2. 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
Correct : B. 0.45
3. If air (a non-condensing gas) is present in a condensing vapor stream, it will __________
the condensation rate of vapor.
Correct : B. Decrease
4. The most conducive surface for dropwise condensation to occur is the __________ surface.
Correct : B. Oily
5. For a perfectly transparent surface (like gases), the
Correct : B. Transmissivity = 1
6. Shell side pressure drop in a shell and tube heat exchanger does not depend upon the
Correct : D. None of these
7. 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
Correct : B. d-0.2
8. In evaporators, lowering the feed temperature
Correct : C. Both (A) and (B)
9. Heat transfer co-efficient (h) for a fluid flowing inside a clean pipe is given by h = 0.023 (K/D) (DVρ/µ) 0.8 (CP.µ/k) 0.4. This is valid for the value of NRe equal to
Correct : D. > 10000
10. In case of vertical tube evaporator, with increase in liquor level, the overall heat transfer
co-efficient
Correct : B. Decreases
11. The ratio of kinematic viscosity to thermal diffusivity is called the __________ number.
Correct : B. Prandtl
12. Intermittent tube cleaning is possible to be done in case of a __________ evaporator.
Correct : A. Basket type
13. Vibrations in the tubes of a shell and tube heat exchanger is induced due to the
Correct : D. All (A), (B) and (C)
14. Pick out the wrong statement.
Correct : A. Orifice baffles are never used in a shell and tube heat exchanger
15. What is the steam economy in case of a single effect evaporator system?
Correct : C. < 1
16. Overall heat transfer co-efficient for cooling of hydrocarbons by water is about
Correct : C. 50 -100 BTU/hr. ft.2°F
17. For turbulent flow in a tube, the heat transfer co-efficient is obtained from the DittusBoelter 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
Correct : C. 6.1
18. For small temperature difference, the heat transfer rate as per Newton's law of cooling is
proportional to (where, Δt = excess temperature)
Correct : A. Δt
19. Baffles in the shell side of a shell and tube heat exchanger
Correct : C. Increase the shell side heat transfer co-efficient
20. The ratio of total radiating power to the absorptivity of the body depends upon the
__________ as per Kirchoff‟s law.
Correct : C. Temperature of the body
21. __________ chart is known as transient heat conduction chart.
Correct : A. Dirhing's
22. Steam side heat transfer co-efficient in an evaporator is in the range of __________
kcal/hr.m2 °C.
Correct : D. 5000-15000
23. Controlling heat transfer film co-efficient is the one, which offers __________ resistance to
heat transfer.
Correct : C. The largest
24. The main function of baffles provided in a shell and tube heat exchanger is to
Correct : B. Enhance turbulence
25. Pick out the wrong statement:
Correct : D. Heat sensitive materials should be concentrated in high pressure evaporators
26. Boiling point elevation of an ideal solution
Correct : A. Increases rapidly with temperature rise
27. Which of the following is concerned with both heat and mass transfer?
Correct : A. Lewis relationship
28. The thermal radiative flux from a surface of emissivity = 0.4 is 22.68 kW/m2 . The approximate surface temperature (K) is
(Stefan-Boltzmann constant = 5.67 × 10-8 W/m2 .K4 )
Correct : A. 1000
29. Duhring‟s rule is important in solving problems on
Correct : C. Evaporation
30. Which is the most suitable for the concentration of foamy & frothy liquors?
Correct : B. Long tube vertical evaporator
31. Heat transfer by radiation between two bodies at T1 & T2 and in an ambient temperature
of Ta°C depends on
Correct : D. None of these
32. Air is best heated with steam in a heat exchanger of
Correct : C. Double pipe type with fin on air side
33. The film thickness for laminar film condensation on vertical surface __________ from top
to bottom.
Correct : A. Cumulatively increases
34. 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
Correct : B. 0.025
35. __________ paint has the minimum absorption co-efficient.
Correct : B. White lead
36. The value of Stefan-Boltzmann constant in SI unit is
Correct : A. 5.6697 × 10-8W/m2.°K4
37. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost
per unit heat transfer area
Correct : D. Passes through a maxima
38. What is the thermal conductivity of a perfect heat insulator?
Correct : A. Zero
39. Mode of heat transfer in which the fluid moves under the influence of changes in fluid
pressure produced by external work is called
Correct : C. Forced convection
40. The ratio of momentum diffusivity to thermal diffusivity is the __________ number.
Correct : A. Prandtl
41. Steam traps are provided in steam carrying pipelines to
Correct : C. Remove condensate and inert gases
42. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m2.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is
Correct : D. 0.15
43. Kirchoff‟s law applies to __________ radiation.
Correct : C. Both (A) & (B)
44. Heat transfer occurs by natural convection because change in temperature causes
difference in
Correct : B. Density
45. Log mean temperature difference (LMTD) cannot be used, if
Correct : D. None of these
46. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (ΔT) between wall and outside bulk. The proportionality is given as
Correct : D. (ΔT) 3/4
47. Pick out the wrong statement.
Correct : B. The equivalent diameter of heat transfer for a duct of square cross-section (having each side as'x') is equal to 4x
48. 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
Correct : B. ha = 2hl
49. 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
Correct : C. Zero
50. Harmonic mean temperature difference is given by
Correct : B. 2 (ΔT1 . ΔT2)/(ΔT1 + ΔT2)
51. Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing
in it, is
Correct : C. Mainly confined to a thin film of fluid near the surface
52. 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 × 10-3 kg/m2 .s. The initial moisture content of the solid is 0.2 kg moisture/kg dry solid. The interfacial area available for drying is 4 m2 /1000 kg of dry solid. The moisture content at the end of the drying period is (in kg moisture/kg dry solid).
Correct : C. 0.1
53. If Prandtl number is greater than the Schmidt number, then the
Correct : A. Thermal boundary layer lies inside the concentration boundary layer
54. Fourier's law of heat conduction applies to __________ surfaces.
Correct : C. Both (A) and (B)
55. Thermal diffusivity is the most important in heat transfer by
Correct : A. Conduction
56. Which of the following is generally considered as opaque surface towards radiations?
Correct : D. Both (B) and (C)
57. 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
Correct : D. < 1
58. Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer co-efficient for the cooling water, whether on shell side or tube side is the same. The best arrangement is
Correct : B. Vertical heat exchanger with steam on shell side
59. The statement that "maximum wavelength of radiation is inversely proportional to the
temperature" is __________ law.
Correct : C. Wien's displacement
60. The steam ejector is used to
Correct : B. Create vacuum
61. Among liquids, water has a comparatively high value of thermal conductivity, due to its
Correct : C. Partial ionisation
62. Heat flux is the time rate of heat transfer per unit
Correct : B. Area
63. In which mode of heat transfer, the Biot number is important?
Correct : A. Transient heat conduction
64. The actual temperature drop across the heating surface in an evaporator depends on the
Correct : D. All (A), (B) and (C)
65. A diathermanous substance __________ the thermal radiation completely.
Correct : C. Transmits
66. 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
Correct : D. Constant temperature equal to that of the base
67. Boiling point elevation of a solution of NaOH
Correct : D. Both (B) and (C)
68. Thermal conductivity of a conducting solid material depends upon its
Correct : C. Both (A) & (B)
69. Radiant energy received by a body is proportional to (where, d = the distance between the
object emitting radiation and that receiving it.)
Correct : C. d2
70. Pick out the wrong statement.
Correct : C. Thermal conductance of a wall of thickness 'L', thermal conductivity 'k' and heat flow area 'A' is kL/A
71. Overall thermal resistance for conductive heat transfer through a series of flat resistances
is equal to the
Correct : B. Sum of all resistances
72. When vaporisation takes place directly at the heating surface, it is called
Correct : B. Nucleate boiling
73. Prandtl and Reynolds analogy are same, when Prandtl number is
Correct : B. 1
74. As per Kirchoff‟s law, the ratio of the total radiating power to the absorptivity of a body depends on the
Correct : A. Temperature of the body only
75. Arithmetic mean area can be used in heat transfer problem to calculate the heat flow by conduction through a cylinder which is
Correct : A. Thin walled having the value of Ao Ai /< 2
76. Fourier's law applies to the heat transfer by
Correct : C. Conduction
77. jH factor for heat transfer is not a function of the __________ number.
Correct : D. Both (B) & (C)
78. 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
Correct : B. Painting the surface white (with aluminium paint)
79. In a heat exchanger, one transfer unit means
Correct : A. A section of the exchanger in which change in temperature of one stream equals the average driving force in the section
80. Heat produced when a steady state current, I passes through an electrical conductor having
resistance, 'R' is
Correct : B. I2R
81. A 2-4 heat exchanger involves
Correct : C. Both counter and parallel-flow of the fluids
82. In a multipass shell and tube heat exchanger, tube side return pressure loss is equal to
__________ the velocity head.
Correct : B. Four times
83. In a shell and tube heat exchanger, the height of 25 percent cut baffles is equal to
(where, D = inside diameter of shell).
Correct : C. 0.75 D
84. 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
Correct : C. 35°C
85. Latent heat absorbed by 1 lb of water at 212°F, when it is changed to steam at 212°F, may
be around __________ BTU.
Correct : A. 180
86. Dittus-Boelter equation cannot be used for molten metals mainly due to its very low
Correct : A. Prandtl number
87. Baffle spacing
Correct : C. Should be less than the inside diameter of the shell
88. Steam consumption in kg/hr in case of an evaporator is given by (where, C & E are
capacity the economy of the evaporator respectively).
Correct : A. C/E
89. The local surface conductance for laminar film condensation on vertical surface is
(where, t = film thickness)
Correct : B. ∝ 1/t
90. Which of the following is unimportant in forced convection?
Correct : C. Grashoff number
91. The purpose of floating head in a heat exchanger is to
Correct : A. Avoid buckling of tubes
92. 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.
Correct : D. Highly turbulent
93. Mechanical recompression evaporation is used in the production of
Correct : B. Distilled water
94. Pick out the wrong statement.
Correct : A. Swenson-Walker crystalliser is a batch crystalliser
95. 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
Correct : B. Excessive corrosion
96. The number of kg vaporised per kg of steam fed to the evaporator is defined as
Correct : C. Economy
97. Vacuum is generally maintained in the vapour space of an evaporator mainly to
Correct : A. Get economical temperature difference by using moderate pressure steam
98. Three solid objects of the same material and of equal mass-a sphere, a cylinder (length = diameter) and a cube are at 500°C initially. These are dropped in a quenching bath containing a large volume of cooling oil each attaining the bath temperature eventually. The time required for 90% change in temperature is the smallest for
Correct : A. Cube
99. With increase in porosity, the thermal conductivity of a solid substance
Correct : B. Decreases
100. Which of the following forced convection heat transfer equation accounts for the liquid
viscosity effect for viscous liquids?