flashcard HT

Question 1

Crystal size in a continuous crystalliser depends upon the A. rate of heat transfer. B. degree of turbulence. C. degree of supersaturation. D. all (a) (b) and (c).

Answer 1

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

Question 2

Heat waves A. can not pass through vacuum. B. travel in straight line. C. can be reflected by a mirror. D. both (b) and (c).

Answer 2

D. both (b) and (c).

Question 3

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

Answer 3

C. double pipe type with fin on air side.

Question 4

Which of the following is generally considered as opaque surface towards radiations? A. Gases B. Solids C. Liquids D. Both (b) and (c).

Answer 4

D. Both (b) and (c).

Question 5

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

Answer 5

C. multiple effect evaporator.

Question 6

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

Answer 6

B. nucleate boiling

Question 7

Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are capacity the economy of the evaporator respectively) A. C/E B. E/C C. CE D. 1/CE

Answer 7

A. C/E

Question 8

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

Answer 8

A. Nst ? f

Question 9

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

Answer 9

B. increases

Question 10

Fourier’s law applies to the heat transfer by A. convection B. radiation C. conduction D. all (a), (b) & (c)

Answer 10

C. conduction

Question 11

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

Answer 11

D. none of these.

Question 12

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

Answer 12

C. logarithmic mean temperature difference.

Question 13

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

Answer 13

B. decreases

Question 14

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

Answer 14

A. absorptivity = 1

Question 15

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 accelerati

Answer 15

B. 34.4

Question 16

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

Answer 16

C. accounts for additional resistances to heat flow.

Question 17

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

Answer 17

B. decreases

Question 18

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

Answer 18

B. create vacuum.

Question 19

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

Answer 19

D. passes through a maxima

Question 20

The thermal efficiency of a reversible heat engine operating between two given thermal reservoirs is 0.4. The device is used either as a refrigerator or as a heat pump between the same reservoirs. Then the coefficient of performance as a refrigerator (COP

Answer 20

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

Question 21

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

Answer 21

A. 32

Question 22

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

Answer 22

C. relieve stresses caused by thermal expansion.

Question 23

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

Answer 23

D. boiling of a liquid on a hot surface.

Question 24

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

Answer 24

A. counter flow with process stream on shell side.

Question 25

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

Answer 25

B. I^2R

Question 26

Pick out the wrong statement. A. Orifice baffles are never used in a shell and tube heat exchanger. B. Pressure drop on the shell side of a heat exchanger depends upon tube pitch also. C. In a horizontal tube evaporator, surface blanketing by

Answer 26

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

Question 27

Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone. A. laminar B. transition C. both ‘a’ & ‘b’ D. highly turbulent

Answer 27

D. highly turbulent

Question 28

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

Answer 28

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

Question 29

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

Answer 29

B. mercury

Question 30

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

Answer 30

D. none of these.

Question 31

Kirchoff s law applies to __________ radiation. A. total B. monochromatic C. both (a) & (b) D. neither (a) nor (b)

Answer 31

C. both (a) & (b)

Question 32

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

Answer 32

A. increases.

Question 33

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

Answer 33

C. foaming of the solution.

Question 34

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

Answer 34

C. increase the shell side heat transfer co-efficient.

Question 35

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

Answer 35

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

Question 36

The unit of heat transfer co-efficient in SI unit is A. J/M2 K B. W/m2 K C. W/m K D. J/m K

Answer 36

B. W/m2 K

Question 37

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

Answer 37

C. economy

Question 38

Pick out the wrong statement. A. In case of heat transfer by purely forced convection, GR/Re2 ? 1. B. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as ‘x’) is equal to 4x. C. Distillation process

Answer 38

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

Question 39

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

Answer 39

A. boiling point elevations

Question 40

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

Answer 40

A. decreased capacity.

Question 41

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

Answer 41

A. smaller than

Question 42

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

Answer 42

C. the largest

Question 43

The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K= 0.04 W/m. K and thickness 0.16m is 10 W/m2. The temperature of the inside wall is - 5 C. The outside wall temperature is A. 25 C B. 30 C C. 35 C

Answer 43

C. 35 C

Question 44

Thermal conductivity of a conducting solid material depends upon its A. temperature B. porosity C. both (a) & (b) D. neither (a) nor (b)

Answer 44

C. both (a) & (b)

Question 45

Pick out the wrong statement. A. The controlling resistance in case of heating of air by condensing steam is in the air film. B. The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one o

Answer 45

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

Question 46

The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ?T = Temperature drop across condensate film) A. (?T)^2 B. sqrt*?T C. (?T)^1/4 D. (?T)^3/2

Answer 46

C. (?T)^1/4

Question 47

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is A. in the central core of the fluid. B. uniformly distributed throughout the fluid. C. mainly confined to a thin film of fluid near the surf

Answer 47

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

Question 48

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

Answer 48

A. Lewis relationship

Question 49

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides A. higher economy B. lower capacity C. both (a) & (b) D. lower economy

Answer 49

A. higher economy

Question 50

A 10 cm dia steam pipe, carrying steam at 180 C, is covered with an insulation (conductivity = 0.6 W/m. C). It losses heat to the surroundings at 30 C. Assume a heat transfer co-efficient of 0.8 W/m2. C for heat transfer from surface to the surroundings.

Answer 50

B. less than that of the uninsulated steam pipe.

Question 51

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

Answer 51

A. Logarithmic mean area

Question 52

Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer can not take place A. between two bodies in physical contact with each other. B.

Answer 52

B. between two bodies not in physical contact with each other.

Question 53

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

Answer 53

C. Schmidt number.

Question 54

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

Answer 54

A. give larger area per tube.

Question 55

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

Answer 55

D. may increase or decrease ; depends on the material

Question 56

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

Answer 56

A. Planck’s law

Question 57

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

Answer 57

B. 1

Question 58

In a shell and tube heat exchanger, A. the temperature drops in the two fluids and the wall are proportional to individual resistances. B. the temperature drop is inversely proportional to the resistance across which the drop occurs. C. there

Answer 58

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

Question 59

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

Answer 59

B. for fluids in tubulent flow.

Question 60

The equation, Nst = (f/2)/(1+5(NPr - 1)(sqrt*f/2)), corrosponds to __________ analogy. A. Von-Karmann B. Reynolds C. Colburn D. Prandtl

Answer 60

D. Prandtl

Question 61

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

Answer 61

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

Question 62

Out of the following four assumptions used in the derivation of the equation for LMTD [LMTD = (?t1 - ?t2)/(ln(?t1/?t2))], which one is subject to the largest deviation in practice ? A. Constant overall heat transfer co-efficient. B. Constant rate

Answer 62

B. Constant rate of fluid flow.

Question 63

Heat flux increases with temperature drop beyond the Leiden frost point in the plot of heat flux vs. temperature drop for a boiling liquid, because A. convection becomes important B. conduction becomes important C. radiation becomes important

Answer 63

C. radiation becomes important

Question 64

Resistance to heat flow by conduction is proportional to (where, t & ? are thickness & density of the material respectively and A = area normal to the direction of heat flow.) A. t B. 1/? C. 1/A D. all (a), (b) & (c)

Answer 64

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

Question 65

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

Answer 65

D. linear

Question 66

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it A. decreases the pressure drop. B. decreases the outlet temperature of cooling medium. C. increas

Answer 66

C. increases the overall heat transfer coefficient.

Question 67

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

Answer 67

D. film

Question 68

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

Answer 68

A. 0.2 D

Question 69

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

Answer 69

B. T^4

Question 70

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

Answer 70

B. 4.36

Question 71

What is the unit of thermal conductivity? A. Kcal/hr. m2 C B. Kcal/hr.m. C C. Kcal/hr.m D. Kcal/hr. C

Answer 71

B. Kcal/hr.m. C

Question 72

The thermal radiation emitted by a body is proportional to T^n, where T is its absolute temperature. The value of ‘n’ is exactly 4 for A. black painted bodies B. all bodies C. polished bodies only D. a black body

Answer 72

B. all bodies

Question 73

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

Answer 73

C. low film co-efficient

Question 74

It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30 C. The boiling point of the solution is 110 C, the latent heat of vaporisation is 2100 kJ/k

Answer 74

A. 3.06 x 10^5

Question 75

LMTD for counterflow and prallel flow heat exchanger will be the same, when the A. cold fluid is heated to a certain temperature by condensing steam (isothermal fluid). B. outlent temperature of both the hot and cold fluid are same. C. outlet

Answer 75

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

Question 76

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

Answer 76

B. NPr^1/3

Question 77

The range of electromagnetic spectrum important in heat transfer by radiation is __________ microns. A. 0.38-0.78 B. 0.5-50 C. 100-1000 D. 5-50

Answer 77

B. 0.5-50

Question 78

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

Answer 78

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

Question 79

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

Answer 79

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

Question 80

Economy of a multiple effect evaporator depends upon the A. heat balance consideration B. rate of heat transfer C. both (a) and (b) D. neither (a) nor (b)

Answer 80

A. heat balance consideration

Question 81

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

Answer 81

D. heat transfer in laminar flow.

Question 82

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

Answer 82

B. called the angle of vision.

Question 83

Pick out the wrong statement. A. The emissivity of a surface decreases, if it gets corroded by atmospheric environment. B. The emissivity of a surface increases with increase in surface roughness. C. The emissivity of a polished surface is qui

Answer 83

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

Question 84

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

Answer 84

A. Re, Pr

Question 85

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

Answer 85

B. decreases

Question 86

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

Answer 86

D. radiation

Question 87

Pick out the correct statement. A. Higher is the temperature of the radiating body, higher is the wavelength of radiation. B. Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder. C. The wavelength c

Answer 87

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

Question 88

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

Answer 88

B. in high range of temperature differences.

Question 89

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

Answer 89

A. black

Question 90

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

Answer 90

C. some

Question 91

A perfect black body is a perfect __________ of radiation. A. absorber B. emitter C. both (a) & (b) D. neither (a) nor (b)

Answer 91

C. both (a) & (b)

Question 92

In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is __________ the outlet temperature of the cold fluid. A. equal to B. more than C. less than D. either more or less than (depending

Answer 92

A. equal to

Question 93

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

Answer 93

B. heat exchanger

Question 94

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

Answer 94

D. Grashoff number

Question 95

Pick out the wrong statement: A. With change in temperature, the radiant energy emitted by a black body remains unchanged. B. Absorptivity of a body approaches unity in case of diffuse reflection. C. Absorptivity of a perfectly black body is u

Answer 95

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

Question 96

Planck’s distribution law is valid for __________ bodies. A. black B. white C. coloured D. all (a), (b) & (c)

Answer 96

C. coloured

Question 97

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

Answer 97

A. increased

Question 98

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

Answer 98

A. 0 K

Question 99

The interchange factor for radiation heat transfer from surface ‘x’ to surface ‘y’ in case of an infinite parallel planes with emis-sivities ?x & ?y is given by A. ?x + ?y B. ?x . ?y C. 1/?x + 1/?y D. (?x + ?y)/(?x + ?y - ?x . ?y)

Answer 99

D. (?x + ?y)/(?x + ?y - ?x . ?y)

Question 100

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

Answer 100

C. <1

Question 101

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

Answer 101

B. ha = 2hl

Question 102

jH factor for heat transfer is not a function of the __________ number. A. Reynolds B. Nusselt C. Grashoff D. both (b) & (c)

Answer 102

D. both (b) & (c)

Question 103

The Fourier number (defined as a.t/L2) is used in the analysis of problem involving heat transfer by A. forced convection B. natural convection C. transient conduction D. steady state conduction

Answer 103

C. transient conduction

Question 104

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

Answer 104

B. Q ? T^4

Question 105

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

Answer 105

C. heat transfer co-efficient

Question 106

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

Answer 106

C. 0.1

Question 107

In case of a vertical tube evaporator, with increase in the liquor level, the A. capacity of the evaporator is decreased. B. capacity of the evaporator is increased. C. true temperature drop increases. D. both (b) and (c).

Answer 107

A. capacity of the evaporator is decreased.

Question 108

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

Answer 108

C. temperature of the body

Question 109

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

Answer 109

A. decreases

Question 110

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

Answer 110

C. both counter and parallel-flow of the fluids.

Question 111

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

Answer 111

A. < 1

Question 112

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

Answer 112

B. decreases

Question 113

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

Answer 113

B. Sieder-Tate equation

Question 114

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

Answer 114

B. enhance turbulence.

Question 115

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

Answer 115

B. < 1

Question 116

LMTD correction factor which is to be applied for a cross-flow heat exchanger increases with increase in the number of shell passes. Its value for a single pass cross flow heat exchanger is A. 0 B. 1 C. >1 D. <1

Answer 116

D. <1

Question 117

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

Answer 117

C. Schmidt number

Question 118

Latent heat absorbed by 1 lb of water at 212 F, when it is changed to steam at 212 F, may be around __________ BTU. A. 180 B. 970 C. 3.97 D. none of these

Answer 118

A. 180

Question 119

In counter flow compared to parallel flow, A. LMTD is greater. B. less surface area is required for a given heat transfer rate. C. both (a) and (b). D. more surface area is required for a given heat transfer rate.

Answer 119

C. both (a) and (b).

Question 120

The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2. The approximate surface temperature (K) is (Stefan-Boltzman constant = 5.67xl0-8 W/m2.K4) A. 1000 B. 727 C. 800 D. 1200

Answer 120

A. 1000

Question 121

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

Answer 121

A. exothermic

Question 122

A multiple effect evaporator has a capacity to process 4000 kg of solid caustic soda per day, when it is concentrating from 10% to 25% solids. The water evaporated in kg per day is A. 6000 B. 24000 C. 60000 D. 48000

Answer 122

B. 24000

Question 123

Value of Prandtl number for water ranges from A. 1 to 2 B. 5 to 10 C. 100 to 500 D. 1000 to 2000

Answer 123

B. 5 to 10

Question 124

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

Answer 124

B. conduction

Question 125

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

Answer 125

C. partial ionisation

Question 126

Reynold’s analogy states that (where, St = Stanton number f = friction factor) A. St = f/2 B. St = f/4 C. St = 4f D. St = f^1/2

Answer 126

A. St = f/2

Question 127

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

Answer 127

B. backward

Question 128

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

Answer 128

B. 1

Question 129

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

Answer 129

A. cummulatively increases

Question 130

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

Answer 130

A. increases

Question 131

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

Answer 131

B. ? 1/t

Question 132

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

Answer 132

A. increasing temperature.

Question 133

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

Answer 133

C. transmits

Question 134

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

Answer 134

B. black & rough

Question 135

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

Answer 135

B. 1-1.3

Question 136

A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is A. 5.6 B. 0.025 C. 3.5 D. 0.0035

Answer 136

B. 0.025

Question 137

Analogy between mass and heat transfer is not applicable in case of A. same velocity profile or equal eddy diffusivities. B. thermal or pressure mass diffusion. C. viscous heating or chemical reaction. D. both (b) and (c).

Answer 137

D. both (b) and (c).

Question 138

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

Answer 138

B. black & rough

Question 139

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

Answer 139

C. d^2

Question 140

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

Answer 140

B. distilled water

Question 141

A measure of the extent to which viscous heating is important relative to the heat flow resulting from the impressed temperature difference is represented by the __________ number. A. Condensation B. Grashoff C. Stantan D. Brinkman

Answer 141

D. Brinkman

Question 142

Out of 100 kcal/second of incident radiant energy on the surface of a thermally transparent body, 300 kcal/second is reflected back. If the transmissivity of the body is 0.25, the emissivity of the surface will be A. 0.35 B. 0.45 C. 0.55 D

Answer 142

B. 0.45

Question 143

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

Answer 143

D. arrest the entrained liquid

Question 144

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

Answer 144

A. zero

Question 145

Fouling factor’ used in the design of a multipass shell and tube heat exchanger is a A. non-dimensional factor. B. factor of safety. C. conversion factor for individual film heat transfer co-efficient to overall heat transfer co-efficient.

Answer 145

B. factor of safety.

Question 146

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

Answer 146

B. d^-0.2

Question 147

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

Answer 147

B. 1

Question 148

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

Answer 148

B. density

Question 149

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

Answer 149

B. Prandtl

Question 150

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

Answer 150

B. r = k/h

Question 151

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the A. temperature of the body only. B. wavelength of monochromatic radiation. C. both (a) and (b). D. nature of material of body.

Answer 151

A. temperature of the body only.

Question 152

If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid A. remains unchanged. B. increases. C. increases or decreases depending on number of shell passes. D. decreases.

Answer 152

D. decreases.

Question 153

The heat transfer by radiation from a mild steel surface is to be reduced by reducing the emissivity of the surface. This can be best achieved by A. painting the surface black. B. painting the surface white (with aluminium paint). C. giving th

Answer 153

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

Question 154

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

Answer 154

A. Black

Question 155

What is Nusselt number? A. (Cp ?)/k B. hD/k C. (h Cp)/? D. (Cp ?)/h

Answer 155

B. hD/k

Question 156

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

Answer 156

C. remove condensate and inert gases.

Question 157

The Dietus-Boelter equation for convective leat transfer
https://www.indiabix.com/_files/images/chemical-engineering/heat-transfer/245-165-1.png
cannot be used for (See picture for equation) A. low Reynold’s number B. very low Grashoff number

Answer 157

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

Question 158

A hot liquid is kept in a big room. The logorithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly a/an A. ellipse B. straight line C. parabola D. ci

Answer 158

B. straight line

Question 159

Radiation heat transfer rates does not depend upon the A. type of absorbing surface. B. distance between the heat source and the object receiving the heat. C. surface area and temperature of the heat source. D. none of these.

Answer 159

D. none of these.

Question 160

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

Answer 160

B. Driving force = Rate x Resistance

Question 161

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

Answer 161

B. Newton’s law of cooling

Question 162

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

Answer 162

C. goes through a minimum.

Question 163

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

Answer 163

B. heat flux

Question 164

Log mean temperature difference (LMTD) cannot be used, if A. heat transfer co-efficient over the entire heat exchanger is not constant. B. there exists an unsteady state. C. the heat capacity is not constant and there is a phase change. D.

Answer 164

D. none of these.

Question 165

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

Answer 165

B. four times

Question 166

For a given ambient air temperature with increase in the thickness of insulation of a hot cylinderical pipe, the rate of heat loss from the surface would A. decrease B. increase C. first decrease and then increase D. first increase and the

Answer 166

D. first increase and then decrease

Question 167

In a parallel flow heat exchanger, if the outlet temperature of hot and cold fluids are the same, then the log mean temperature difference (LMTD) is A. minimum B. maximum C. zero D. infinity

Answer 167

C. zero

Question 168

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

Answer 168

B. 0.6 to 120

Question 169

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

Answer 169

B. least at the outlet of the last effect.

Question 170

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

Answer 170

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

Question 171

For the same heat transfer area and the terminal conditions, the ratio of the capacities of a single effect evaporator to a triple effect evaporator is A. 3 B. 0.33 C. 1 D. 1.33

Answer 171

C. 1

Question 172

The variation of thermal conductivity of a metal with temperature is often correlated using an expression of the form K = K0 + at. where, K is the thermal conductivity and T is the temperature (in K). The units of ‘a’ in SI system will be A. W/m.k

Answer 172

C. W/m.k2

Question 173

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

Answer 173

C. clean & smooth

Question 174

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

Answer 174

A. Prandtl number

Question 175

If Prandtl number is greater than the Schmidt number, then the A. thermal boundary layer lies inside the concentration boundary layer. B. concentration boundary layer lies inside the thermal boundary layer. C. thermal & concentration boundary

Answer 175

A. thermal boundary layer lies inside the concentration boundary layer.

Question 176

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

Answer 176

C. Catchall

Question 177

Rate of heat transfer by vaporisation from pools of water is affected by the A. nature of heating surface and distribution of bubbles. B. surface tension of water. C. viscosity of water. D. all (a), (b) and (c).

Answer 177

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

Question 178

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

Answer 178

C. P and S

Question 179

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

Answer 179

D. Silver

Question 180

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

Answer 180

C. Grashoff number

Question 181

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

Answer 181

B. vertical heat exchanger with steam on shell side.

Question 182

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

Answer 182

A. reduce the capacity

Question 183

The rate of heat transfer through a pipe wall is given by, https://www.indiabix.com/_files/images/chemical-engineering/heat-transfer/271-499-1.png . For cylinder of very thin wall, q can be approximated by A. https://www.indiabix.com/_files/images/che

Answer 183

D. https://www.indiabix.com/_files/images/chemical-engineering/heat-transfer/271-499-5.png

Question 184

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

Answer 184

C. contaminated cooling

Question 185

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

Answer 185

B. cross-sectional area

Question 186

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

Answer 186

A. Swenson-Walker crystalliser is a batch crystalliser.

Question 187

In case of a vertical tube evaporator, with increase in the liquor level, the __________ is increased. A. velocity of circulation B. liquor-film co-efficient C. both (a) and (b) D. neither (a) and (b)

Answer 187

D. neither (a) and (b)

Question 188

Electromagnetic radiations propagate in vacuum with a velocity of __________ metre/second. A. 3 x l05 B. 3 x l08 C. 3 x l010 D. 3 x l012

Answer 188

B. 3 x l08

Question 189

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

Answer 189

B. area

Question 190

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

Answer 190

D. very high

Question 191

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

Answer 191

C. resistances in series.

Question 192

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

Answer 192

D. constant temperature equal to that of the base

Question 193

Vacuum is generally maintained in the vapour space of an evaporator mainly to A. get economical temperature difference by using moderate pressure steam. B. facilitate forward feeding in multiple effect evaporation. C. concentrate heat sensitiv

Answer 193

A. get economical temperature difference by using moderate pressure steam.

Question 194

Double pipe heat exchangers are used A. when heat transfer area required is very high. B. when heat transfer area required is very low, i.e (100-200 ft2). C. because it occupies less floor area. D. because it is less costly.

Answer 194

B. when heat transfer area required is very low, i.e (100-200 ft2).

Question 195

Nusselt number (for forced convection heat transfer) is a function of the __________ number. A. Prandtl B. Reynolds C. both (a) & (b) D. neither (a) nor (b)

Answer 195

C. both (a) & (b)

Question 196

Pick out the wrong statement. A. Heat transfer by radiation can not occur across an absolute volume. B. In case of a shell and tube heat exchanger, the pressure drop through the shell is proportional to the number of times the fluid crosses the bu

Answer 196

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

Question 197

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

Answer 197

C. Series and parallel set of shell and tube

Question 198

Pick out the wrong statement. A. Reciprocal of the resistance to heat flow is called thermal conductance. B. Unit of thermal conductance is W/ K. C. Thermal conductance of a wall of thickness ‘L’, thermal conductivity ‘k’ and heat flow area ‘A

Answer 198

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

Question 199

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

Answer 199

D. between 0 and 1

Question 200

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

Answer 200

B. buoyancy to viscous forces.

Question 201

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

Answer 201

C. f/2

Question 202

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

Answer 202

C. under thermal equilibrium.

Question 203

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

Answer 203

A. 1 and 0

Question 204

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

Answer 204

D. ? = 1; ? = 1

Question 205

Pick out the wrong statement. A. Superheated steam is preferably not used for process heating because of its low heat transfer film co-efficient. B. In a shell and tube heat exchanger, the shell pressure drop is maximum for orifice baffles. C.

Answer 205

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

Question 206

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

Answer 206

B. convection

Question 207

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

Answer 207

C. Sphere

Question 208

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

Answer 208

A. remove non-condensable gases.

Question 209

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

Answer 209

B. high co-efficient of thermal expansion.

Question 210

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

Answer 210

B. pool

Question 211

A body cools down from 75 C to 70 C in 10 minutes. It will cool down from 70 C to 65 C in __________ minutes. A. 10 B. >10 C. <10 D. either (b) or (c), depends on the mass of the body

Answer 211

B. >10

Question 212

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

Answer 212

A. Re and Pr

Question 213

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

Answer 213

B. 1

Question 214

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 evap

Answer 214

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

Question 215

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

Answer 215

A. keeping the heat transfer surface clean.

Question 216

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

Answer 216

B. condensate

Question 217

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 1

Answer 217

D. 160

Question 218

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

Answer 218

A. sum

Question 219

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

Answer 219

A. decreases

Question 220

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

Answer 220

B. less

Question 221

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

Answer 221

A. Grashoff number

Question 222

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

Answer 222

B. 4.364

Question 223

Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary layer, when the value of Prandtl number is A. 1 B. < 1 C. > 1 D. > 5

Answer 223

B. < 1

Question 224

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

Answer 224

A. K/h0

Question 225

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

Answer 225

C. (?T)^3

Question 226

In a 1-1 cocurrent heat exchanger, if the tube side fluid outlet temperature is equal to the shell side fluid outlet temperature, then the LMTD is A. ? B. 0 C. equal to the difference between hot and cold fluids inlet temperature. D. equal

Answer 226

B. 0

Question 227

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

Answer 227

C. same for all wavelengths

Question 228

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

Answer 228

B. flows outside the tubes.

Question 229

In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the entrance of the tube is A. infinity. B. zero. C. same as average heat transfer co-efficient for tube side. D. none of these.

Answer 229

A. infinity.

Question 230

Grashoff number, which is defined as g . ?(Ts - T?) ?2. L3/?2, is proportional to the ratio of buoyancy force to __________ force. A. viscous B. elastic C. inertial D. none of these.

Answer 230

A. viscous

Question 231

Pick out the wrong statement. A. By increasing the number of shell passes, the temperature cross in a shell and tube heat exchanger can be prevented. B. An underdesigned steam trap will back up the condensate instead of discharging it out. C.

Answer 231

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

Question 232

Graetz number is given by A. mCp/kL B. kL/mCp C. mCp/k? D. kL/mCp

Answer 232

A. mCp/kL

Question 233

For a cold dilute feed to produce thick viscous liquor, backward feeding as compared to forward feeding results in A. increased economy B. decreased economy C. lower capacity D. no effect on economy

Answer 233

A. increased economy

Question 234

Economy of an evaporator is influenced by the A. steam pressure B. feed temperature C. number of effect D. both(b) & (c)

Answer 234

D. both(b) & (c)

Question 235

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

Answer 235

C. linear

Question 236

In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred A. through a metallic wall. B. by direct contact of hot flue gas with air. C. by heating an intermediate material (like chequor bricks) and then hea

Answer 236

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

Question 237

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

Answer 237

C. Lee’s

Question 238

For small temperature difference, the heat transfer rate as per Newton’s law of cooling is proportional to (where, ?t = excess temperature) A. ?t B. ?t^2 C. ?t^3 D. sqrt?t

Answer 238

A. ?t

Question 239

Pick out the wrong statement. A. The condensing film co-efficient is about 3 times lower for vertical condenser as compared to the equivalent horizontal condenser for identical situation. B. Film co-efficient for vaporisation decreases as a result

Answer 239

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

Question 240

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

Answer 240

C. agitated film

Question 241

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

Answer 241

A. 1.49

Question 242

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

Answer 242

D. none of these

Question 243

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

Answer 243

A. Prandtl

Question 244

For a perfectly transparent surface (like gases), the A. B. transmissivity = 1 C. reflectivity = 0 D. all (a), (b) & (c)

Answer 244

B. transmissivity = 1

Question 245

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

Answer 245

B. different

Question 246

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

Answer 246

B. supersaturated

Question 247

An evaporator while concentrating an aqueous solution from 10 to 40% solids evaporates 30000 kg of water. The amount of solids handled by the system in kg is A. 4000 B. 9000 C. 4600 D. 3000

Answer 247

A. 4000

Question 248

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

Answer 248

A. low thermal conductivity.

Question 249

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

Answer 249

B. feed flows from low pressure to high pressure.

Question 250

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

Answer 250

B. Nu = (Re) (Pr) (St)

Question 251

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

Answer 251

D. none of these.

Question 252

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

Answer 252

C. parabolic

Question 253

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

Answer 253

B. logarithmic

Question 254

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

Answer 254

B. there is no risk of contamination.

Question 255

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

Answer 255

A. abundance & high heat capacity

Question 256

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

Answer 256

D. shape and porosity of the body.

Question 257

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

Answer 257

A. Steel

Question 258

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

Answer 258

B. turbulent

Question 259

In case of __________ boiling, the liquid temperature is below the saturation temperature and the boiling takes place in the vicinity of the heated surface. A. nucleate B. local C. pool D. saturated

Answer 259

B. local

Question 260

The ratio of velocity head to tube side return loss in case of a multipass shell and tube heat exchanger is A. 2 B. 45293 C. 4 D. 45295

Answer 260

D. 45295

Question 261

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

Answer 261

A. approach

Question 262

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

Answer 262

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

Question 263

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

Answer 263

A. a higher capacity

Question 264

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 i

Answer 264

C. 81.25

Question 265

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

Answer 265

A. U1 = U2

Question 266

In SI units, thermal conductivity is expressed in A. Watt/m. K B. Watt/m2. K C. Watt/m2. K D. Watt/m4. K

Answer 266

A. Watt/m. K

Question 267

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

Answer 267

A. boiling point (at the same pressure)

Question 268

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

Answer 268

D. sum

Question 269

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

Answer 269

C. > 0.6

Question 270

A sphere of radius ‘R1’ is enclosed in a sphere of radius ‘R2’. The view (or shape) factor for radiative heat transfer of the outer sphere with respect to the inner sphere is A. 0 B. R2/(R1+R2) C. 1 D. (R1/R2)^2

Answer 270

B. R2/(R1+R2)

Question 271

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.

Answer 271

B. 0.794 h1

Question 272

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

Answer 272

C. heat transfer area.

Question 273

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

Answer 273

B. 4.88 kcal/hr. m.2 C.

Question 274

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

Answer 274

A. Molten sodium (a coolant used in fast breeder reactor)

Question 275

In SI units, fouling factor is expressed in A. m2 K/W B. W/m2 K C. m2 K D. m K/W

Answer 275

A. m2 K/W

Question 276

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

Answer 276

D. none of these

Question 277

Extremely large or small volumes of fluids are generally best routed through the shell side of a shell and tube heat exchanger, because of the A. less corrosion problems. B. flexibility possible in the baffle arrangement. C. low pressure drop.

Answer 277

B. flexibility possible in the baffle arrangement.

Question 278

All analogy equations connecting friction factor and heat transfer co-efficient apply only to A. wall or skin friction B. form friction C. both (a) and (b) D. turbulent flow

Answer 278

A. wall or skin friction

Question 279

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

Answer 279

B. 0.5 to 50

Question 280

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

Answer 280

D. Nu, Gz

Question 281

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

Answer 281

B. thickness

Question 282

A black body does not __________ radiation. A. absorb or emit B. refract C. reflect D. both(b) & (c)

Answer 282

D. both(b) & (c)

Question 283

The capacity of double-effect evaporator is less than half of the capacity of two single effects, each of which is operating over same terminal temperature difference, when the A. solution has an elevation of boiling point. B. evaporators operate

Answer 283

A. solution has an elevation of boiling point.

Question 284

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

Answer 284

A. Pe = Re.Pr

Question 285

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

Answer 285

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

Question 286

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

Answer 286

B. momentum diffusivity to thermal diffusivity.

Question 287

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

Answer 287

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

Question 288

Forced circulation evaporators are useful for the concentration of viscous, salting and scale forming liquors. Which of the following is a forced circulation evaporator? A. Long vertical evaporator B. Horizontal tube evaporator C. Agitated fil

Answer 288

C. Agitated film evaporator

Question 289

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

Answer 289

A. Kirchoffs

Question 290

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

Answer 290

D. radiation

Question 291

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

Answer 291

C. higher tube side heat transfer co-efficient.

Question 292

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

Answer 292

C. < 1

Question 293

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

Answer 293

D. none of these

Question 294

Pick out the wrong statement. A. Fluid movement under the influence of buoyant forces resulting from change in density takes place in case of natural convection. B. The ratio NNu/NRe . Npr is called the Stanton number. C. The Peclet number is

Answer 294

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

Question 295

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

Answer 295

B. U-tube

Question 296

Pick out the wrong statement. A. In drying a solid containing moisture above the critical moisture content the number of degrees of freedom is 2. B. Sherwood number in mass transfer corresponds to Nusselt number in heat transfer and Schmidt number

Answer 296

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

Question 297

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

Answer 297

B. viscous

Question 298

The thickness of condensate layer in filmwise condensation depends on the A. condensation rate B. surface configuration C. liquid flow rate from the surface D. all (a), (b) and (c)

Answer 298

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

Question 299

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

Answer 299

A. parabolic

Question 300

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

Answer 300

A. basket type

Question 301

Harmonic mean temperature difference is given by A. sqrt(?T1. ?T2) B. (2. ?T1. ?T2)/(?T1 + ?T2) C. (2. ?T1. ?T2)/(?T1 - ?T2) D. ( ?T1 - ?T2)/(?T1 . ?T2)

Answer 301

B. (2. ?T1. ?T2)/(?T1 + ?T2)

Question 302

Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is A. thin walled having the value of Ao Ai/< 2. B. thick walled. C. having the value of Ao/Ai > 2. D. both (b) and

Answer 302

A. thin walled having the value of Ao Ai/< 2.

Question 303

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 event

Answer 303

A. cube

Question 304

Overall heat transfer co-efficient for cooling of hydrocarbons by water is about A. 50 -100 Kcal/hr.m2. C B. 50 -100 W/m2 . K C. 50 -100 BTU/hr. ft.2 F D. 1000 - 1500 BTU/hr. ft.2 F

Answer 304

C. 50 -100 BTU/hr. ft.2 F

Question 305

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

Answer 305

D. coke breeze

Question 306

Thermal diffusivity is given by A. k/p.Cp B. p.Cp/k C. Cp.?/a D. ?/hCp

Answer 306

A. k/p.Cp

Question 307

At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a fluid flowing over a heated plate will be identical? A. 1 B. < 1 C. > 1 D. none of these

Answer 307

A. 1

Question 308

Fourier’s law of heat conduction applies to __________ surfaces. A. isothermal B. non-isothermal C. both (a) and (b) D. neither (a) and (b)

Answer 308

C. both (a) and (b)

Question 309

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

Answer 309

A. Dirhing’s

Question 310

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

Answer 310

D. Temperature difference between the two surfaces of the wall.

Question 311

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

Answer 311

A. Nitrogen

Question 312

In a heat exchanger, one transfer unit means A. a section of the exchanger in which change in temperature of one stream equals the average driving force in the section. B. the size of the exchanger in which heat transfer rate is 1 kcal/hr. C.

Answer 312

A. a section of the exchanger in which change in temperature of one stream equals the average driving force in the section.

Question 313

For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise condensation are respectively hf and hd, then A. hf = hd B. hf > hd C. hf < hd D. hf could be greater or smaller than hd

Answer 313

C. hf < hd

Question 314

Pick out the wrong statement: A. The capacity of an evaporator is reduced by the boiling point elevation. B. Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger. C. Steam jet ejector is used for vapor compr

Answer 314

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

Question 315

For concentrating an aqueous solution of a material like anhydrous Na2SO4, whose solubility decreases with rise in temperature, the most suitable evaporator is a __________ evaporator. A. high pressure B. vacuum C. backward feed D. none of

Answer 315

B. vacuum

Question 316

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

Answer 316

C. create more suction head.

Question 317

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

Answer 317

C. Wien’s displacement

Question 318

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

Answer 318

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

Question 319

At steady state the temperature variation in a plane wall, made of two different solids I & II is shown below :

The thermal conductivity of material I A. is smaller than that of II. B. is greater than that of II. C. is equal to that of II.

Answer 319

A. is smaller than that of II.

Question 320

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

Answer 320

C. evaporation

Question 321

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

Answer 321

B. 0.75 D

Question 322

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

Answer 322

A. large scale evaporation of liquor is needed

Question 323

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. 2^0.8 B. 4^0.8 C. 4^0.4

Answer 323

B. 4^0.8

Question 324

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

Answer 324

B. U-tube

Question 325

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

Answer 325

A. Transient heat conduction

Question 326

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

Answer 326

B. White lead

Question 327

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. Gra

Answer 327

C. exit fluid temperature = wall temperature.

Question 328

1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is A. 520 B. 200 C. 400 D. 500

Answer 328

C. 400

Question 329

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

Answer 329

A. Open pan evaporation

Question 330

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

Answer 330

B. temperature distribution is dependent on time.

Question 331

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

Answer 331

A. 1

Question 332

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

Answer 332

C. forced convection

Question 333

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

Answer 333

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

Question 334

Boiling point elevation of a solution of NaOH A. increases rapidly with temperature rise. B. is almost independent of temperature. C. is almost independent of pressure. D. both (b) and (c).

Answer 334

D. both (b) and (c).

Question 335

The advantage of backward feed multiple effect evaporators over forward feed units is that A. heat sensitive material can be handled. B. there is no additional cost of pumping. C. most concentrated liquid is at highest temperature. D. equa

Answer 335

C. most concentrated liquid is at highest temperature.

Question 336

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

Answer 336

D. Interfacial tension

Question 337

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

Answer 337

D. None of these

Question 338

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

Answer 338

B. decreases

Question 339

A metal ball of radius 0.1 m at a uniform temperature of 90 C is left in air at 30 C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradie

Answer 339

D. 0.15

Question 340

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

Answer 340

A. avoid buckling of tubes.

Question 341

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

Answer 341

D. 51 min

Question 342

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

Answer 342

B. sum of all resistances.

Question 343

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

Answer 343

B. requirement of heat transfer area is low.

Question 344

Removal of __________ heat is involved in the condensation of a vapor under saturated conditions. A. super B. sensible C. latent D. both(b) & (c)

Answer 344

C. latent

Question 345

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (?T) between wall and outside bulk. The proportionality is given as A. (?T)^1/4 B. (?T)^1/2 C. (?T)^5/4 D. (?T)^3/4

Answer 345

D. (?T)^3/4

Question 346

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

Answer 346

B. decrease

Question 347

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

Answer 347

C. 1

Question 348

The outlet temperature of cooling water in a heat exchanger is generally not allowed to exceed above 50 C in industrial practice mainly to avoid A. its evaporation loss B. excessive corrosion C. uneconomic LMTD D. decrease in heat exchange

Answer 348

B. excessive corrosion

Question 349

In evaporators, lowering the feed temperature A. increases the heating area required. B. reduces the economy. C. both (a) and (b). D. decreases the heating area required.

Answer 349

C. both (a) and (b).

Question 350

The type of liquor circulation system to be ‘ employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid. A. viscosity B. density C. thermal conductivity D. corrosive nature

Answer 350

A. viscosity

Question 351

In case of surface condensers, a straight line is obtained on plotting __________ on an ordinary graph paper. A. 1/ v^-0.8 B. v^-0.8 C. v^-2 D. 1/ v^-2

Answer 351

A. 1/ v^-0.8

Question 352

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

Answer 352

A. conduction

Question 353

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

Answer 353

B. Reyleigh

Question 354

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

Answer 354

C. partial condenser

Question 355

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

Answer 355

C. Black paint

Question 356

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

Answer 356

B. entrainment separator

Question 357

Fouling factor for a heat exchanger is given by (where, U1 = heat transfer co-efficient of dirty surface U2 = heat transfer co-efficient of clean surface) A. U1 - U2 B. 1/U1 - 1/U2 C. 1/U2 - 1/U1 D. U2 - U1

Answer 357

B. 1/U1 - 1/U2

Question 358

If a single tube pass heat exchanger is converted to two pass, then for the same flow rate, the pressure drop per unit length in tube side will A. increase by 1.8 times B. decrease by 2^2 C. increase by 2^16 D. remain unchanged

Answer 358

C. increase by 2^16

Question 359

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 condition

Answer 359

A. 5 minutes

Question 360

Fluid motion in the natural convection heat transfer between a solid surface and a fluid in contact with it, results from the A. existence of thermal boundary layer. B. temperature gradient produced due to density difference C. buoyancy of the

Answer 360

D. none of these.

Question 361

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

Answer 361

B. vertical

Question 362

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

Answer 362

B. d^2T/dZ^2 = 0

Question 363

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

Answer 363

D. burnout

Question 364

Pick out the wrong statement. A. Heat transfer from a hot body to cold body by the emission of heat waves is called radiation: B. Filmwise condensation takes place on non-wettable surfaces. C. The boiling point of a solution is affected by liq

Answer 364

B. Filmwise condensation takes place on non-wettable surfaces.

Question 365

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

Answer 365

A. Nusselt

Question 366

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

Answer 366

B. momentum diffusivity to thermal diffusivity

Question 367

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

Answer 367

B. KA/x

Question 368

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

Answer 368

A. current

Question 369

The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body) A. ?T B. ? 1/T C. ? T^4 D. independent of T

Answer 369

B. ? 1/T

Question 370

In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat exchanger. A. once B. twice C. thrice D. four times

Answer 370

B. twice

Question 371

When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is A. free convection B. entry length problem in laminar forced conduction (developing thermal boundary layer) C. mixed

Answer 371

C. mixed convection (both free and forced)

Question 372

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

Answer 372

C. facilitate removal of non-condensable gases

Question 373

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

Answer 373

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

Question 374

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

Answer 374

C. higher steam economy

Question 375

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

Answer 375

B. Backward feed

Question 376

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

Answer 376

B. oily

Question 377

At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the A. buffer zone B. turbulent core C. both (a) and (b) D. viscous sub-layer

Answer 377

D. viscous sub-layer

Question 378

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

Answer 378

A. increases

Question 379

(NRe.NPr)(D/L)is called the __________ number A. Peclet B. Stanton C. Graetz D. none of these

Answer 379

C. Graetz

Question 380

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

Answer 380

B. on rough surfaces

Question 381

In forced circulation, the heating element is injected A. internally B. externally C. both (a) and (a) D. neither (a) nor (b)

Answer 381

A. internally

Question 382

If all the conditions and dimensions are same, then the ratio of velocity through the tubes of a double pass heat exchanger to that through the single pass heat exchanger is A. 1 B. 2 C. 45293 D. 4

Answer 382

B. 2

Question 383

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

Answer 383

B. Reynolds

Question 384

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 vi

Answer 384

A. boiling point

Question 385

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

Answer 385

D. none of these.

Question 386

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

Answer 386

B. Planck’s

Question 387

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

Answer 387

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

Question 388

A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case, A. the cooling rate will be the same for the two spheres and hence the two spheres will have equal temperatures at any instant.

Answer 388

D. both(b) & (c).

Question 389

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

Answer 389

B. condensate is corrosive in nature.

Question 390

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

Answer 390

A. At high fluid velocity

Question 391

The Sieder-Tate correlation for heat transfer in turbulent flow in pipe gives Nu ? Re^0.8, 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 pip

Answer 391

B. (D)^-0.2

Question 392

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

Answer 392

D. t = 800 s

Question 393

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

Answer 393

D. same in either ‘a’, b’ or ‘c’

Question 394

Thermal diffusivity of a material A. has the unit m2 /sec. B. is defined as K/? . Cp. C. is the ratio of thermal conductivity to thermal capacity. D. all (a), (b) and (c).

Answer 394

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

Question 395

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

Answer 395

B. increase slowly

Question 396

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

Answer 396

A. 1

Question 397

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

Answer 397

B. horizontal tube

Question 398

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

Answer 398

A. an oily surface.

Question 399

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

Answer 399

A. 0.1

Question 400

In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid A. varies directly as the area and the LMTD. B. directly proportional to LMTD and inversely proportional to the area. C. varies as square of the area. D. n

Answer 400

A. varies directly as the area and the LMTD.

Question 401

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

Answer 401

A. increases

Question 402

Loss of heat from untagged steam pipe to the ambient air is by A. conduction B. convection C. radiation D. all (a), (b) & (c)

Answer 402

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

Question 403

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

Answer 403

B. falling film

Question 404

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

Answer 404

A. both the tube sheets fixed.

Question 405

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. 2^0.8 C. 2^0.2 D. 2^0.5

Answer 405

B. 2^0.8

Question 406

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

Answer 406

A. vacuum

Question 407

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

Answer 407

B. more space.

Question 408

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

Answer 408

A. large temperature differentials.

Question 409

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

Answer 409

B. remove water resulting from partial condensation of steam.

Question 410

The average heat transfer co-efficient over the entire length of the plate (ha) and the local heat transfer co-efficient (hL), in case of heat transfer over a flat plate in lminar zone is related as A. ha = 0.8hL B. ha = 2hL C. ha = hL D.

Answer 410

B. ha = 2hL

Question 411

What is the logarithmic mean of r1 and r2 ? A. (r1-r2/ln(r1/r2)) B. (r1-r2/ln(r2/r1)) C. (r2-r1/ln(r1/r2)) D. (r1-r2/-ln(r1/r2))

Answer 411

A. (r1-r2/ln(r1/r2))

Question 412

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

Answer 412

C. turbulent

Question 413

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

Answer 413

C. Wien’s

Question 414

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 tempera

Answer 414

C. 70

Question 415

Which of the following parameters of the fluid is not very important, while deciding its route in a shell and tube heat exchanger? A. Corrosiveness & fouling characteristics B. pressure C. viscosity D. density

Answer 415

D. density

Question 416

Corrosiveness of steam condensate is due to the presence of A. CO2 B. dissolved O2 C. both (a) & (b) D. neither (a) nor (b)

Answer 416

C. both (a) & (b)

Question 417

The equation, (NSt x N2/3Pr) = f/2, is the __________ analogy. A. Colburn B. Reynolds C. Prandtl D. none of these.

Answer 417

A. Colburn

Question 418

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

Answer 418

C. super-saturation

Question 419

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

Answer 419

C. Reynolds

Question 420

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

Answer 420

A. capacity

Question 421

Pick out the correct statement. A. 1 kcal/hr.m. C is equal to 1 BTU/hr. ft. F. B. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity. C. In unsteady st

Answer 421

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

Question 422

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

Answer 422

B. highly viscous

Question 423

Cp.?/K is termed as the __________ number. A. Grashoff B. Nusselt C. Prandtl D. Stanton

Answer 423

C. Prandtl

Question 424

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

Answer 424

B. saturated

Question 425

Kirchoff’s law is applicable to A. monochromatic radiation only B. total radiation only C. both (a) and (b) D. only volumes and not to surfaces

Answer 425

C. both (a) and (b)

Question 426

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

Answer 426

B. lowest in last effect

Question 427

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. decrease C. remain uncha

Answer 427

C. remain unchanged

Question 428

Which of the following situations can be approximated to a steady state heat transfer system? A. A red hot steel slab (having outside surface temperature as 1300 C) exposed to the atmosheric air at 35 C. B. 10 kg of dry saturated steam at 8 kgf/cm

Answer 428

B. 10 kg of dry saturated steam at 8 kgf/cm2 flowing through a short length of stainless steel pipe exposed to atmospheric air at 35 C.

Question 429

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

Answer 429

A. 180

Question 430

The unit of conductance in SI unit is A. W/m B. W/m2 C. W/ K D. W/m K

Answer 430

C. W/ K

Question 431

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

Answer 431

A. gives a higher shell side pressure drop.

Question 432

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

Answer 432

A. Iron

Question 433

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. Th

Answer 433

B. 12

Question 434

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

Answer 434

A. increasing temperature of the vapour.

Question 435

Critical value of the __________ number governs the transition from laminar to turbulent flow in free convection heat transfer. A. Grashoff B. Reynolds C. both ‘a’ & ‘b’ D. Prandtl & Grashoff

Answer 435

D. Prandtl & Grashoff

Question 436

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

Answer 436

B. is thinner than hydrodynamic boundary layer.

Question 437

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

Answer 437

C. ?t^5/4

Question 438

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

Answer 438

B. decreases

Question 439

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

Answer 439

D. 0.7

Question 440

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

Answer 440

C. that across the entire pipe

Question 441

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

Answer 441

D. none of these

Question 442

The units of resistance to heat transfer is A. J.m-2.K-1 B. J.m-1.K-1 C. W.m-2.K-1 D. W-1m2K

Answer 442

D. W-1m2K

Question 443

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

Answer 443

B. increases

Question 444

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

Answer 444

A. Grashoff

Question 445

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

Answer 445

B. Double pipe

Question 446

It is not recommended to use a 1-2 shell and tube heat exchanger for a particular heat duty, whenever the LMTD correction factor is A. > 0.75 B. < 0.75 C. < 0.50 D. < 0.25

Answer 446

B. < 0.75

Question 447

Pick out the wrong statement. A. Economy of a multiple effect evaporator is not influenced by the boiling point elevation. B. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature. C. D

Answer 447

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

Question 448

In sub-cooled boiling, A. temperature of the heating surface is less than the boiling point of the liquid. B. temperature of the heating surface is more than the boiling point of the liquid. C. bubbles from heating surface are absorbed by the

Answer 448

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

Question 449

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

Answer 449

A. increases.

Question 450

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

Answer 450

A. basket type

Question 451

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

Answer 451

B. 7

Question 452

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

Answer 452

C. Grashoff number

Question 453

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

Answer 453

A. film

Question 454

Pick out the wrong statement. A. In process heat exchangers, saturated steam is preferred over the superheated steam. B. The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of ?1. If the surface temperature is

Answer 454

B. The maximum is the emissive power of a surface at a temperature T1 occurs at a wavelength of ?1. If the surface temperature is halved, the maximum in the emissive power would occur at a wavelength of 0.5 ?1.

Question 455

Mode of heat transfer involved in the cooling of air cooled internal combustion engine is A. conduction B. natural convection C. forced convection D. none of these

Answer 455

B. natural convection

Question 456

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

Answer 456

C. material is anisotropic.

Question 457

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

Answer 457

D. 48.7

Question 458

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

Answer 458

B. tube diameter

Question 459

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

Answer 459

B. 1-1 heat exchanger

Question 460

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

Answer 460

D. > 10000

Question 461

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2 C. A. 10-50 B. 100-500 C. 1000-1500 D. 5000-15000

Answer 461

D. 5000-15000

Question 462

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

Answer 462

C. cross

Question 463

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

Answer 463

B. always between h1 and h2

Question 464

One kilogram of water at 0 C is changed to superheated steam of one atm pressure and 300 C. The major heat consumption in the process will be to A. heat the water from 0 C to 100 C. B. evaporate the water. C. to superheat the steam. D. da

Answer 464

B. evaporate the water.

Question 465

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

Answer 465

C. high

Question 466

The radiation heat flux from a heating element at a temperature of 800 C, in a furnace maintained at 300 C is 8 kW/m2. The flux, when the element temperature is increased to 1000 C for the same furnace temperature is A. 11.2 kW/m2 B. 12.0 kW/m2

Answer 466

D. 16.5 kW/m2

Question 467

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

Answer 467

B. results in making part of the heating surface inactive.

Question 468

In case of a shell and tube heat exchanger, the minimum and maximum baffle spacing is respectively (where, D = inside diameter of the shell) A. D/5 and D B. D/2 and 2 D C. D/4 and 2 D D. D and 2 D

Answer 468

A. D/5 and D

Question 469

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

Answer 469

C. logarithmic

Question 470

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

Answer 470

D. all ‘a’, ‘b’ & ‘c’

Question 471

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

Answer 471

B. Long tube vertical evaporator

Question 472

Boiling point elevation of an ideal solution A. increases rapidly with temperature rise. B. decreases rapidly with temperature rise C. in independent of pressure. D. both (b) and (c).

Answer 472

A. increases rapidly with temperature rise.

Question 473

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

Answer 473

B. heat transfer area

Question 474

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

Answer 474

D. Air

Question 475

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

Answer 475

A. Aluminum foil

Question 476

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

Answer 476

C. all

Question 477

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 plat

Answer 477

C. kA < 0.5kB

Question 478

Vibrations in the tubes of a shell and tube heat exchanger is induced due to the A. flow of fluid on the tube and shell sides. B. oscillations in the flow of shell/tube sides fluid. C. vibrations transmitted through piping and/or supports due

Answer 478

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

Question 479

Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is A. 0.2 B. 0.4 C. 0.6 D. 0.8

Answer 479

C. 0.6

Question 480

The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe whose surface temperature remains constant is A. 1.66 B. 88.86 C. 3.66 D. dependent on NRe only

Answer 480

C. 3.66

Question 481

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

Answer 481

D. none of these

Question 482

The critical radius of insulation for a spherical shell is (where, K = thermal conductivity of insulating material h0 = heat transfer coefficient at the outer surface) A. K/h0 B. 2K/h0 C. h0/K D. h0/2K

Answer 482

B. 2K/h0

Question 483

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

Answer 483

D. direct contact

Question 484

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

Answer 484

C. forced convection and conduction

Question 485

The value of Stefan-Boltazman constant in SI unit is A. 5.6697 x 10-8W/m2. K4 B. 0.1714 x 10-8W/m2. K4 C. 5.6697 x 10-8kcal/m2 . K4 D. 0.1714 x 10-8kcal/m2. K4

Answer 485

A. 5.6697 x 10-8W/m2. K4

Question 486

The unit of heat transfer co-efficient is A. BTU/hr. ft2 F B. BTU/hr. F. ft. C. BTU/hr. F D. BTU/hr. ft

Answer 486

A. BTU/hr. ft2 F

Question 487

For turbulent flow in a tube, the heat transfer co-efficient is obtained from the Dittus-Boelter correlation. If the tube diameter is halved and the flow rate is doubled, then the heat transfer co-efficient will change by a factor of A. 1 B. 1.74

Answer 487

C. 6.1

Question 488

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 b

Answer 488

A. 165.4

Question 489

Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is A. 0.5 B. 2 C. 10 D. 100

Answer 489

B. 2

Question 490

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

Answer 490

B. high proportion of air space

Question 491

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

Answer 491

B. oily

Question 492

In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of A. concentrations B. chemical potenti

Answer 492

A. concentrations

Question 493

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

Answer 493

B. 0.6 to 120

Question 494

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

Answer 494

A. jH = (St)(Pr)^2/3 = f/2

Question 495

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

Answer 495

B. increase the steam economy & the capacity.

Question 496

Prandtl number is given by A. (Cp ?)/a B. hD/k C. (Cp ?)/k D. ?/(h Cp)

Answer 496

C. (Cp ?)/k

Question 497

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

Answer 497

D. steam jacketed kettle

Question 498

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

Answer 498

C. lead

Question 499

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

Answer 499

A. decrease

Question 500

Reason for operating an evaporator in multiple effect is to secure A. increased steam economy. B. decreased steam consumption. C. both (a) and (b). D. increased capacity.

Answer 500

C. both (a) and (b).