Heat Transfer

Question 1

Circulation pump is located below the evaporator to
A none of these.
B create more suction head.
C avoid cavitation.
D avoid frequent priming.

Answer 1

B create more suction head.

Question 2

(1) is termed as the __________ number.
A Stanton
B Nusselt
C Prandtl
D Grashoff

Answer 2

C Prandtl

Question 3

Baffle spacing
A should be less than one fifth the diameter of the shell.
B should be less than the inside diameter of the shell.
C is not the same as baffle pitch.
D none of these.

Answer 3

B should be less than the inside diameter of the shell.

Question 4

A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter ‘d’. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to
A d^-1.8
B d^0.8
C d^-1
D d^-0.2

Answer 4

D d^-0.2

Question 5

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

Answer 5

A increases

Question 6

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

Answer 6

D super-saturation

Question 7

Dropwise condensation of steam on cooling surface is promoted
A none of these.
B an oily surface.
C when both the steam and the tube are clean.
D only in presence of air.

Answer 7

B an oily surface.

Question 8

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)^5/4
B (ΔT)^3/4
C (ΔT)^1/4
D ΔT^1/2

Answer 8

B (ΔT)^3/4

Question 9

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 vacuum
B none of these
C high pressure
D backward feed

Answer 9

A vacuum

Question 10

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

Answer 10

C evaporate the water.

Question 11

In a single effect evaporator, the economy is
A none of these
B > 1
C 1
D < 1

Answer 11

D < 1

Question 12

__________ chart is known as transient heat conduction chart.
A Mollier’s
B Heisler’s
C Dirhing’s
D Cox

Answer 12

C Dirhing’s

Question 13

Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by
A keeping the heat transfer surface clean.
B increasing the tube length.
C enhancing the fluid pumping rate.
D none of these.

Answer 13

A keeping the heat transfer surface clean.

Question 14

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 167.5
B 165.4
C 172.5
D 175

Answer 14

165.4

Question 15

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

Answer 15

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

Question 16

The unit of heat transfer co-efficient is
A BTU/hr. °F. ft.
B BTU/hr. ft
C BTU/hr. °F
D BTU/hr. ft^2°F

Answer 16

D BTU/hr. ft^2°F

Question 17

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

Answer 17

B falling film

Question 18

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 18
B 24
C 6
D 12

Answer 18

D 12

Question 19

Multiple effect evaporation is generally recommended, when the
A fuel is cheaply available.
B evaporation on small scale is to be done.
C large scale evaporation of liquor is needed.
D corrosive liquids are to be concentrated.

Answer 19

C large scale evaporation of liquor is needed.

Question 20

The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m^2.K. The fouling factor after one year of operation is found to be hd0 = 2000 W/m^2.K. The overall heat transfer co-efficient at this time is
A 894W/m^2.K
B 1200W/m^2.K
C 333W/m^2.K
D 287 W/m^2.K

Answer 20

C 333W/m^2.K

Question 21

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

Answer 21

C vacuum

Question 22

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

Answer 22

D 85% magnesia cement and glass wool.

Question 23

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 U1 = U2
C U1 = dirt factor - U2
D U2 > U1

Answer 23

B U1 = U2

Question 24

The ratio of momentum diffusivity to thermal diffusivity is the __________ number.
A Nusselt
B Stanton
C Grashoff
D Prandtl

Answer 24

Prandtl

Question 25

LMTD can’t be used as such without a correction factor for the
A all of these
B condensation of mixed vapour in a condenser.
C multipass heat exchanger.
D baffled heat exchanger.

Answer 25

A all of these

Question 26

Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer.
A the least
B no
C lower
D the largest

Answer 26

D the largest

Question 27

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 increase by 2^16
C decrease by 2^2
D remain unchanged

Answer 27

B increase by 2^16

Question 28

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

Answer 28

D saturated

Question 29

In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred
A none of these.
B through a metallic wall.
C by direct contact of hot flue gas with air.
D by heating an intermediate material (like chequor bricks) and then heating the air from this hot material.

Answer 29

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

Question 30

__________ paint has the minimum absorption co-efficient.
A Grey
B Black
C White lead
D Light cream

Answer 30

C White lead

Question 31

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 100
D 10

Answer 31

B 2

Question 32

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

Answer 32

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

Question 33

Baffles are provided in heat exchangers to increase the
A heat transfer co-efficient
B heat transfer area
C heat transfer rate
D fouling factor

Answer 33

A heat transfer co-efficient

Question 34

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is
A none of these.
B uniformly distributed throughout the fluid.
C mainly confined to a thin film of fluid near the surface.
D in the central core of the fluid.

Answer 34

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

Question 35

For a perfectly transparent surface (like gases), the
A reflectivity = 0
B absorptivity = 0
C all of these
D transmissivity = 1

Answer 35

D transmissivity = 1

Question 36

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 horizontal heat exchanger with steam on shell side.
B vertical heat exchanger with steam on shell side.
C horizontal heat exchanger with steam on tube side.
D vertical heat exchanger with steam on tube side.

Answer 36

B vertical heat exchanger with steam on shell side.

Question 37

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

Answer 37

C painting the surface white (with aluminium paint).

Question 38

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 6000
B 5000
C 4000
D 2000

Answer 38

B 5000

Question 39

The heat flux in the nucleate boiling regimes is proportional to (where, ΔT = excess temperature)
A (ΔT)^4
B (ΔT)^3
C √(ΔT)
D (ΔT)^2

Answer 39

B (ΔT)^3

Question 40

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

Answer 40

A infinity.

Question 41

The energy radiated from a surface Q at absolute temperature T is related as
A none of these
B Q ∝ T^2
C Q ∝ T^4
D Q ∝ T^3

Answer 41

A none of these

Question 42

According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction factor)
A 2f
B f/4
C f
D f/2

Answer 42

D f/2

Question 43

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 first increase and then decrease
B increase
C decrease
D first decrease and then increase

Answer 43

A first increase and then decrease

Question 44

Temperature profile in steady state heat transfer is
A parabolic
B hyperbolic
C asymptotic
D linear

Answer 44

D linear

Question 45

With increase in porosity, the thermal conductivity of a solid substance
A decreases
B remains unchanged
C increases
D may increase or decrease; depends on the solid

Answer 45

A decreases

Question 46

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

Answer 46

B Swenson-Walker crystalliser is a batch crystalliser.

Question 47

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 Sphere
B Cube
C All will cool at the same rate
D Plate

Answer 47

A Sphere

Question 48

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 2
B 44928
C 1
D 4

Answer 48

A 2

Question 49

Loss of heat from untagged steam pipe to the ambient air is by
A convection
B all of these
C radiation
D conduction

Answer 49

B all of these

Question 50

In a gas-liquid shell and tube heat exchanger, the
A presence of a non-condensible gas decreases the condensing film co-efficient.
B all of these
C gases under high pressure are routed through the tube side, because high pressure gases are corrosive in nature.
D 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.

Answer 50

B all of these

Question 51

For hot feed, forward feeding as compared to backward feeding results in __________ economy.
A none of these
B no effect on
C decreased
D increased

Answer 51

D increased

Question 52

Grashoff number, which is defined as g . β(Ts - T∞) ρ2. L3/μ2, is proportional to the ratio of buoyancy force to __________ force.
A elastic
B inertial
C none of these
D viscous

Answer 52

D viscous

Question 53

Heat transfer co-efficient (h1) for liquids increases with
A decreasing temperature.
B none of these.
C decreasing Reynolds number.
D increasing temperature.

Answer 53

D increasing temperature.

Question 54

Viscous & heat sensitive liquids are concentrated in __________ evaporators.
A none of these
B agitated film
C open pan
D long tube

Answer 54

B agitated film

Question 55

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 infinity
B zero
C maximum
D minimum

Answer 55

B zero

Question 56

“The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium”. This is __________ law.
A Wien’s displacement
B Planck’s
C Stefan-Boltzman
D Kirchoffs

Answer 56

D Kirchoffs

Question 57

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 43.75
B 35.5
C 48.25
D 81.25

Answer 57

A 43.75

Question 58

The advantage of using a 1 - 2 shell and tube heat exchanger over a 1 - 1 shell and tube heat exchanger is
A higher tube side heat transfer co-efficient.
B higher shell side heat transfer co-efficient.
C lower shell side pressure drop.
D lower tube side pressure drop.

Answer 58

A higher tube side heat transfer co-efficient.

Question 59

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 conduction becomes important
B sub-cooled boiling occurs
C convection becomes important
D radiation becomes important

Answer 59

D radiation becomes important

Question 60

Pick out the correct statement.
A In heat transfer by forced convection, Grashoff number is very important.
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 1 kcal/hr.m.°C is equal to 1 BTU/hr. ft.°F.

Answer 60

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

Question 61

Agitated film evaporator is suitable for concentrating __________ liquids.
A corrosive
B viscous
C foaming
D very thin

Answer 61

B viscous

Question 62

Solid angle subtended by the finite surface at the radiating element is
A called the angle of vision.
B called the view factor.
C proportional to the square of the distance between surfaces.
D expressed in terms of radians.

Answer 62

A called the angle of vision.

Question 63

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))^-0.2
B (D)^-1.8
C (D)^0.2
D (D)^1.8

Answer 63

A (D))^-0.2

Question 64

Which of the following parameters is increased by use of finned tube in a multipass shell and tube heat exchanger ?
A all of these
B Effective tube surface area for convective heat transfer.
C Convective heat transfer co-efficient.
D Tube side pressure drop and the heat transfer rate.

Answer 64

A all of these

Question 65

Prandtl number for most of dry gases is about
A 70
B 0.001
C 0.72
D 150

Answer 65

C 0.72

Question 66

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

Answer 66

D less than that of the uninsulated steam pipe.

Question 67

In a liquid-liquid heat exchanger, for the same process temperature, the ratio of the LMTD in parallel flow to the LMTD in counter flow is always
A > 1
B < 1
C 1
D ∞

Answer 67

B < 1

Question 68

Which of the following has the lowest Prandtl number ?
A Water
B Molten sodium (a coolant used in fast breeder reactor)
C Transformer oil
D Dilute H2SO4

Answer 68

B Molten sodium (a coolant used in fast breeder reactor)

Question 69

Heat flux, as defined in heat flow is analogous to __________ in electricity flow.
A none of these
B voltage
C resistance
D current

Answer 69

D current

Question 70

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 straight line
B parabola
C circular arc
D ellipse

Answer 70

A straight line

Question 71

Thermal diffusivity of a material
A all of these
B is defined as K/ρ . Cp.
C has the unit m^2 /sec.
D is the ratio of thermal conductivity to thermal capacity.

Answer 71

A all of these

Question 72

Electromagnetic radiations propagate in vacuum with a velocity of __________ metre/second.
A 3 x l0^5
B 3 x l0^12
C 3 x l0^8
D 3 x l0^10

Answer 72

C 3 x l0^8

Question 73

In a boiling curve, the peak heat flux is called the __________ point.
A Nusselt
B boiling
C Leidenfrost
D burnout

Answer 73

D burnout

Question 74

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)1/4
B (ΔT)3/2
C (ΔT)2
D √ΔT

Answer 74

A (ΔT)1/4

Question 75

Heat transfer occurs by natural convection because change in temperature causes difference in
A density
B heat capacity
C thermal conductivity
D viscosity

Answer 75

A density

Question 76

With increase in temperature, the thermal conductivity of most liquids
A remains same
B decreases
C first increases upto a certain temperature and then becomes constant
D increases

Answer 76

B decreases

Question 77

LMTD for counterflow and prallel flow heat exchanger will be the same, when the
A outlet temperature of both the hot and cold fluid are same.
B none of these.
C cold fluid is heated to a certain temperature by condensing steam (isothermal fluid).
D outlet temperature of hot fluid is less than the outlet temperature of the cold fluid.

Answer 77

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

Question 78

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m^2°C.
A 100-500
B 1000-1500
C 5000-15000
D 18537

Answer 78

C 5000-15000

Question 79

With increase in the distance between the heat source and the object receiving the heat, the radiation heat transfer
A increases exponentially
B decreases
C remains unaffected
D increases

Answer 79

B decreases

Question 80

The thickness of condensate layer in filmwise condensation depends on the
A liquid flow rate from the surface
B all of these
C condensation rate
D surface configuration

Answer 80

B all of these

Question 81

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 (R1/R2)2
B 0
C R2/(R1+R2)
D 1

Answer 81

C R2/(R1+R2)

Question 82

The separation of liquid droplets from the vapor is done by a/an __________ , in the evaporators.
A steam ejector
B vacuum pump
C compressor
D entrainment separator

Answer 82

D entrainment separator

Question 83

With the increase of temperature, the Col-burn jH factor
A may increase or decrease ; depending on temperature.
B increases.
C decreases.
D remains unchanged.

Answer 83

B increases.

Question 84

Minimum recommended baffle spacing in a shell and tube heat exchanger is about (where, D = shell diameter)
A 0.66 D
B 0.2 D
C 0.80 D
D 0.5 D

Answer 84

B 0.2 D

Question 85

The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns.
A 100-1000
B 18384
C 0.38-0.78
D 0.5-50

Answer 85

D 0.5-50

Question 86

When vaporisation takes place directly at the heating surface, it is called
A none of these
B vapour binding
C nucleate boiling
D film boiling

Answer 86

C nucleate boiling

Question 87

For heat flow through very thick walled cylinder, use____mean radius.
A either arithmetic or geometric
B arithmetic
C logarithmic
D geometric

Answer 87

C logarithmic

Question 88

Which of the following situations can be approximated to a steady state heat transfer system ?
A A sub-cooled refrigerant liquid at 8°C flowing at the rate of 6 Kg/minute through a copper pipe exposed to atmospheric air at 35°C.
B 10 kg of dry saturated steam at 8 kgf/cm^2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C.
C A red hot steel slab (having outside surface temperature as 1300°C) exposed to the atmosheric air at 35°C.
D Boiling brine kept in open vessel when the bottom surface temperature of the vessel is maintained constant at 180°C.

Answer 88

B 10 kg of dry saturated steam at 8 kgf/cm^2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35°C.

Question 89

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

Answer 89

C decreases

Question 90

Film boiling is usually not desired in commercial equipments, because
A none of these.
B it is not economic.
C the heat transfer rate is low in view of the large temperature drop.
D it is difficult to maintain.

Answer 90

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

Question 91

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

Answer 91

A equal to

Question 92

Which of the following has the minimum thermal conductivity ?
A Tar
B Steel
C Nitrogen
D Carbon black

Answer 92

C Nitrogen

Question 93

The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is
A more
B some
C either more or less ; depends on the nature of vapor
D less

Answer 93

D less

Question 94

The advantage of backward feed multiple effect evaporators over forward feed units is that
A equal heat transfer co-efficients exist in various effects.
B there is no additional cost of pumping.
C heat sensitive material can be handled.
D most concentrated liquid is at highest temperature.

Answer 94

D most concentrated liquid is at highest temperature.

Question 95

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

Answer 95

B logarithmic

Question 96

Prandtl number is the reciprocal of
A Thermal diffusivity/Momentum diffusivty
B thermal diffusivity x Momentum
C Thermal diffusivity x Mass diffusivity
D Mass diffusivity x Momentum diffusivity

Answer 96

A Thermal diffusivity/Momentum diffusivity

Question 97

What is the absorptivity of a black body ?
A 1
B 0.95
C 0.78
D 0

Answer 97

A 1

Question 98

The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is
A 2
B 4
C 44930
D 44928

Answer 98

C 44930

Question 99

Prandtl number is the ratio of
A momentum diffusivity to thermal diffusivity.
B mass diffusivity to thermal diffusivity.
C thermal diffusivity to mass diffusivity.
D thermal diffusivity to momentum diffusivity.

Answer 99

A momentum diffusivity to thermal diffusivity.

Question 100

Boiling point of a solution according to Duhring’s rule is a linear function of the __________ of water.
A viscosity
B thermal conductivity
C density
D boiling point (at the same pressure)

Answer 100

D boiling point (at the same pressure)

Question 101

(1) is called the __________ number
A Peclet
B Stanton
C none of these
D Graetz

Answer 101

D Graetz

Question 102

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 local
B pool
C nucleate
D saturated

Answer 102

A local

Question 103

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

Answer 103

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

Question 104

The Fourier number (defined as a.t/L^2) is used in the analysis of problem involving heat transfer by
A transient conduction
B steady state conduction
C forced convection
D natural convection

Answer 104

A transient conduction

Question 105

As the difference between the wall temperature and bulk temperature increases, the boiling heat transfer co-efficient
A goes through a minimum.
B continues to decrease.
C goes through a maximum.
D continues to increase.

Answer 105

A goes through a minimum.

Question 106

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

Answer 106

D Grashoff

Question 107

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

Answer 107

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

Question 108

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 forced convection
C entry length problem in laminar forced conduction (developing thermal boundary layer)
D mixed convection (both free and forced)

Answer 108

D mixed convection (both free and forced)

Question 109

Evaporator tubes are generally
A horizontal
B inclined
C random
D vertical

Answer 109

D vertical

Question 110

Out of the following four assumptions used in the derivation of the equation for (1) LMTD , which one is subject to the largest deviation in practice ?
A No partial phase change in the system.
B Constant overall heat transfer co-efficient.
C Constant specific heat.
D Constant rate of fluid flow.

Answer 110

D Constant rate of fluid flow.

Question 111

In case of evaporators, liquid entrainment results primarily due to
A high evaporation rate.
B high heat transfer rate.
C foaming of the solution.
D high vacuum in the evaporator.

Answer 111

C foaming of the solution.

Question 112

Heat transfer by radiation between two bodies at T1 & T2 and in an ambient temperature of Ta°C depends on
A T1 - T2
B T2 - Ta
C T1 - Ta
D none of these

Answer 112

D none of these

Question 113

Choose the correct equation.
A Nu = (Pr)(St)
B Nu = (Re) (Pr) (Gz)
C Nu = (Re) (Pr) (St)
D Nu = (Re)(Pr)

Answer 113

C Nu = (Re) (Pr) (St)

Question 114

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

Answer 114

B accounts for additional resistances to heat flow.

Question 115

Tube pitch is the __________ of tube diameters and the clearances.
A none of these
B difference
C ratio
D sum

Answer 115

D sum

Question 116

Multipass heat exchangers are used
A because of simplicity of fabrication.
B to obtain higher heat transfer co-efficient and shorter tube.
C for low heat load.
D to reduce the pressure drop.

Answer 116

B to obtain higher heat transfer co-efficient and shorter tube.

Question 117

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 E/C
B C/E
C
D CE

Answer 117

B C/E

Question 118

Steam is routed through the tube in case of a __________ evaporator.
A short tube vertical
B basket type
C horizontal tube
D long tube vertical

Answer 118

C horizontal tube

Question 119

The equation, Nst = f/2, is the __________ analogy.
A Colburn
B Prandtl
C none of these
D Reynolds

Answer 119

D Reynolds

Question 120

Pick out the wrong statement.
A The equivalent diameter of heat transfer for a duct of square cross-section (having each side as ‘x’) is equal to 4x.
B The effectiveness of nucleate boiling depends basically on the ease with which the bubbles are formed and detached from the heating surface.
C Distillation process is not the same as evaporation.
D In case of heat transfer by purely forced convection, GR/Re2 ≤ 1.

Answer 120

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

Question 121

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

Answer 121

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

Question 122

The actual temperature drop across the heating surface in an evaporator depends on the
A feed.
B pressure difference between steam chest and vapour space.
C all of these
D depth of liquid over heating surface.

Answer 122

C all of these

Question 123

When warm and cold liquids are mixed, the heat transfer is mainly by
A convection
B both(a) & (c)
C radiation
D conduction

Answer 123

A convection

Question 124

Prandtl and Reynolds analogy are same, when Prandtl number is
A 1
B 0.5
C 1.5
D > 2

Answer 124

A 1

Question 125

Among liquids, water has a comparatively high value of thermal conductivity, due to its
A low density
B dense structure
C partial ionisation
D high viscosity

Answer 125

C partial ionisation

Question 126

Heat transfer by __________ may not necessarily require the presence of a medium.
A radiation
B natural convection
C forced convection
D conduction

Answer 126

A radiation

Question 127

Use of transverse baffles in a shell and tube heat exchanger is done to increase the
A turbulence of shell side fluid.
B all of these
C flow velocity.
D rate of heat transfer.

Answer 127

B all of these

Question 128

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 √Δt
C Δt^3
D Δt^2

Answer 128

A Δt

Question 129

Which of the following has the highest thermal conductivity ?
A Silver
B Water
C Brick
D Air

Answer 129

A Silver

Question 130

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 9000
B 3000
C 4000
D 4600

Answer 130

C 4000

Question 131

For what value of Prandtl number, the Col-burn analogy is valid ?
A 1 to 103
B l to 50
C 0.6 to 120
D 0.06 to 120

Answer 131

C 0.6 to 120

Question 132

Which of the following has maximum thermal conductivity ?
A Iron
B Tar
C Nitrogen
D Coal

Answer 132

A Iron

Question 133

Fourier’s law applies to the heat transfer by
A all of these
B convection
C radiation
D conduction

Answer 133

D conduction

Question 134

Which characteristic of a fluid is not important in deciding its route in a shell and tube heat exchanger ?
A None of these
B Viscosity
C Corrosiveness
D Fouling characteristic

Answer 134

A None of these

Question 135

Heat flux through several resistances in series in analogous to the current flowing through several
A none of these.
B resistances in parallel.
C capacitors in series.
D resistances in series.

Answer 135

D resistances in series.

Question 137

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 14.6 kW/m^2
B 11.2 kW/m^2
C 16.5 kW/m^2
D 12.0 kW/m^2

Answer 137

C 16.5 kW/m^2

Question 138

Steam traps are provided in steam carrying pipelines to
A release excess steam pressure by bleeding steam.
B none of these.
C remove condensate and inert gases.
D condense steam.

Answer 138

C remove condensate and inert gases.

Question 139

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 400
B 520
C 200
D 500

Answer 139

A 400

Question 140

Absorptivity and refletivity of a perfect black body are respectively
A 0 and 0.5
B 1 and 0
C 1 and ∞
D 0 and 1

Answer 140

B 1 and 0

Question 141

Dietus-Boelter equation used for the determination of heat transfer co-efficient is valid
A for liquid metals.
B when Grashhoff number is very important.
C for fluids in laminar flow.
D for fluids in tubulent flow.

Answer 141

D for fluids in tubulent flow.

Question 142

It is not preferable to use superheated steam in evaporators, because of its very
A low film co-efficient
B none of these
C high temperature
D high pressure

Answer 142

A low film co-efficient

Question 143

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 excessive corrosion
B its evaporation loss
C decrease in heat exchanger efficiency
D uneconomic LMTD

Answer 143

A excessive corrosion

Question 144

A 2-4 heat exchanger involves
A only counter-flow of fluids.
B smaller pressure drop compared to 1-2 exchanger.
C both counter and parallel-flow of the fluids.
D only parallel-flow of fluids.

Answer 144

C both counter and parallel-flow of the fluids.

Question 145

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

Answer 145

C Wien’s

Question 146

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

Answer 146

D account for the uneven expansion of shell and tube bundles.

Question 147

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

Answer 147

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

Question 148

Prandtl number is the ratio of
A thermal diffusivity to mass diffusivity.
B thermal diffusivity to momentum diffusivity.
C momentum diffusivity to mass diffusivity.
D momentum diffusivity to thermal diffusivity.

Answer 148

D momentum diffusivity to thermal diffusivity.

Question 149

Black liquor generated during paper manufacture is concentrated in a
A multiple effect evaporators followed by a crystalliser.
B multiple effect evaporator.
C single effect evaporator.
D single effect evaporator followed by a crystalliser.

Answer 149

B multiple effect evaporator.

Question 150

Maximum heat transfer rate is obtained in __________ flow.
A turbulent
B creeping
C transition region
D laminar

Answer 150

A turbulent

Question 151

For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it
A is easy to operate and maintain.
B is more economical.
C all of these
D occupies smaller space.

Answer 151

C all of these

Question 152

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

Answer 152

C tube diameter

Question 153

At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below : (1) The thermal conductivity of material I
A is smaller than that of II.
B is greater than that of II.
C can be greater than or smaller than that of II.
D is equal to that of II.

Answer 153

A is smaller than that of II.

Question 154

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 kA < 0.5kB
B kA>2 kB
C CPA > CPB
D CPA < CPB

Answer 154

A kA < 0.5kB

Question 155

The number of kg vaporised per kg of steam fed to the evaporator is defined as
A rate of evaporation
B rate of vaporisation
C economy
D capacity

Answer 155

C economy

Question 156

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

Answer 156

C 1-1 heat exchanger

Question 157

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

Answer 157

D that across the entire pipe

Question 158

Multiple effect evaporators ar used to
A increase the steam economy & the capacity.
B increase the steam economy & decrease the capacity.
C decrease the steam economy & the capacity.
D decrease the steam economy & increase the capacity.

Answer 158

A increase the steam economy & the capacity.

Question 159

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

Answer 159

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

Question 160

Double pipe heat exchangers are preferably useful, when
A overall heat transfer co-efficient is very high.
B a corrosive liquid is to be heated.
C high viscosity liquid is to be cooled.
D requirement of heat transfer area is low.

Answer 160

D requirement of heat transfer area is low.

Question 161

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

Answer 161

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

Question 162

In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side __________ the heat transfer rate.
A does not affect
B decreases
C increases
D may increase or decrease, depends on the type of baffle

Answer 162

C increases

Question 163

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP)R and the co-efficient of performance as a heat pump (COP)HP are
A (COP)R = (COP)HP = 2.5
B (COP)R = 1.5; (COP)HP = 2.5
C (COP)R = (COP)HP = 0.6
D (COP)R = 2.5; (COP)HP = 1.5

Answer 163

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

Question 164

Which type of heat exchanger is preferred for heavy heat loads ?
A Double pipe
B None of these
C Plate fine
D Series and parallel set of shell and tube

Answer 164

D Series and parallel set of shell and tube

Question 165

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 = 5hL
C ha = 2hL
D ha = hL

Answer 165

C ha = 2hL

Question 166

In case of heat flow by conduction for a cylindrical body with an internal heat source, the nature of temperature distribution is
A hyperbolic
B none of these
C parabolic
D linear

Answer 166

C parabolic

Question 167

Vent pipes are provided in a condenser to
A purge the condenser.
B remove non-condensable gases.
C facilitate easy cleaning of tubes.
D none of these.

Answer 167

B remove non-condensable gases.

Question 168

If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.
A increase
B not affect
C increase the condensing film co-efficient as well as
D decrease

Answer 168

D decrease

Question 169

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 parallel flow with process stream on shell side.
B parallel flow with process stream on tube side.
C counter flow with process stream on shell side.
D counter flow with process stream on tube side.

Answer 169

C counter flow with process stream on shell side.

Question 170

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 chemical potentials
B activity co-efficients
C mass transfer co-efficients
D concentrations

Answer 170

D concentrations

Question 171

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

Answer 171

C 1

Question 172

Which of the following is unimportant in forced convection ?
A none of these
B Prandtl number
C Reynolds number
D Grashhoff number

Answer 172

D Grashhoff number

Question 173

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

Answer 173

C basket type

Question 174

Which of the following has the lowest overall heat transfer co-efficient ?
A Dowtherm
B Air
C Water
D Molten sodium

Answer 174

B Air

Question 175

For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and pressure drop are
A linearly related
B never different
C same
D different

Answer 175

D different

Question 176

Which of the following is directly concerned with the heat transfer ?
A Euler number
B Sherwood number
C Grashoff number
D Strouhal number

Answer 176

C Grashoff number

Question 177

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 Reynolds number for the flow involved is < 2100.
C n = 0.3 is used for cooling.
D Reynolds number for the flow involved is > 10000.

Answer 177

B Reynolds number for the flow involved is < 2100.

Question 178

In case of a supercooled solution, which is on the verge of crystallisation, the free energy of the solution as compared to that of the solid is
A more or less; depends on the nature of solution
B same
C more
D less

Answer 178

C more

Question 179

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

Answer 179

B high

Question 180

In a backward feed multiple effect evaporator
A feed is introduced in the first effect.
B none of these.
C no pumps are required between successive effects.
D feed flows from low pressure to high pressure.

Answer 180

D feed flows from low pressure to high pressure.

Question 181

Baffles in the shell side of a shell and tube heat exchanger
A force the liquid to flow parallel to the bank.
B increase the shell side heat transfer co-efficient.
C increase the cross-section of the shell side liquid.
D decrease the shell side heat transfer co-efficient.

Answer 181

B increase the shell side heat transfer co-efficient.

Question 182

With increase in temperature, the thermal conductivity of steel
A increases
B increases exponentially
C decreases
D remains unchanged

Answer 182

C decreases

Question 183

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 cylinder
B equal for all the three
C sphere
D cube

Answer 183

D cube

Question 184

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

Answer 184

C capacity

Question 185

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 none of these
D 1

Answer 185

D 1

Question 186

Trap is used to remove __________ from steam pipe lines.
A non-condensables
B condensate
C none of these
D steam

Answer 186

B condensate

Question 187

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m^2 .°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the
A lower pressure drop through the exchanger is desired.
B temperature of the incoming vapor is very high.
C condensate is corrosive in nature.
D higher condensing film co-efficient is desired.

Answer 187

C condensate is corrosive in nature.

Question 188

In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to __________ the velocity head.
A four times
B square of
C square root of
D twice

Answer 188

A four times

Question 189

Thermal conductivities of most of the liquids __________ with rise in temperature.
A increases
B remains unchanged
C decreases
D may increase or decrease; depends on the liquid

Answer 189

C decreases

Question 190

An insulator should have
A less resistance to heat flow.
B low thermal conductivity.
C a porous structure.
D high thermal conductivity.

Answer 190

B low thermal conductivity.

Question 191

The purpose of floating head in a heat exchanger is to
A decrease the pressure drop.
B provide support for tubes.
C avoid buckling of tubes.
D facilitate its lengthening, if needed.

Answer 191

C avoid buckling of tubes.

Question 192

Which of the following is concerned with both heat and mass transfer ?
A Froude number
B Kutateladze number
C Lewis relationship
D Nusselt number

Answer 192

C Lewis relationship

Question 193

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

Answer 193

C 1

Question 194

When vaporisation takes place through a blanketting film of gas, the phenomenon is termed as __________ boiling.
A pool
B film
C nucleate
D transition

Answer 194

B film

Question 195

Heat transfer by natural convection is enhanced in system with
A low temperature gradients.
B high viscosity.
C high co-efficient of thermal expansion.
D low density change with temperature.

Answer 195

C high co-efficient of thermal expansion.

Question 196

Radiation energy is emitted by all the substances, which are above
A room temperature
B 0°C
C 100°C
D 0°K

Answer 196

D 0°K

Question 197

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 0.45
B 0.35
C 0.85
D 0.55

Answer 197

A 0.45

Question 198

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

Answer 198

A results in making part of the heating surface inactive.

Question 199

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 0.7
D 0.6

Answer 199

C 0.7

Question 200

In a multiple effect evaporator, the effect of boiling point elevation is to
A none of these
B increase the economy
C reduce the capacity
D reduce the economy

Answer 200

C reduce the capacity

Question 201

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

Answer 201

A > 1

Question 202

For flow over a flat plate, the ratio of thermal boundary layer thickness, ‘xt’ and hydrodynamic boundary layer thickness ‘x’ is equal to (where, NPr = Prandtl number)
A NPr
B NPr^1/3
C NPr^-1
D NPr^-1/3

Answer 202

B NPr^1/3

Question 203

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

Answer 203

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

Question 204

Fouling factor’ used in the design of a multipass shell and tube heat exchanger is a
A none of these.
B conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient.
C non-dimensional factor.
D factor of safety.

Answer 204

D factor of safety.

Question 205

A BTU/hr.ft.2 °F is equal to
A 4.88 kcal/hr. m.^2°C.
B 1 kcal/hr. m^2.°K.
C none of these.
D 1 kcal/hr. m2°C.

Answer 205

A 4.88 kcal/hr. m.^2°C.

Question 206

The value of Stefan-Boltazman constant in SI unit is
A 0.1714 x 1^0-8W/m^2.°K^4
B 5.6697 x 1^0-8W/m^2.°K^4
C 0.1714 x 1^0-8kcal/m^2. °K^4
D 5.6697 x 1^0-8kcal/m^2 . °K^4

Answer 206

B 5.6697 x 1^0-8W/m^2.°K^4

Question 207

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

Answer 207

D decrease

Question 208

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

Answer 208

B turbulent

Question 209

In the equation Q = UAΔt; Δt is
A logarithmic mean temperature difference.
B the difference of average bulk temperatures of hot and cold fluids.
C arithmetic mean temperature difference.
D geometric mean temperature difference.

Answer 209

A logarithmic mean temperature difference.

Question 210

Air is best heated with steam in a heat exchanger of
A double pipe type with fin on steam side.
B shell and tube type.
C double pipe type with fin on air side.
D plate type.

Answer 210

C double pipe type with fin on air side.

Question 211

Which area is used in case of heat flow by conduction through a cylinder ?
A None of these
B Arithmetic mean area
C Logarithmic mean area
D Geometric mean area

Answer 211

C Logarithmic mean area

Question 212

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

Answer 212

A t = 800 s

Question 213

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

Answer 213

D oily

Question 214

Grashhoff number is given by
A gD^3.β.Δtρ^2/μ^2
B gD^2βΔtρ/μ^2
C gD^3βΔtP^2/μ D gD^2βΔtP^2μ

Answer 214

A gD^3.β.Δtρ^2/μ^2

Question 215

A hot body will radiate heat most rapidly, if its surface is
A black & polished
B white & rough
C white & polished
D black & rough

Answer 215

D black & rough

Question 216

The ratio of kinematic viscosity to thermal diffusivity is called the __________ number.
A Stanton
B Peclet
C Nusselt
D Prandtl

Answer 216

D Prandtl

Question 217

Increasing the liquor level in the evaporator results in the
A increase in liquor film co-efficient.
B increased true temperature drop.
C decreased effect of hydrostatic head.
D decreased capacity.

Answer 217

D decreased capacity.

Question 218

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

Answer 218

A always between h1 and h2

Question 219

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/4 and 2 D
C D and 2 D
D D/2 and 2 D

Answer 219

A D/5 and D

Question 220

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

Answer 220

C both the tube sheets fixed.

Question 221

If heat transfer rate varies with the time, it is termed as
A steady state conduction
B forced convection
C none of these
D monochromatic radiation

Answer 221

C none of these

Question 222

Multiple effect evaporation accounts for
A steam economy
B none of these
C lower operating costs
D investment economy

Answer 222

A steam economy

Question 223

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 25
D 26.8

Answer 223

B 34.4

Question 224

Convective heat transfer, in which heat is transferred by movement of warmed matter is described by
A none of these
B Fourier’s law
C Fick’s law
D Newton’s law of cooling

Answer 224

D Newton’s law of cooling

Question 225

In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to (where, D = inside diameter of shell)
A none of these
B 0.75 D
C 0.50 D
D 0.25 D

Answer 225

B 0.75 D

Question 226

The Dietus-Boelter equation for convective leat transfer (1) cannot be used for
A molten metals
B very low Grashoff number
C low Reynold’s number
D all of these

Answer 226

D all of these

Question 227

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 6.12 x 10^5
B 7.24 x 10^5
C 9.08 x 10^5
D 3.06 x l0^5

Answer 227

D 3.06 x l0^5

Question 228

In case of __________ boiling, the bubbles formed on a submerged hot surface get absorbed in the mass of the liquid.
A pool
B none of these
C low pressure
D nucleate

Answer 228

A pool

Question 229

With increase in temperature, the thermal conductivity of non-metallic amorphous solids
A decreases
B remains constant
C first decreases upto certain temperature and then increases
D increases

Answer 229

D increases

Question 230

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

Answer 230

A highly viscous

Question 231

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

Answer 231

D remove water resulting from partial condensation of steam.

Question 232

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is
A 4.36
B 2.36
C dependent on NRe only
D 120.36

Answer 232

A 4.36

Question 233

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

Answer 233

D film

Question 234

Which is the most suitable for cold viscous feed?
A Forward feed
B Mixed feed
C Backward feed
D Parallel feed

Answer 234

C Backward feed

Question 235

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 polished bodies only
B a black body
C black painted bodies only
D all bodies

Answer 235

D all bodies

Question 236

Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by (1) This is valid for the value of NRe equal to
A > 4000
B 2100-4000
C > 10000
D < 2100

Answer 236

C > 10000

Question 237

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 2^0.4
B 4^0.4
C 2^0.8
D 4^0.8

Answer 237

D 4^0.8

Question 238

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 thrice
B four times
C once
D twice

Answer 238

D twice

Question 239

Multiple effect evaporators are commonly used in the manufacture of
P. Paper Q. Superphosphate R. Sugar S. Fats
A P and S
B R and S
C P and Q
D P and R

Answer 239

A P and S

Question 240

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

Answer 240

A Double pipe

Question 241

Which of the following is the most controlling factor for the rate of bubble detachment from the hot solid surface ?
A Interfacial tension
B Liquid viscosity
C Liquid density
D Hot surface temperature

Answer 241

A Interfacial tension

Question 242

For specified tube outside diameter, higher BWG means higher
A tube thickness
B none of these
C weight per unit length
D cross-sectional area

Answer 242

D cross-sectional area

Question 243

Heat exchanger tubes are never made of
A lead
B plain carbon steel
C copper
D stainless steel

Answer 243

A lead

Question 244

Which has the lowest Prandtl number ?
A Water
B Lube oil
C Aqueous solution
D Liquid metal

Answer 244

D Liquid metal

Question 245

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

Answer 245

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

Question 246

Choose the most important factor on which the heat conducted through a wall in a unit time will depend on ?
A Temperature difference between the two surfaces of the wall.
B Material of the wall.
C Thickness of the wall.
D Area of the wall perpendicular to heat flow.

Answer 246

A Temperature difference between the two surfaces of the wall.

Question 247

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 opreate at atmospheric pressure.
C none of these.
D evaporators operate under vacuum.

Answer 247

A solution has an elevation of boiling point.

Question 248

The equation, (NSt x N^2/3Pr) = f/2, is the __________ analogy.
A Colburn
B none of these.
C Reynolds
D Prandtl

Answer 248

A Colburn

Question 249

The statement that “maximum wavelength of radiation is inversly proportional to the temperature” is __________ law.
A none of these
B Planck’s
C Wien’s displacement
D Stefan-Boltzman’s

Answer 249

C Wien’s displacement

Question 250

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

Answer 250

B increasing temperature of the vapour.

Question 251

Overall thermal resistance for conductive heat transfer through a series of flat resistances is equal to the
A sum of all resistances.
B average of all resistances.
C maximum resistance in the series.
D minimum resistance presents in the series.

Answer 251

A sum of all resistances.

Question 252

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

Answer 252

A Triangular pitch

Question 253

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

Answer 253

B both(a) & (b)

Question 254

Indirect contact heat exchangers are preferred over direct contact heat exchangers, because
A there is no mist formation.
B heat transfer co-efficient are high.
C there is no risk of contamination.
D cost of equipment is lower.

Answer 254

C there is no risk of contamination.

Question 255

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

Answer 255

A and the wall are proportional to individual resistances.

Question 256

Prandtl and Reynold’s analogies are identical for Prandtl number value of
A 1
B 5
C 0.5
D 0

Answer 256

A 1

Question 257

A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun ?
A Grey paint
B White paint
C Yellow paint
D Black paint

Answer 257

D Black paint

Question 258

Evaporation of 1kg of water from a solution in a single effect evaporator requires about __________ kg of steam.
A 0.4 - 0.6
B 1-1.3
C 1.8-2
D 2 - 2.4

Answer 258

B 1-1.3

Question 259

Which of the following accessories is provided in the vapor line of an evaporator for removing the entrained liquid ?
A Catchall
B Vent
C Bleed point
D Baffle

Answer 259

A Catchall

Question 260

For an ideal black body
A absorptivity = 1
B reflectivity = 1
C transmissivity = 1
D emissivity = 0

Answer 260

A absorptivity = 1

Question 261

What is the emissivity of a black body ?
A 0
B 0.5
C 0.9
D 1

Answer 261

D 1

Question 262

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

Answer 262

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

Question 263

jH factor for heat transfer depends upon the __________ number.
A Biot
B Nusselt
C Prandtl
D Reynolds

Answer 263

D Reynolds

Question 264

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 or decreases depending on number of shell passes.
C decreases.
D increases.

Answer 264

C decreases.

Question 265

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 viscosity
C density
D pressure

Answer 265

C density

Question 266

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

Answer 266

A none of these

Question 267

In forced convection, the heat transfer depends on
A Re only
B Re, Pr
C mainly Gr
D Re, Gr

Answer 267

B Re, Pr

Question 268

What is the thermal conductivity of a perfect heat insulator ?
A ∞
B zero
C between 0 and ∞
D one

Answer 268

B zero

Question 269

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 727
B 1000
C 800
D 1200

Answer 269

B 1000

Question 270

Crystallisation of solids from a homogeneous solution is a/an __________ process.
A highly endothermic
B mildly endothermic
C none of these
D exothermic

Answer 270

D exothermic

Question 271

Crystal size in a continuous crystalliser depends upon the
A degree of turbulence.
B rate of heat transfer.
C all of these
D degree of supersaturation.

Answer 271

C all of these

Question 272

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 37
B 6.1
C 1
D 1.74

Answer 272

B 6.1

Question 273

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

Answer 273

D finned tube heat exchanger with air outside and steam inside.

Question 274

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 same in either ‘a’, b’ or ‘c’
B counterflow
C parallel
D mixed

Answer 274

A same in either ‘a’, b’ or ‘c’

Question 275

Log mean temperature difference (LMTD) cannot be used, if
A none of these.
B there exists an unsteady state.
C heat transfer co-efficient over the entire heat exchanger is not constant.
D the heat capacity is not constant and there is a phase change.

Answer 275

A none of these.

Question 276

The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is
A Schmidt number.
B Stanton number.
C Sherwood number.
D Nusselt number.

Answer 276

A Schmidt number.

Question 277

Value of Prandtl number for water ranges from
A l to 2
B 100 to 500
C 5 to 10
D 1000 to 2000

Answer 277

C 5 to 10

Question 278

Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity ?
A iron plate
B aluminium foil
C refractory bricks
D coke breeze

Answer 278

D coke breeze

Question 279

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

Answer 279

A increases the overall heat transfer coefficient.

Question 280

The film thickness for laminar film condensation on vertical surface __________ from top to bottom.
A cummulatively increases
B and the surface conductance increase
C remains constant
D cummulatively decreases

Answer 280

A cummulatively increases

Question 281

__________ equation relates the thermal conductivity of a solid to its temperature.
A Kopp’s
B Antonie
C Lee’s
D Kistyakowski

Answer 281

C Lee’s

Question 282

Stefen’s block body radiation law can also be derived from __________ law.
A Kirchoffs
B Fourier’s
C none of these
D Planck’s

Answer 282

D Planck’s

Question 283

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 44 min
B 51 min
C 15 min
D 22 min

Answer 283

B 51 min

Question 284

The critical radius of insulation for cylindrical pipe is (where, hi = heat transfer coefficient at inside of the pipe )
A hi/K
B 2K/h0
C 2hi/K
D K/h0

Answer 284

D K/h0

Question 285

The absorptivity of a body is equal to its emissivity
A for circular bodies.
B at a particular temperature.
C under thermal equilibrium.
D none of these.

Answer 285

C under thermal equilibrium.

Question 286

The rate of emission of radiation by a body does not depend upon the
A shape and porosity of the body.
B surface temperature of the body.
C nature of the surface.
D wavelength of radiation.

Answer 286

A shape and porosity of the body.

Question 287

The critical radius ‘r’ of insulation on a pipe is given by
A r = k/h
B r = k/2h
C r = h/k
D r = 2k/h

Answer 287

A r = k/h

Question 288

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

Answer 288

B < 1

Question 289

Presence of a non-condensing gas in a condensing vapour
A is desirable to increase the film co-efficient.
B none of these.
C decreases thermal resistance.
D increases the rate of condensation.

Answer 289

B none of these.

Question 290

Which of the following is not concerned with the heat transfer?
A Stanton number
B Peclet number
C Brinkman number
D Schmidt number

Answer 290

D Schmidt number

Question 291

The steam ejector is used to
A superheat the steam.
B remove condensate from the steam pipelines.
C none of these.
D create vacuum.

Answer 291

D create vacuum.

Question 292

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 48000
C 60000
D 24000

Answer 292

24000

Question 293

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

Answer 293

D 0

Question 294

Which of the following has maximum thermal conductivity at the same temperature?
A Steel
B All have the same conductivity
C Air
D Petrol

Answer 294

A Steel

Question 295

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 2K/h0
B h0/2K
C K/h0
D h0/K

Answer 295

A 2K/h0

Question 296

The units of resistance to heat transfer is
A W.m^-2.K^-1
B J.m^-2.K^-1
C J.m^-1.K^-1
D W^-1m^2K

Answer 296

D W^-1m^2K

Question 297

Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low
A hardness
B suspended solids content
C all of these
D dissolved soilds content

Answer 297

C all of these

Question 298

In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
A less than 45°C
B equal to 45°C
C more than 45°C
D initially decreases and remains constant thereafter.

Answer 298

C more than 45°C

Question 299

h.D/K is called the __________ number.
A Peclet
B Grashoff
C Nusselt
D Rayleigh

Answer 299

C Nusselt

Question 300

A body is called grey if the monochromatic emissivity of the body is
A unity
B different for all wavelengths
C same for all wavelengths
D zero

Answer 300

C same for all wavelengths

Question 301

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

Answer 301

C Agitated film evaporator

Question 302

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

Answer 302

C hf < hd

Question 303

Economy of a multiple effect evaporator is not influenced much by the
A rate of heat transfer
B ratio of the weight of the thin liquor to thick liquor
C temperature of the feed
D boiling point elevations

Answer 303

D boiling point elevations

Question 304

The unit of conductance in SI unit is
A W/m
B W/°K
C W/m^2
D W/m°K

Answer 304

B W/°K

Question 305

If Prandtl number is greater than the Schmidt number, then the
A thermal & concentration boundary layers are of equal thickness.
B hydrodynamic(i.e., momentum)boundary layer is thicker than the other two.
C concentration boundary layer lies inside the thermal boundary layer.
D thermal boundary layer lies inside the concentration boundary layer.

Answer 305

D thermal boundary layer lies inside the concentration boundary layer.

Question 306

A dephlegmator is a
A double pipe heat exchanger
B total condenser
C vacuum evaporator
D partial condenser

Answer 306

D partial condenser

Question 307

Which of the following is not used as a medium for high temperature heating ?
A Dowtherm
B liquid metal (e.g. molten sodium)
C fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)
D mercury

Answer 307

D mercury

Question 308

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

Answer 308

B 180

Question 309

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 density
B viscosity
C thermal conductivity
D corrosive nature

Answer 309

B viscosity

Question 310

Rate of heat transfer by vaporisation from pools of water is affected by the
A all of these
B surface tension of water.
C nature of heating surface and distribution of bubbles.
D viscosity of water.

Answer 310

A all of these

Question 311

The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m2.K. At steady state, the temperature of the right face in °C is
A 71.2
B 63.8
C 77.2
D 48.7

Answer 311

D 48.7

Question 312

Vacuum is generally maintained in the vapour space of an evaporator mainly to
A achieve very high concentration of the final product.
B get economical temperature difference by using moderate pressure steam.
C concentrate heat sensitive materials.
D facilitate forward feeding in multiple effect evaporation.

Answer 312

B get economical temperature difference by using moderate pressure steam.

Question 313

Viscosity of gases __________ with increase in temperature.
A increase very rapidly
B decrease slowly
C remain unaffected
D increase slowly

Answer 313

D increase slowly

Question 314

The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.
A sum
B geometric mean
C average
D product

Answer 314

A sum

Question 315

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 either >10 or <10, depends on the mass of the body
D >10

Answer 315

D >10

Question 316

__________ paint has the maximum absorption coefficient.
A Grey
B White
C Black
D Yellow

Answer 316

C Black

Question 317

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 2^0.5
C 2^0.2
D 2^0.8

Answer 317

D 2^0.8

Question 318

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

Answer 318

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

Question 319

The actual temperature drop across the heating surface of an evaporator depends on the
A solution being evaporated.
B pressure difference between the steam chest and the vapor space above the boiling liquid.
C all of these
D liquid depth over the heating surface.

Answer 319

C all of these

Question 320

Intermittant tube cleaning is possible to be done in case of a __________ evaporator.
A none of these
B basket type
C horizontal tube
D calendria

Answer 320

B basket type

Question 321

The unit of heat transfer co-efficient in SI unit is
A J/m°K
B W/m^2°K
C W/m°K
D J/M^2°K

Answer 321

B W/m^2°K

Question 322

During crystallisation, formation of crystal can occur in __________ solution only.
A undersaturated
B supersaturated
C all of these
D saturated

Answer 322

B supersaturated

Question 323

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 40°C
B 25°C
C 35°C
D 30°C

Answer 323

C 35°C

Question 324

In forced convection, the Nusselt number is a function of
A Pr and Gr
B Re and Sc
C Re and Pr
D Re and Gr

Answer 324

C Re and Pr

Question 325

Heat flux is the time rate of heat transfer per unit
A length
B volume
C none of these
D area

Answer 325

D area

Question 326

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

Answer 326

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

Question 327

In which mode of heat transfer, the Biot number is important ?
A Forced convection
B Natural convection
C Transient heat conduction
D Radiation

Answer 327

C Transient heat conduction

Question 328

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

Answer 328

C is thinner than hydrodynamic boundary layer.

Question 329

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is
A dependent on NRe only
B 1.66
C 3.66
D 88.66

Answer 329

C 3.66

Question 330

The absorptivity of a grey body at a given temperature __________ with increasing wavelength of radiation.
A decreases
B may increase or decrease ; depends on the material
C remains constant
D increases

Answer 330

B may increase or decrease ; depends on the material

Question 331

Heat transfer rate described by Fourier’s law will decrease, if the __________ increases.
A temperature difference
B thickness
C heat transfer area
D thermal conductivity

Answer 331

B thickness

Question 332

Which is the most suitable for the con-certration of highly concentrated solution?
A None of these
B Long tube vertical evaporator
C Agitated film evaporator
D Open pan evaporation

Answer 332

D Open pan evaporation

Question 333

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 Colbum jH factor for heat transfer is given by Nst Npr.
C The ratio NNu/NRe . Npr is called the Stanton number.
D The Peclet number is a measure of the ratio of energy transport by convection to that by conduction.

Answer 333

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

Question 334

Mechanical recompression evaporation is used in the production of
A distilled water
B fruits jam
C salt
D alcohol

Answer 334

A distilled water

Question 335

For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area
A remains constant
B increases
C passes through a maxima
D decreases

Answer 335

C passes through a maxima

Question 336

An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporisation of another, is called a
A heat exchanger
B regenerator
C recuperator
D boiler

Answer 336

A heat exchanger

Question 337

Rate of crystallisation does not depend upon the
A none of these.
B turbulence within the solution.
C extent of supersaturation.
D number and active surface area of the crystals.

Answer 337

A none of these.

Question 338

__________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side.
A none of these
B Three pass, fixed tube sheet
C Single pass, fixed tube sheet
D U-tube

Answer 338

D U-tube

Question 339

In SI units, fouling factor is expressed in
A W/m^2°K
B m°K/W
C m^2°K
D m^2°K/W

Answer 339

D m^2°K/W

Question 340

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 0.1
B 0.15
C 0.05
D 0.5

Answer 340

A 0.1

Question 341

For what value of Prandtl number, St = f/2?
A < 1
B 1
C 1.5
D > 1

Answer 341

B 1

Question 342

At what value of Prandtl number, the hydrodynamic and thermal boundary layers are identical ?
A 1
B 0.5
C 1.5
D 80

Answer 342

A 1

Question 343

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

Answer 343

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

Question 344

Pick out the wrong statement:
A Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger.
B Heat sensitive materials should be concentrated in high pressure evaporators.
C Steam jet ejector is used for vapor compression in a thermal recompression evaporator.
D The capacity of an evaporator is reduced by the boiling point elevation.

Answer 344

B Heat sensitive materials should be concentrated in high pressure evaporators.

Question 345

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

Answer 345

A large temperature differentials.

Question 346

Heat transfer rate per unit area is called
A heat transfer co-efficient
B thermal diffusivity
C thermal conductivity
D heat flux

Answer 346

C thermal conductivity

Question 347

In an extended surface heat exchanger, fluid having lower co-efficient
A should not be used as it gives very high pressure drop.
B can flow either inside or outside the tubes.
C flows outside the tubes.
D flows through the tube.

Answer 347

C flows outside the tubes.

Question 348

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 >1
B 1
C <1
D 0

Answer 348

C <1

Question 349

The purpose of providing bleed points in the evaporator is to
A remove the product
B admit the feed
C facilitate removal of non-condensable gases
D create vacuum

Answer 349

C facilitate removal of non-condensable gases

Question 350

Film boiling occurs at __________ pressure.
A sub-atmospheric
B very high
C negative
D atmospheric

Answer 350

B very high

Question 351

Hot water (0.01 m^3 /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/m^3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately
A 50
B 45
C 37
D 32

Answer 351

D 32

Question 352

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

Answer 352

B lower than

Question 353

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

Answer 353

A W/m.k^2

Question 354

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

Answer 354

C give larger area per tube.

Question 355

The equivalent diameter for pressure drop is __________ that for heat transfer.
A equal to
B greater than
C smaller than
D not related with

Answer 355

C smaller than

Question 356

Conductance is given by(where, x = thickness, A = heat flow area, K = thermal conductivity.)
A A/Kx
B K/Ax
C x/KA
D KA/x

Answer 356

D KA/x

Question 357

Water is normally used as a coolant in the heat exchange equipments mainly because ofits
A low density
B abundance & high heat capacity
C low viscosity
D high fluidity

Answer 357

B abundance & high heat capacity

Question 358

For a multipass shell and tube heat exchanger, the LMTD correction factor is always
A 1
B < 1
C between 1 & 2
D > 1

Answer 358

B < 1

Question 359

A diathermaneous substance __________ the thermal radiation completely.
A none of these
B reflects
C transmits
D absorbs

Answer 359

C transmits

Question 360

While the total emissivity of a perfect black body is unity, the same for a real body is
A 1
B 0
C between 0 and 1
D > 1

Answer 360

C between 0 and 1

Question 361

In a forward feed multiple effect evaporator unit
A viscosity of liquid is highest in first effect.
B no pump is required to withdraw the product from the last effect.
C transfer from effect to effect is done by pumps.
D none of these.

Answer 361

D none of these.

Question 362

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 0.0035
D 3.5

Answer 362

B 0.025

Question 363

Unsteady state heat conduction occurs, when
A three dimensional heat flow is concerned.
B temperature distribution is independent of time.
C temperature distribution is dependent on time.
D heat flows in one direction only.

Answer 363

C temperature distribution is dependent on time.

Question 364

What is the unit of thermal conductivity ?
A Kcal/hr. m^2 °C
B Kcal/hr.m.°C
C Kcal/hr.m
D Kcal/hr. °C

Answer 364

B Kcal/hr.m.°C

Question 365

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

Answer 365

A lowest in last effect

Question 366

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 Grashoff
B Stantan
C Brinkman
D Condensation

Answer 366

C Brinkman

Question 367

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

Answer 367

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

Question 368

In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)
A α ≠ 1, ε = 1
B α = 1; ε = 1
C α = 1; ε ≠ 1
D α ≠ 1, ε ≠ 1

Answer 368

B α = 1; ε = 1

Question 369

Fqra cold viscous feed, backward feed gives __________ than forward feed.
A lower economy
B a lower capacity
C a higher capacity
D none of these

Answer 369

C a higher capacity

Question 370

The equation, (1), corrosponds to __________ analogy.
A Colburn
B Reynolds
C Prandtl
D Von-Karmann

Answer 370

C Prandtl

Question 371

Pick out the wrong statement.
A The emissivity of a surface increases with increase in surface roughness.
B The emissivity of a surface decreases, if it gets corroded by atmospheric environment.
C The emissivity of a polished surface is quite low.
D The emissivity of a non-metallic surface decreases with increase in the temperature.

Answer 371

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

Question 372

Stefan-Boltzman law which describes the radiation heat transfer states that, it is proportional to (where, t = temperature in °C T = absolute temperature in ° K )
A T^4
B t^4
C 1/T^4
D 1/t^4

Answer 372

A T^4

Question 373

The main function of baffles provided in a shell and tube heat exchanger is to
A facilitate the cleaning of outer tube surface.
B all of these
C hold the tubes in position.
D enhance turbulence.

Answer 373

D enhance turbulence.

Question 374

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 1.741 h1
B 0.574 h1
C 0.794 h1
D 1.26 h1

Answer 374

C 0.794 h1

Question 375

In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used
A to prevent corrosion of the tube bundles.
B because of its low cost.
C in low range of temperature differences.
D in high range of temperature differences.

Answer 375

D in high range of temperature differences.

Question 376

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

Answer 376

B all

Question 377

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

Answer 377

B forced convection and conduction.

Question 378

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

Answer 378

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

Question 379

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

Answer 379

A flexibility possible in the baffle arrangement.

Question 380

Duhring’s plot’ is of use in
A absorption
B leaching
C evaporation
D extractive distillation

Answer 380

C evaporation

Question 381

The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoffs law.
A none of these
B nature of the body
C wavelength of radiation
D temperature of the body

Answer 381

D temperature of the body

Question 382

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

Answer 382

B steam jacketed kettle

Question 383

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 0.6
B 0.4
C 0.2
D 0.8

Answer 383

A 0.6

Question 384

Correction is applied to LMTD for __________ flow.
A cross
B counter
C none of these
D parallel

Answer 384

A cross

Question 385

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

Answer 385

A boiling point

Question 386

In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer co-efficient
A is not affected
B increases
C decreases
D may increase or decrease; depends on the feed

Answer 386

C decreases

Question 387

The characteristic dimensionless groups for heat transfer to a fluid flowing through a pipe in laminar flow are
A Nu, Pr
B Nu, Pr, Re
C Re.Gz
D Nu, Gz

Answer 387

D Nu, Gz

Question 388

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

Answer 388

D Δt^5/4

Question 389

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 3.97
C none of these
D 970

Answer 389

A 180

Question 390

The Grashoff number is defined as the ratio of the
A buoyancy to viscous forces.
B inertial to viscous forces.
C buoyancy to inertial forces.
D buoyancy to surface tension forces.

Answer 390

A buoyancy to viscous forces.

Question 391

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

Answer 391

A more space.

Question 392

1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C.
A 1
B none of these
C 1.49
D 4.88

Answer 392

C 1.49

Question 393

Pick out the wrong statement.
A 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 wavelength of 0.5 λ1.
B In process heat exchangers, saturated steam is preferred over the superheated steam.
C 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 the entire wavelength range is equal to emissivity.
D 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.

Answer 393

A 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 wavelength of 0.5 λ1.

Question 394

Which of the following forced convection heat transfer equation accounts for the liquid viscosity effect for viscous liquids ?
A Nusselt equation
B None of these
C Sieder-Tate equation
D Dittus-Boeltier equation

Answer 394

C Sieder-Tate equation

Question 395

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

Answer 395

C loosing sensible heat.

Question 396

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 parabolic
B linear
C logarithmic
D hyperbolic

Answer 396

B linear

Question 397

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

Answer 397

B 7

Question 398

Overall heat transfer co-efficient for cooling of hydrocarbons by water is about
A 50 -100 BTU/hr. ft.^2°F
B 1000 - 1500 BTU/hr. ft.^2°F
C 50 -100 W/m^2 . °K
D 50 -100 Kcal/hr.m^2.°C

Answer 398

A 50 -100 BTU/hr. ft.^2°F

Question 399

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

Answer 399

B high proportion of air space.

Question 400

The sum of reflectivity and absorptivity for an opaque body is equal to
A 0
B 1
C 0.5
D 2

Answer 400

B 1

Question 401

What is the steam economy in case of a single effect evaporator system ?
A < 1
B 1
C 0.1
D >1

Answer 401

A < 1

Question 402

Which of the following is correct ?
A Resistance = Driving force x Rate
B Rate = Driving force x Resistance
C Rate = Resistance/Driving force
D Driving force = Rate x Resistance

Answer 402

D Driving force = Rate x Resistance

Question 403

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

Answer 403

D 0.6 to 120

Question 404

Double pipe heat exchangers are used
A when heat transfer area required is very low, i.e (100-200 ft^2).
B because it is less costly.
C because it occupies less floor area.
D when heat transfer area required is very high.

Answer 404

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

Question 405

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.

Answer 405

B exit fluid temperature = wall temperature.

Question 406

In a forward feed multiple effect, the pressure build up will be
A highest at the outlet of the last effect.
B highest at the inlet of the last effect. C least at the inlet of the first effect.
D least at the outlet of the last effect.

Answer 406

D least at the outlet of the last effect.

Question 406

At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid flowing through a heated pipe ?
A < 0.1
B > 0.6
C < 0.5
D 0.5

Answer 406

B > 0.6

Question 407

Radiant energy received by a body is proportional to (where, d = the distance between the object emitting radiation and that receiving it.)
A √d
B d
C d^2
D d^1.5

Answer 407

C d^2

Question 408

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 hyperbolic
B logarithmic
C parabolic
D linear

Answer 408

C parabolic

Question 408

Dietus-Boelter equation cannot be used for molten metals mainly due to its very low
A viscosity
B Prandtl number
C Grashoff number
D thermal conductivity

Answer 408

B Prandtl number

Question 409

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 < 0.50
C < 0.25
D < 0.75

Answer 409

D < 0.75

Question 410

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

Answer 410

C Filmwise condensation takes place on non-wettable surfaces.

Question 411

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

Answer 411

D volume to surface area

Question 412

Dropwise condensation occurs on __________ surfaces.
A smooth clean
B polished
C clean and dirt free
D contaminated cooling

Answer 412

D contaminated cooling

Question 413

Thermal diffusivity is the most important in heat transfer by
A natural convection
B conduction
C condensation
D radiation

Answer 413

B conduction

Question 414

Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when Prandtl number is
A < 1
B 0.1
C >1
D l

Answer 414

B 0.1

Question 415

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 none of these.
D surface area and temperature of the heat source.

Answer 415

C none of these.

Question 416

Peclet number (Pe) is given by
A Pe = Re/Pr
B Pe = Re.Pr
C Pe = Nu.Re
D Pe = Pr/Re

Answer 416

B Pe = Re.Pr

Question 417

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 1/A
B 1/ρ
C t
D all of these

Answer 417

D all of these

Question 418

Reynold’s analogy states that
A NNu α f
B Nst α NRe
C NRe α f
D Nst α f

Answer 418

D Nst α f

Question 419

When does the heat generated by fluid friction becomes appreciable compared to the heat transferred between the fluids ?
A At high fluid velocity
B None of these
C When fluid flows past a smooth surface
D At low velocity

Answer 419

A At high fluid velocity

Question 420

Nusselt number for full developed, laminar, constant property flow in a pipe at uniform heat flux is
A 4.364
B 0.72
C 18
D 83

Answer 420

A 4.364

Question 421

The main purpose of providing fins on heat transfer surface is to increase the
A temperature gradient.
B heat transfer area.
C heat transfer co-efficient.
D mechanical strength of the equipment.

Answer 421

B heat transfer area.

Question 422

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

Answer 422

B increases.

Question 423

Tube expansion allowances exist in __________ heat exchanger.
A U-tube
B none of these
C single pass fixed tube sheet
D multipass fixed tube sheet

Answer 423

A U-tube

Question 424

In natural convection heat transfer, the correlating parameter is the
A Grashoff number
B Graetz number
C Bond number
D Eckert number

Answer 424

A Grashoff number

Question 425

For gases, the thermal conductivity increases with temperature rise. For liquids, with increase in concentration, its thermal conductivity generally
A decreases
B increases exponentially
C remains unchanged
D increases

Answer 425

A decreases

Question 426

Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called
A forced convection
B natural convection
C conduction
D radiation

Answer 426

A forced convection

Question 427

A __________ surface has the maximum thermal emissivity out of the following.
A white & rough
B black & rough
C white & smooth
D black & smooth

Answer 427

B black & rough

Question 428

In a co-current double pipe heat exchanger used for condensing saturated steam over the inner tube, if the entrance and exit conditions of the coolant are interchanged, then the rate of condensation will
A increase
B either increase or decrease; depends on the coolant flow rate
C remain unchanged
D decrease

Answer 428

C remain unchanged

Question 429

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

Answer 429

B direct contact

Question 430

The Stefan-Boltzman constant depends on the
A medium
B temperature
C none of these
D surface

Answer 430

C none of these

Question 431

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

Answer 431

B constant temperature equal to that of the base

Question 432

Which one gives the monochromatic emissive power for black body radiation ?
A Stefan-Boltzman law
B Wien’s law
C Planck’s law
D Kirchhoffs law

Answer 432

C Planck’s law

Question 433

Nucleate boiling is promoted
A in the absence of agitation
B on polished surfaces
C on rough surfaces
D none of these

Answer 433

C on rough surfaces

Question 434

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the
A temperature gradient produced due to density difference
B buoyancy of the bubbles produced at active nucleation site.
C none of these.
D existence of thermal boundary layer.

Answer 434

C none of these.

Question 435

Leidenfrost point is a term concerned with the
A boiling of a liquid on a hot surface.
B condensation of the saturated vapor on a cold surface.
C heat transfer between two highly viscous liquids.
D concentration of a corrosive solution by evaporation.

Answer 435

A boiling of a liquid on a hot surface.

Question 436

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 95
B 70
C 40
D 50

Answer 436

B 70

Question 437

A multiple effect evaporator as compared to a single effect evaporator of the same capacity has
A higher steam economy.
B lower steam economy.
C lower heat transfer area.
D higher solute concentration in the product.

Answer 437

A higher steam economy.

Question 438

The local surface conductance for laminar film condensation on vertical surface is (where, t = film thickness)
A ∝ t
B independent of ‘t’
C ∝ √t
D ∝ 1/t

Answer 438

D ∝ 1/t

Question 439

Heat transfer in the laminar sublayer in case of a liquid flowing through a pipe, is mostly by
A convection
B conduction
C eddies current
D none of these

Answer 439

B conduction

Question 440

Natural convection is characterised by
A Peclet number
B Grashhoff number
C Prandtl number
D Reynolds number

Answer 440

B Grashhoff number

Question 441

Terminal point temperature differences between fluids in case of a heat exchanger is termed as
A arithmetic mean temperature difference.
B approach.
C geometric mean temperature difference.
D log mean temperature difference.

Answer 441

B approach.

Question 442

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 160
B 133
C 125
D 150

Answer 442

A 160

Question 443

Planck’s distribution law is valid for __________ bodies.
A all of these
B coloured
C black
D white

Answer 443

B coloured

Question 444

The Graetz number is concerned with the
A heat transfer in turbulent flow.
B heat transfer in laminar flow.
C absorption with chemical reaction.
D mass transfer between a gas and a liquid.

Answer 444

B heat transfer in laminar flow.

Question 445

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

Answer 445

A Long tube vertical evaporator

Question 446

Stefan-Boltzman law applies to __________ body.
A black
B grey
C any colour
D white

Answer 446

A black

Question 447

If average heat transfer co-efficient is ha and the local coefficient at the end of the plate is hl then in case of heat transfer to a fluid flowing over a flat plate, heated over its entire length
A ha = hl
B ha = 2hl
C ha = 0.5 hl
D ha = 0.75 hl

Answer 447

B ha = 2hl

Question 448

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

Answer 448

A material is anisotropic.

Question 449

An ejector is used to
A increase pressure
B remove condensate
C increase temperature
D none of these

Answer 449

D none of these

Question 450

Dropwise condensation is promoted on a/an __________ surface.
A glazed
B oily
C coated
D smooth

Answer 450

B oily

Question 451

In a shell and tube heat exchanger,
A the temperature drops in the two fluids and the wall are proportional to individual resistances.
B there is no relationship between temperature drop and resistance.
C the relationship is not generalised.
D the temperature drop is inversely proportional to the resistance across which the drop occurs.

Answer 451

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

Question 452

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

Answer 452

D varies directly as the area and the LMTD.

Question 453

View factor is important in heat transfer by
A radiation
B natural convection
C forced convection
D steady state conduction

Answer 453

A radiation

Question 454

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 unpredictable
D same

Answer 454

B less

Question 455

Film condensation is promoted on a/an __________ surface.
A dirty
B oily
C clean & smooth
D coated

Answer 455

C clean & smooth

Question 456

The purpose of providing a ‘catchall’ in the vapor line of an evaporator is to
A vent the non-condensible gases
B arrest the entrained liquid
C create vacuum
D regulate the vapor flow

Answer 456

B arrest the entrained liquid

Question 457

Duhring rule is important in solving problems on
A crystallisation
B humidification
C evaporation
D distillation

Answer 457

C evaporation

Question 458

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

Answer 458

B heat transfer area

Question 459

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

Answer 459

C thermal conductivity

Question 460

Pick out the wrong statement.
A S.I. unit of fouling factor is Watt/m^2.°K.
B Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient.
C In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles.
D Longitudinal fins are used in extended surface heat exchangers, when the direction of fluid flow is parallel to the axis of the tube.

Answer 460

A S.I. unit of fouling factor is Watt/m^2.°K.

Question 461

(NGr x NPr) is called the __________ number.
A Stanton
B Nusselt
C Graetz
D Reyleigh

Answer 461

D Reyleigh

Question 462

In a single evaporator system, the steam economy __________ by creating vacuum in the evaporator.
A may increase or decrease, depends on the vacuum
B decreases
C increases
D remains constant

Answer 462

C increases

Question 463

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

Answer 463

C gives a lower shell side pressure drop.

Question 464

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/m^3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m^2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
A 0.55
B 0.15
C 55.5
D 555

Answer 464

B 0.15

Question 465

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 40 minutes
D 20 minutes

Answer 465

A 5 minutes

Question 466

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

Answer 466

B natural convection

Question 467

Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
A none of these.
B tube diameter & pitch.
C baffle spacing & shell diameter.
D viscosity, density & mass velocity of shell side fluid.

Answer 467

A none of these.

Question 468

For evaporation of viscous solution in a multiple effect evaporator, the prefered feeding scheme is
A none of these
B forward
C parallel
D backward

Answer 468

D backward

Question 469

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 T^4
C independent of T
D α 1/T

Answer 469

D α 1/T

Question 470

In a heat exchanger, floating head is provided to
A increase the heat transfer area.
B relieve stresses caused by thermal expansion.
C increase log mean temperature gradient.
D facilitate cleaning of the exchanger.

Answer 470

B relieve stresses caused by thermal expansion.

Question 471

Pick out the wrong statement.
A 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.
B Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted.
C In case of short tube vertical evaporators, area of central downtake is about 50 to 100% of the total tube cross-sectional area.
D Solvates’ are chemical compounds formed by solute with their solvents. When water is the solvent, then it is called a ‘hydrate’.

Answer 471

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

Question 472

With increase in temperature, the total emissivity of conductors
A increases
B decreases linearly
C decreases
D remains same

Answer 472

A increases

Question 473

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 no effect on economy
D lower capacity

Answer 473

A increased economy

Question 474

Which of the following has the minimum absorptivity ?
A Iron plates
B Coal dust
C Aluminium foil
D Refractory bricks

Answer 474

C Aluminium foil

Question 475

Electro-magnetic spectrum range, which is important for radiation varies from __________ microns.
A 1 to 100
B 0.5 to 50
C 100 to 1000
D 10 to 100

Answer 475

B 0.5 to 50

Question 476

In SI units, thermal conductivity is expressed in
A Watt/m^2. °K
B Watt/m^4. °K
C Watt/m.°K
D Watt/m^2. °K

Answer 476

C Watt/m.°K

Question 477

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

Answer 477

B I^2R

Question 478

Water always boils when its
A temperature reaches 100° C.
B saturated vapour pressure is less than the atmospheric pressure.
C saturated vapour pressure equals the external pressure on its surface.
D vapour pressure equals 76 cm of Hg.

Answer 478

C saturated vapour pressure equals the external pressure on its surface.