Heat Transfer Flashcards by Study Monster

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

B create more suction head.

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

C Prandtl

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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.

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

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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

D d^-0.2

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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

A increases

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

D super-saturation

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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.

B an oily surface.

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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

B (ΔT)^3/4

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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

A vacuum

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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

C evaporate the water.

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

D < 1

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

C Dirhing’s

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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.

A keeping the heat transfer surface clean.

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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

165.4

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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

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

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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

D BTU/hr. ft^2°F

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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

B falling film

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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

D 12

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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.

C large scale evaporation of liquor is needed.

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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

C 333W/m^2.K

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

C vacuum

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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.

D 85% magnesia cement and glass wool.

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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

B U1 = U2

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

Prandtl

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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.

A all of these

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

D the largest

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

B increase by 2^16

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

D saturated

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.

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

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

C White lead

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

B 2

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.

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

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

A heat transfer co-efficient

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.

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

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

D transmissivity = 1

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.

B vertical heat exchanger with steam on shell side.

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.

C painting the surface white (with aluminium paint).

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

B 5000

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

B (ΔT)^3

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.

A infinity.

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

A none of these

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

D f/2

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

A first increase and then decrease

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

D linear

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

A decreases

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.

B Swenson-Walker crystalliser is a batch crystalliser.

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

A Sphere

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

A 2

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

B all of these

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.

B all of these

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

D increased

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

D viscous

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

D increasing temperature.

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

B agitated film

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

B zero

"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

D Kirchoffs

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

A 43.75

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.

A higher tube side heat transfer co-efficient.

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

D radiation becomes important

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.

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

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

B viscous

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.

A called the angle of vision.

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

A (D))^-0.2

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.

A all of these

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

C 0.72

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.

D less than that of the uninsulated steam pipe.

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 ∞

B < 1

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

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

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

D current

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

A straight line

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.

A all of these

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

C 3 x l0^8

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

D burnout

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

A (ΔT)1/4

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

A density

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

B decreases

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.

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

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

C 5000-15000

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

B decreases

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

B all of these

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

C R2/(R1+R2)

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

D entrainment separator

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.

B increases.

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

B 0.2 D

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

D 0.5-50

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

C nucleate boiling

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

C logarithmic

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.

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.

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

C decreases

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.

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

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

A equal to

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

C Nitrogen

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

D less

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.

D most concentrated liquid is at highest temperature.

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

B logarithmic

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

A Thermal diffusivity/Momentum diffusivity

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

A 1

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

C 44930

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.

A momentum diffusivity to thermal diffusivity.

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)

D boiling point (at the same pressure)

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

D Graetz

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

A local

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.

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

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

A transient conduction

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.

A goes through a minimum.

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

D Grashoff

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.

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

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)

D mixed convection (both free and forced)

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

D vertical

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.

D Constant rate of fluid flow.

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.

C foaming of the solution.

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

D none of these

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

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

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.

B accounts for additional resistances to heat flow.

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

D sum

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.

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

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

B C/E

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

C horizontal tube

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

D Reynolds

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.

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

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.

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

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.

C all of these

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

A convection

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

A 1

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

C partial ionisation

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

A radiation

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.

B all of these

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

A Δt

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

A Silver

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

C 4000

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

C 0.6 to 120

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

A Iron

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

D conduction

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

A None of these

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.

D resistances in series.

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

C 16.5 kW/m^2

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.

C remove condensate and inert gases.

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

A 400

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

B 1 and 0

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.

D for fluids in tubulent flow.

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

A low film co-efficient

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

A excessive corrosion

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.

C both counter and parallel-flow of the fluids.

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

C Wien's

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.

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

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.

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

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.

D momentum diffusivity to thermal diffusivity.

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.

B multiple effect evaporator.

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

A turbulent

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.

C all of these

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

C tube diameter

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.

A is smaller than that of II.

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

A kA < 0.5kB

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

C economy

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

C 1-1 heat exchanger

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

D that across the entire pipe

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.

A increase the steam economy & the capacity.

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.

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

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.

D requirement of heat transfer area is low.

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.

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

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

C increases

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

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

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

D Series and parallel set of shell and tube

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

C ha = 2hL

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

C parabolic

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.

B remove non-condensable gases.

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

D decrease

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.

C counter flow with process stream on shell side.

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

D concentrations

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

C 1

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

D Grashhoff number

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

C basket type

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

B Air

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

D different

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

C Grashoff number

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.

B Reynolds number for the flow involved is < 2100.

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

C more

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

B high

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.

D feed flows from low pressure to high pressure.

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.

B increase the shell side heat transfer co-efficient.

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

C decreases

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

D cube

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

C capacity

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

D 1

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

B condensate

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.

C condensate is corrosive in nature.

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

A four times

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

C decreases

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

B low thermal conductivity.

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.

C avoid buckling of tubes.

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

C Lewis relationship

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

C 1

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

B film

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.

C high co-efficient of thermal expansion.

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

D 0°K

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

A 0.45

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.

A results in making part of the heating surface inactive.

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

C 0.7

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

C reduce the capacity

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

A > 1

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

B NPr^1/3

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.

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

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.

D factor of safety.

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.

A 4.88 kcal/hr. m.^2°C.

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

B 5.6697 x 1^0-8W/m^2.°K^4

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

D decrease

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

B turbulent

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.

A logarithmic mean temperature difference.

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.

C double pipe type with fin on air side.

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

C Logarithmic mean area

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

A t = 800 s

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

D oily

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

A gD^3.β.Δtρ^2/μ^2

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

D black & rough

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

D Prandtl

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.

D decreased capacity.

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

A always between h1 and h2

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

A D/5 and D

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.

C both the tube sheets fixed.

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

C none of these

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

A steam economy

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

B 34.4

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

D Newton's law of cooling

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

B 0.75 D

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

D all of these

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

D 3.06 x l0^5

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

A pool

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

D increases

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

A highly viscous

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.

D remove water resulting from partial condensation of steam.

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

A 4.36

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

D film

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

C Backward feed

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

D all bodies

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

C > 10000

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

D 4^0.8

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

D twice

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

A P and S

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

A Double pipe

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

A Interfacial tension

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

D cross-sectional area

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

A lead

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

D Liquid metal

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.

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

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.

A Temperature difference between the two surfaces of the wall.

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.

A solution has an elevation of boiling point.

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

A Colburn

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

C Wien's displacement

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.

B increasing temperature of the vapour.

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.

A sum of all resistances.

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

A Triangular pitch

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

B both(a) & (b)

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.

C there is no risk of contamination.

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.

A and the wall are proportional to individual resistances.

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

A 1

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

D Black paint

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

B 1-1.3

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

A Catchall

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

A absorptivity = 1

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

D 1

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.

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

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

D Reynolds

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.

C decreases.

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

C density

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

A none of these

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

B Re, Pr

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

B zero

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

B 1000

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

D exothermic

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.

C all of these

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

B 6.1

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.

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

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

A same in either 'a', b' or 'c'

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.

A none of these.

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.

A Schmidt number.

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

C 5 to 10

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

D coke breeze

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.

A increases the overall heat transfer coefficient.

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

A cummulatively increases

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

C Lee's

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

D Planck's

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

B 51 min

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

D K/h0

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.

C under thermal equilibrium.

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.

A shape and porosity of the body.

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

A r = k/h

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

B < 1

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.

B none of these.

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

D Schmidt number

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

D create vacuum.

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

24000

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

D 0

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

A Steel

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

A 2K/h0

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

D W^-1m^2K

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

C all of these

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.

C more than 45°C

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

C Nusselt

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

C same for all wavelengths

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

C Agitated film evaporator

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

C hf < hd

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

D boiling point elevations

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

B W/°K

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.

D thermal boundary layer lies inside the concentration boundary layer.

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

D partial condenser

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

D mercury

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

B 180

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

B viscosity

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.

A all of these

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

D 48.7

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.

B get economical temperature difference by using moderate pressure steam.

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

D increase slowly

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

A sum

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

D >10

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

C Black

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

D 2^0.8

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.

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

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.

C all of these

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

B basket type

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

B W/m^2°K

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

B supersaturated

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

C 35°C

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

C Re and Pr

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

D area

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.

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

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

C Transient heat conduction

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.

C is thinner than hydrodynamic boundary layer.

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

C 3.66

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

B may increase or decrease ; depends on the material

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

B thickness

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

D Open pan evaporation

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.

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

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

A distilled water

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

C passes through a maxima

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

A heat exchanger

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.

A none of these.

__________ 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

D U-tube

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

D m^2°K/W

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

A 0.1

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

B 1

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

A 1

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

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

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.

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

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.

A large temperature differentials.

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

C thermal conductivity

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.

C flows outside the tubes.

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

C <1

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

C facilitate removal of non-condensable gases

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

B very high

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

D 32

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

B lower than

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

A W/m.k^2

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.

C give larger area per tube.

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

C smaller than

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

D KA/x

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

B abundance & high heat capacity

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

B < 1

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

C transmits

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

C between 0 and 1

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.

D none of these.

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

B 0.025

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.

C temperature distribution is dependent on time.

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

B Kcal/hr.m.°C

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

A lowest in last effect

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

C Brinkman

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.

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

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

B α = 1; ε = 1

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

C a higher capacity

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

C Prandtl

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.

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

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

A T^4

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.

D enhance turbulence.

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

C 0.794 h1

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.

D in high range of temperature differences.

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

B all

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.

B forced convection and conduction.

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.

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

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.

A flexibility possible in the baffle arrangement.

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

C evaporation

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

D temperature of the body

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

B steam jacketed kettle

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

A 0.6

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

A cross

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

A boiling point

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

C decreases

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

D Nu, Gz

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

D Δt^5/4

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

A 180

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.

A buoyancy to viscous forces.

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.

A more space.

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

C 1.49

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.

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.

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

C Sieder-Tate equation

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.

C loosing sensible heat.

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

B linear

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

B 7

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

A 50 -100 BTU/hr. ft.^2°F

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.

B high proportion of air space.

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

B 1

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

A < 1

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

D Driving force = Rate x Resistance

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

D 0.6 to 120

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.

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

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.

B exit fluid temperature = wall temperature.

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.

D least at the outlet of the last effect.

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

B > 0.6

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

C d^2

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

C parabolic

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

B Prandtl number

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

D < 0.75

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:

C Filmwise condensation takes place on non-wettable surfaces.

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

D volume to surface area

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

D contaminated cooling

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

B conduction

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

B 0.1

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.

C none of these.

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

B Pe = Re.Pr

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

D all of these

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

D Nst α f

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

A At high fluid velocity

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

A 4.364

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.

B heat transfer area.

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.

B increases.

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

A U-tube

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

A Grashoff number

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

A decreases

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

A forced convection

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

B black & rough

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

C remain unchanged

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

B direct contact

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

C none of these

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.

B constant temperature equal to that of the base

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

C Planck's law

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

C on rough surfaces

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.

C none of these.

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.

A boiling of a liquid on a hot surface.

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

B 70

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.

A higher steam economy.

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

D ∝ 1/t

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

B conduction

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

B Grashhoff number

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.

B approach.

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

A 160

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

B coloured

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.

B heat transfer in laminar flow.

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

A Long tube vertical evaporator

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

A black

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

B ha = 2hl

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.

A material is anisotropic.

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

D none of these

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

B oily

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.

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

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.

D varies directly as the area and the LMTD.

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

A radiation

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

B less

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

C clean & smooth

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

B arrest the entrained liquid

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

C evaporation

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

B heat transfer area

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

C thermal conductivity

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.

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

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

D Reyleigh

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

C increases

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.

C gives a lower shell side pressure drop.

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

B 0.15

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

A 5 minutes

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

B natural convection

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.

A none of these.

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

D backward

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

D α 1/T

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.

B relieve stresses caused by thermal expansion.

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'.

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

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

A increases

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

A increased economy

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

C Aluminium foil

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

B 0.5 to 50

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

C Watt/m.°K

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

B I^2R

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.

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

Heat Transfer Flashcards

(480 cards)