Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for

A. Cube
B. Cylinder
C. Sphere
D. Equal for all the three

Question 340

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

A. Get economical temperature difference by using moderate pressure steam
B. Facilitate forward feeding in multiple effect evaporation
C. Concentrate heat sensitive materials
D. Achieve very high concentration of the final product

Question 341

In which mode of heat transfer, the Biot number is important?

A. Transient heat conduction
B. Natural convection
C. Forced convection

Question 342

Product of Prandtl number and Reynolds number is also known as?

A. Peclet number
B. Prandtl number
C. Rayleigh number
D. Biot number

Question 343

For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then

A. hf = hd
B. hf > hd
C. hf < hd
D. hf could be greater or smaller than hd

Question 344

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

Question 345

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)

Question 346

At a given temperature a body emits energy of a single wavelength corresponding to that temperature. True or False?

A. True
B. False

Question 347

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

Question 348

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

Question 349

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 tem
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

Question 350

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

Question 351

The steam ejector is used to

A. Remove condensate from the steam pipelines
B. Create vacuum
C. Superheat the steam
D. None of these

Question 352

Prandtl and Reynolds analogy are same, when Prandtl number is

A. 0.5
B. 1
C. > 2
D. 1.5

Question 353

Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is

A. Thin walled having the value of Ao Ai/< 2
B. Thick walled
C. Having the value of Ao/Ai > 2
D. Both B and C

Question 354

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

A. Infinity
B. Zero
C. Same as average heat transfer co-efficient for tube side
D. None of these

Question 355

Stefan-Boltzman law applies to __________ body.

A. Black
B. White
C. Grey
D. Any colour

Question 356

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

Question 357

Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is

A. 0.5
B. 2
C. 10
D. 100

Question 358

In SI units, thermal conductivity is expressed in

A. Watt/m.°K
B. Watt/m². °K
C. Watt/m². °K
D. Watt/m4. °K

Question 359

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

A. 1.5
B. 1
C. > 1
D. < 1

Question 360

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.

Question 361

In a single evaporator system, the steam economy __________ by creating vacuum in the evaporator.

A. Increases
B. Decreases
C. Remains constant
D. May increase or decrease, depends on the vacuum

Question 362

Film boiling is usually not desired in commercial equipments, because

A. The heat transfer rate is low in view of the large temperature drop
B. It is difficult to maintain
C. It is not economic
D. None of these

Question 363

Dropwise condensation of steam on cooling surface is promoted

A. An oily surface
B. When both the steam and the tube are clean
C. Only in presence of air
D. None of these

Question 364

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

Question 365

Small scale evaporation is done in a

A. Heat exchanger
B. Condenser
C. Multiple effect evaporator
D. Steam jacketed kettle

Question 366

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

Question 367

A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

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

Question 368

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

A. 25°C
B. 30°C
C. 35°C
D. 40°C

Question 369

The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m².K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m².K. The overall heat transfer co-efficient at this time is

A. 1200W/m².K
B. 894W/m².K
C. 333W/m².K
D. 287 W/m².K

Question 370

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

A. 0.5
B. 1
C. 0
D. 2

Question 371

Pick out the wrong statement.

A. In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2
B. Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number to Prandtl number
C. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger
D. Hot gases at moderate pressure are usually in the shell side of shell and tube heat exchangers. At higher pressure, however, it is customary to put gas in the tube side

Question 372

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

A. Nucleate
B. Pool
C. Low pressure
D. None of these

Question 373

Vent pipes are provided in a condenser to

A. Remove non-condensable gases
B. Purge the condenser
C. Facilitate easy cleaning of tubes
D. None of these

Question 374

A diathermaneous substance __________ the thermal radiation completely.

A. Absorbs
B. Reflects
C. Transmits
D. None of these

Question 375

Multiple effect evaporation is generally recommended, when the

A. Large scale evaporation of liquor is needed
B. Corrosive liquids are to be concentrated
C. Fuel is cheaply available
D. Evaporation on small scale is to be done

Question 376

Film condensation is promoted on a/an __________ surface.

A. Oily
B. Coated
C. Clean & smooth
D. Dirty

Question 377

Peclet number (Pe) is given by

A. Pe = Re.Pr
B. Pe = Re/Pr
C. Pe = Pr/Re
D. Pe = Nu.Re

Question 378

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

Question 379

Reason for operating an evaporator in multiple effect is to secure

A. Increased steam economy
B. Decreased steam consumption
C. Both A and B
D. Increased capacity

Question 380

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)

Question 381

Pick out the wrong statement.

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

Question 382

If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.

A. Hyperbolic
B. Parabolic
C. Linear
D. Logarithmic

Question 383

In a gas-liquid shell and tube heat exchanger, the

A. Presence of a non-condensible gas decreases the condensing film co-efficient
B. Gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature
C. Gases to be heated/cooled is normally routed through the shell side, because the corrosion caused by the cooling water or steam condensate remain localised to the tubes
D. All of the above

Question 384

Nucleate boiling is promoted

A. On polished surfaces
B. On rough surfaces
C. In the absence of agitation
D. None of these

Question 385

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).

Question 386

Removal of __________ heat is involved in the condensation of a vapor under saturated conditions.

A. Super
B. Sensible
C. Latent
D. Both B & C

Question 387

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

A. Keeping the heat transfer surface clean
B. Enhancing the fluid pumping rate
C. Increasing the tube length
D. None of these

Question 388

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

A. Δt
B. Δt²
C. Δt³
D. √Δt

Question 389

Kirchoff's law is applicable to

A. Monochromatic radiation only
B. Total radiation only
C. Both A and B
D. Only volumes and not to surfaces

Question 390

The transfer of heat between a wall and a fluid system in motion is called

B. convection
C. conduction
D. none of the mentioned

Question 391

__________ heat exchanger is used for chilling oil to be dewaxed.

A. U-tube
B. Double pipe
C. Fixed tube

Question 392

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

A. Boiling point (at the same pressure)
B. Viscosity
C. Density
D. Thermal conductivity

Question 393

Thermal diffusivity is the most important in heat transfer by

A. Conduction
C. Condensation
D. Natural convection

Question 394

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 of the above

Question 395

In a backward feed multiple effect evaporator

A. Feed is introduced in the first effect
B. Feed flows from low pressure to high pressure
C. No pumps are required between successive effects
D. None of these

Question 396

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

A. 3 x l05
B. 3 x l08
C. 3 x l010
D. 3 x l012

Question 397

Which of the following is known as the dimensionless heat transfer coefficient?

A. Friction factor
B. Grashof number
C. Nusselt number
D. Prandtl number

Question 398

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

A. Black & smooth
B. Black & rough
C. White & smooth
D. White & rough

Question 399

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. NPr1/3
C. NPr-1
D. NPr-1/3

Question 400

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

Question 401

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m² .°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

A. Higher condensing film co-efficient is desired
B. Condensate is corrosive in nature
C. Lower pressure drop through the exchanger is desired
D. Temperature of the incoming vapor is very high

Question 402

Thermal conductivity of a conducting solid material depends upon its

A. Temperature
B. Porosity
C. Both A & B
D. Neither A nor B

Question 403

Fourier's law applies to the heat transfer by

A. Convection
C. Conduction
D. All of the above

Question 404

To reduce the tube side pressure drop for the same flow rate, the heat exchanger recomended is

A. 1-2 heat exchanger
B. 1-1 heat exchanger
C. 3-2 heat exchanger
D. 2-4 heat exchanger

Question 405

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

A. Same
B. Different
C. Never different
D. Linearly related

Question 406

Heat sensitive materials can be concentrated in an evaporator employing

A. Vacuum
B. High pressure
C. High residence time
D. None of these

Question 407

Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is

A. 0.2
B. 0.4
C. 0.6
D. 0.8

Question 408

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

Question 409

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

A. Increased economy
B. Decreased economy
C. Lower capacity
D. No effect on economy

Question 410

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

Question 411

__________ chart is known as transient heat conduction chart.

A. Dirhing's
B. Heisler's
C. Mollier's
D. Cox

Question 412

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

A. 25°C
B. 30°C
C. 35°C
D. 40°C

Question 413

Steady state one dimensional heat flow by conduction as given by Fourier's low does not assume that

A. There is no internal heat generation
B. Boundary surfaces are isothermal
C. Material is anisotropic
D. Constant temperature gradient exists

Question 414

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

A. Peclet
B. Prandtl
C. Stanton
D. Nusselt

Question 415

Pick out the wrong statement.

A. Heat transfer by radiation can not occur across an absolute volume
B. In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bundle between baffles
C. Propagation velocity for travel of heat radiation through vacuum is equal to the velocity of the light
D. The amount of heat involved in the condensation or vaporisation of 1 kg of a fluid is the same

Question 416

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

Question 417

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

Question 418

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

Question 419

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

Question 420

Pick out the wrong statement.

A. In case of heat transfer by purely forced convection, GR/Re2 ≤ 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.

Question 421

Ratio of pressure drop for internal flow through ducts is known as?

A. Friction factor
B. Grashof number
C. Colburn factor
D. Nusselt number

Question 422

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. d2
D. d1.5

Question 423

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.

Question 424

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

Question 425

Overall heat transfer co-efficient for cooling of hydrocarbons by water is about

A. 50 -100 Kcal/hr.m².°C
B. 50 -100 W/m² . °K
C. 50 -100 BTU/hr. ft.2°F
D. 1000 - 1500 BTU/hr. ft.2°F

Question 426

The equation, Nst = f/2, is the __________ analogy.

A. Colburn
B. Reynolds
C. Prandtl
D. None of these

Question 427

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

A. 0.72
B. 4.364
C. 18
D. 83

Question 428

Temperature profile in steady state heat transfer is

A. Asymptotic
B. Hyperbolic
C. Parabolic
D. Linear

Question 429

Natural convection is characterised by

A. Grashhoff number
B. Peclet number
C. Reynolds number
D. Prandtl number

Question 430

Sensible heat of hot industrial flue gases can not be recovered by a/an

A. Economiser
B. Regenerator
C. Ceramic recuperator
D. None of these

Question 431

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

Question 432

Quantitatively heat conduction can be described as?

A. Heat flow for a given temperature difference
B. Time rate of heat flow for a given temperature difference
C. Temperature difference caused due to heat flow per unit time
D. Temperature difference per unit quantity of heat transferred

Question 433

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

Question 434

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

Question 435

The sun emits light having maximum intensity at a wavelength 468nm. Assume emissivity of sun is 1. Calculate its surface temperature. σ= 5.67*10-8W/m2K4.

A. 6800K
B. 3400K
C. 6196K
D. 7200K

Question 436

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as

A. (ΔT)1/4
B. (ΔT)1/2
C. (ΔT)5/4
D. (ΔT)3/4

Question 437

A BTU/hr.ft.2 °F is equal to

A. 1 kcal/hr. m²°C
B. 4.88 kcal/hr. m.2°C
C. 1 kcal/hr. m².°K
D. None of these

Question 438

At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the

A. Buffer zone
B. Turbulent core
C. Both A and B
D. Viscous sub-layer

Question 439

Kg of liquid evaporated per hour in an evaporator is defined as its

A. Capacity
B. Economy
D. None of these

Question 440

In evaporators, lowering the feed temperature

A. Increases the heating area required
B. Reduces the economy
C. Both A and B
D. Decreases the heating area required

Question 441

Grashhoff number is given by

A. gD³.β.Δtρ²/μ²
B. gD2βΔtρ/μ²
C. gD2βΔtP²μ
D. gD³βΔtP²/μ

Question 442

A black body does not __________ radiation.

A. Absorb or emit
B. Refract
C. Reflect
D. Both B & C

Question 443

Boiling point elevation of an ideal solution

A. Increases rapidly with temperature rise
B. Decreases rapidly with temperature rise
C. In independent of pressure
D. Both B and C

Question 444

Radiation heat transfer rates does not depend upon the

A. Type of absorbing surface
B. Distance between the heat source and the object receiving the heat
C. Surface area and temperature of the heat source
D. None of these

Question 445

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

Question 446

Pick out the wrong statement.

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

Question 447

Prandtl number is the ratio of

A. Momentum diffusivity to mass diffusivity
B. Momentum diffusivity to thermal diffusivity
C. Thermal diffusivity to mass diffusivity
D. Thermal diffusivity to momentum diffusivity

Question 448

A multiple effect evaporator as compared to a single effect evaporator of the same capacity has

A. Lower heat transfer area
B. Lower steam economy
C. Higher steam economy
D. Higher solute concentration in the product

Question 449

A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time

A. t = 283 s
B. t = 356 s
C. t = 400 s
D. t = 800 s

Question 450

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

A. Prandtl
B. Reynolds
C. Both A & B
D. Neither A nor B

Question 451

__________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side.

A. Single pass, fixed tube sheet
B. U-tube
C. Three pass, fixed tube sheet
D. None of these

Question 452

In pipe flow, heat is transferred from hot wall to the liquid by

A. Conduction only
B. Forced convection only
C. Forced convection and conduction
D. Free and forced convection

Question 453

Rate of heat flow in conduction.

A. Is directly proportional to temperature gradient
B. Is inversely proportional to temperature gradient
C. Does not depend on temperature gradient
D. Does not depend on temperature gradient & inversely proportional to temperature gradient

Question 454

In a forward feed multiple effect evaporator, the pressure is

A. Highest in last effect
B. Lowest in last effect
C. Same in all effects
D. Dependent on the number of effects

Question 455

Pick out the wrong statement.

A. In case of heat transfer by purely forced convection, GR/Re2 ? 1
B. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as
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

Question 456

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

A. Prandtl number
B. Grashoff number
C. Thermal conductivity
D. Viscosity

Question 457

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

A. Average
B. Geometric mean
C. Product
D. Sum

Question 458

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

Question 459

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

Question 460

In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid

A. Is inversely proportional to the resistance across which the drop occurs
B. And the wall are proportional to individual resistances
C. And the wall is not related
D. None of these

Question 461

If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is

A. 1
B. 2
C. 1-2
D. 4

Question 462

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

Question 463

View factor is important in heat transfer by

A. Steady state conduction
B. Natural convection
C. Forced convection

Question 464

Which is the most suitable for the con-certration of highly concentrated solution?

A. Open pan evaporation
B. Long tube vertical evaporator
C. Agitated film evaporator
D. None of these

Question 465

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

A. Velocity of circulation
B. Liquor-film co-efficient
C. Both A and B
D. Neither A and B

Question 466

The specific heat of the substance is defined as the amount of heat required to raise a unit mass of the substance through a unit rise in temperature.

A. TRUE
B. FALSE

Question 467

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

Question 468

Fourier's law applies to the heat transfer by

A. convection
C. conduction
D. all (a), (b) & (c)

Question 469

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

A. 1 to 100
B. 0.5 to 50
C. 10 to 100
D. 100 to 1000

Question 470

Hot water (0.01 m³ /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.05 m³/min) of density 800 kg/m³ and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately

A. 32
B. 37
C. 45
D. 50

Question 471

When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids?

A. At high fluid velocity
B. At low velocity
C. When fluid flows past a smooth surface
D. None of these

Question 472

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

A. T₁ - T₂
B. T₁ - Ta
C. T₂ - Ta
D. None of these

Question 473

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

Question 474

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

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

Question 475

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

Question 476

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

A. Brinkman number
B. Stanton number
C. Schmidt number
D. Peclet number

Question 477

Circulation pump is located below the evaporater to

A. Avoid cavitation
B. Avoid frequent priming
C. Create more suction head
D. None of these

Question 478

Which of the following has the lowest overall heat transfer co-efficient?

A. Dowtherm
B. Molten sodium
C. Water
D. Air

Question 479

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

A. IR
B. I²R
C. IR²
D. I²R²

Question 480

The unit of conductance in SI unit is

A. W/m
B. W/m²
C. W/°K
D. W/m°K

Question 481

A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions ? Assume that the conductive heat transfer co-efficient is infinitely large.

A. 5 minutes
B. 10 minutes
C. 20 minutes
D. 40 minutes

Question 482

With increase in temperature, the thermal conductivity of steel

A. Increases
B. Decreases
C. Remains unchanged
D. Increases exponentially

Question 483

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

A. Long vertical evaporator
B. Horizontal tube evaporator
C. Agitated film evaporator
D. Calenderia vertical tube evaporator

Question 484

In forced circulation, the heating element is injected

A. Internally
B. Externally
C. Both A and B
D. Neither A nor B

Question 485

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

A. 0.06 to 120
B. 0.6 to 120
C. 1 to 103
D. L to 50

Question 486

1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is

A. 520
B. 200
C. 400
D. 500

Question 487

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m²°C.

A. 10-50
B. 100-500
C. 1000-1500
D. 5000-15000

Question 488

In a cooling tower, water becomes cool by

A. Loosing sensible heat
B. Heat transfer to surroundings
C. Vaporisation due to heat loss to air
D. Loosing latent heat

Question 489

Which of the following is unimportant in forced convection?

A. Reynolds number
B. Prandtl number
C. Grashhoff number
D. None of these

Question 490

The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface)

A. K/h0
B. 2K/h0
C. h0/K
D. h0/2K

Question 491

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the

A. Existence of thermal boundary layer
B. Temperature gradient produced due to density difference
C. Buoyancy of the bubbles produced at active nucleation site
D. None of these

Question 492

What is the geometric mean of two heat transfer areas A₁ and A₂ ?

A. √(A₁ . A₂)
B. √(A₁ + A₂)
C. 1/2 √(A₁ . A₂)
D. 2 √(A₁ . A₂)

Question 493

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

Question 494

What is the absorptivity of a black body?

A. 1
B. 0
C. 0.78
D. 0.95

Question 495

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.

Question 496

Pick out the wrong statement.

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

Question 497

Evaporator tubes are generally

A. Horizontal
B. Vertical
C. Inclined
D. Random

Question 498

An insulator should have

A. Low thermal conductivity
B. High thermal conductivity
C. Less resistance to heat flow
D. A porous structure

Question 499

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

A. Arithmetic
B. Logarithmic
C. Geometric
D. Either A or C

Question 500

In SI units, fouling factor is expressed in

A. m²°K/W
B. W/m²°K
C. m²°K
D. m°K/W

Question 501

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

Question 502

The electromagnetic energy emitted by a perfect radiator corresponding to a temperature T and surface area A is?

A. AσT4Δt, in unit time Δt
B. AeσT4Δt, in unit time Δt
C. Ae4 c) AeσT4
D. AσT4

Question 503

In case of heat transfer by conduction in a hollow cylinder, __________ mean area is used to calculate the heat transfer rate.

A. Geometric
B. Arithmetic
C. Logarithmic
D. Either A, B or C

Question 504

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

A. Linear
B. Hyperbolic
C. Parabolic
D. None of these

Question 505

The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature)

A. (ΔT)²
B. (ΔT)⁴
C. (ΔT)³
D. √(ΔT)

Question 506

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

Question 507

In a shell and tube heat exchanger, square pitch compared to triangular pitch

A. Gives a higher shell side pressure drop
B. Gives a lower shell side pressure drop
C. Can pack more surface area into a shell of given diameter
D. None of these

Question 508

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

A. 1
B. < 1
C. > 1
D. > 5

Question 509

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

Question 510

If we hold a metal rod from one end and dip the other in a source of fire, what will happen to the temperature of the rod at steady state?

A. Be uniform
B. Decrease with time
C. Remain constant at a single value throughout the length of the rod
D. Stay nonuniform

Question 511

Pick out the wrong statement.

A. Heat transfer from a hot body to cold body by the emission of heat waves is called radiation
B. Filmwise condensation takes place on non-wettable surfaces
C. The boiling point of a solution is affected by liquid head as well as boiling point elevation
D. None of these

Question 512

With increase in temperature, the thermal conductivity of a gas

A. Increases
B. Decreases
C. Remains same
D. May increase or decrease depending on the type of gas

Question 513

Three material A, B and C of equal thick-nes and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of __________ °C.

A. 40
B. 95
C. 70
D. 50

Question 514

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

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

Question 515

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

Question 516

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

Question 517

A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m³ and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m².K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is

A. 555
B. 55.5
C. 0.55
D. 0.15

Question 518

Choose the correct equation.

A. Nu = (Re) (Pr) (Gz)
B. Nu = (Re) (Pr) (St)
C. Nu = (Re)(Pr)
D. Nu = (Pr)(St)

Question 519

Pick out the correct statement.

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

Question 520

In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell)

A. 0.25 D
B. 0.75 D
C. 0.50 D
D. None of these

Question 521

The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m². The approximate surface temperature (K) is (Stefan-Boltzman constant = 5.67xl0⁻⁸ W/m².K⁴)

A. 1000
B. 727
C. 800
D. 1200

Question 522

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

A. Re.Gz
B. Nu, Pr
C. Nu, Pr, Re
D. Nu, Gz

Question 523

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

A. Heat transfer co-efficient over the entire heat exchanger is not constant
B. There exists an unsteady state
C. The heat capacity is not constant and there is a phase change
D. None of these

Question 524

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

B. Mechanical strength of the equipment
C. Heat transfer area
D. Heat transfer co-efficient

Question 525

Pick out the wrong statement.

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

Question 526

For specified tube outside diameter, higher BWG means higher

A. Tube thickness
B. Cross-sectional area
C. Weight per unit length
D. None of these

Question 527

1000 Kg of liquid at 30°C in a well stirred vessel has to be heated to 120°C, using immersed coils carrying condensing steam at 150°C. The area of the steam coils is 1.2 m² and the overall heat transfer co-efficient to the liquid is 1500 W/m².°C. Assuming negligible heat loss to the surrounding and specific heat capacity of the liquid to be 4 kJ/kg.°C, the time taken for the liquid to reach desired temperature will be

A. 15 min
B. 22 min
C. 44 min
D. 51 min

Question 528

Which of the following is correct?

A. Rate = Driving force x Resistance
B. Driving force = Rate x Resistance
C. Resistance = Driving force x Rate
D. Rate = Resistance/Driving force

Question 529

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

A. Liquid depth over the heating surface
B. Solution being evaporated
C. Pressure difference between the steam chest and the vapor space above the boiling liquid
D. All of the above

Question 530

In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms⁻². Neglecting the heat capacity of agitator, the temperature of water (in °C) is

A. 40.5
B. 34.4
C. 26.8
D. 25

Question 531

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

A. Antonie
B. Kopp's
C. Lee's
D. Kistyakowski

Question 532

The most conducive surface for dropwise condensation to occur is the __________ surface.

A. Coated
B. Oily
C. Glazed & polished
D. Smooth

Question 533

A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is

A. 6000
B. 24000
C. 60000
D. 48000

Question 534

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

A. Pool
B. Nucleate
C. Transition
D. Film

Question 535

Extremely large or small volumes of fluids are generally best routed through the shell side of a shell and tube heat exchanger, because of the

A. Less corrosion problems
B. Flexibility possible in the baffle arrangement
C. Low pressure drop
D. High heat transfer co-efficient

Question 536

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

A. Viscosity
B. Density
C. Thermal conductivity
D. Heat capacity

Question 537

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. ∞

Question 538

The film co-efficient between condensing vapour and metal wall increases with

A. Increasing temperature of the vapour
B. Decreasing temperature of the vapour
C. Increasing viscosity of the film of condensate
D. Increasing temperature drop

Question 539

The purpose of providing bleed points in the evaporator is to

A. Admit the feed
B. Remove the product
C. Facilitate removal of non-condensable gases
D. Create vacuum

Question 540

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

A. Gases
B. Solids
C. Liquids
D. Both (b) and (c)

Question 541

A 10 cm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m².°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

A. Greater than that for uninsulated steam pipe
B. Less than that of the uninsulated steam pipe
C. Equal to that of the uninsulated steam pipe
D. Less than the steam pipe with 5 cms insulation

Question 542

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

A. Decreases
B. Increases
C. Remains unchanged
D. Increases exponentially

Question 543

200 kg of solids (on dry basis) is subjected to a drying process for a period of 5000 seconds. The drying occurs in the constant rate period with the drying rate as, Nc = 0.5 x 10⁻³ kg/m².s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m²/1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid)

A. 0.5
B. 0.05
C. 0.1
D. 0.15

Question 544

A black body when hot, emits heat radiation of __________ wavelengths.

A. Small
B. Large
C. All
D. One fixed