Correct : B. In steady state heat conduction, the only property of the substance which determines the temperature distribution, is the thermal conductivity
2. Evaporation by thermo compression results in the
Correct : C. Both (A) and (B)
3. 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).
Correct : B. 1/U1 - 1/U2
4. Use of transverse baffles in a shell and tube heat exchanger is done to increase the
Correct : D. All (A), (B) and (C)
5. All analogy equations connecting friction factor and heat transfer co-efficient apply only to
Correct : A. Wall or skin friction
6. Which of the following situations can be approximated to a steady state heat transfer system?
Correct : 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
7. Reason for operating an evaporator in multiple effects is to secure
Correct : C. Both (A) and (B)
8. Heat transfer by __________ may not necessarily require the presence of a medium.
Correct : D. Radiation
9. Fluid motion in the natural convection heat transfer between a solid surface and a fluid in
contact with it, results from the
Correct : D. None of these
10. Nusselt number is the ratio of the
Correct : C. Heat flux at the wall to that across the entire pipe
11. Critical value of the __________ number governs the transition from laminar to turbulent
flow in free convection heat transfer.
Correct : D. Prandtl & Grashoff
12. Prandtl number is the reciprocal of
Correct : A. Thermal diffusivity/Momentum diffusivity
13. In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by
the hot fluid is __________ the outlet temperature of the cold fluid.
Correct : A. Equal to
14. For a multipass shell and tube heat exchanger, the LMTD correction factor is always
Correct : C. < 1
15. Evaporator tubes are generally
Correct : B. Vertical
16. Thermal conductivity of a gas at low density, __________ with increase in temperature.
Correct : B. Increases
17. Which of the following is the most widely used heat insulating material for pipelines
carrying steam?
Correct : D. 85% magnesia cement and glass wool
18. The interchange factor for radiation heat transfer from surface 'x' to surface 'y' in case of an infinite parallel planes with emissivities εx & εy is given by
Correct : D. (εx + εy)/( εx + εy - εx . εy)
19. 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.
Correct : A. Parabolic
20. With increase in temperature, the thermal conductivity of a gas
Correct : A. Increases
21. Grashoff number is given by
Correct : A. gD3.β.Δtρ2/μ2
22. Which area is used in case of heat flow by conduction through a cylinder?
Correct : A. Logarithmic mean area
23. Pick out the wrong statement.
Correct : B. Filmwise condensation takes place on non-wettable surfaces
24. Choose the correct equation.
Correct : B. Nu = (Re) (Pr) (St)
25. In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid
Correct : A. Varies directly as the area and the LMTD
26. Pick out the wrong statement.
Correct : C. Heat transfer co-efficient during nucleate boiling is not influenced by the agitation imparted
27. For what value of Prandtl number, St = f/2?
Correct : B. 1
28. The rate of emission of radiation by a body does not depend upon the
Correct : D. Shape and porosity of the body
29. Heat sensitive materials can be concentrated in an evaporator employing
Correct : A. Vacuum
30. In a cooling tower, water becomes cool by
Correct : A. Loosing sensible heat
31. Conductance is given by (where, x = thickness, A = heat flow area, K = thermal
conductivity.)
Correct : B. KA/x
32. 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 ?
Correct : B. Constant rate of fluid flow
33. LMTD can't be used as such without a correction factor for the
Correct : D. All (A) (B) and (C)
34. What is the logarithmic mean of r1 and r2?
Correct : A. (r1 - r2)/ln(r1/r2)
35. In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be
Correct : B. More than 45°C
36. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar
flow through a circular pipe, where the wall heat flux is constant, is
Correct : B. 4.36
37. Heat flux, as defined in heat flow is analogous to __________ in electricity flow.
Correct : A. Current
38. The overall resistance for heat transfer through a series of flat resistance, is the __________
of the resistances.
Correct : D. Sum
39. The driving potential for the crystal growth during crystallisation is the __________ of the
solution.
Correct : C. Super-saturation
40. Heat transfer co-efficient equation for forced convection, Nu = 0.023 Re 0.8. Prn, is not valid, if the value of
Correct : D. Reynolds number for the flow involved is < 2100
41. 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)
Correct : B. NPr 1/3
42. 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.
Correct : B. Twice
43. An ejector is used to
Correct : D. None of these
44. In a forward feed multiple effect evaporator, the pressure is
Correct : B. Lowest in last effect
45. In a laboratory test run, the rate of drying was found to be 0.5 x 10-3 kg/m2 .s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m2 /kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is
Correct : C. 5000
46. With increase in temperature, the thermal conductivity of most liquids
Correct : B. Decreases
47. Peclet number (Pe) is given by
Correct : A. Pe = Re.Pr
48. The film co-efficient between condensing vapour and metal wall increases with
Correct : A. Increasing temperature of the vapour
49. In Fourier's law, the proportionality constant is called the
Correct : C. Thermal conductivity
50. The non-dimensional temperature gradient in a liquid at the wall of a pipe is the
Correct : A. Heat flux
51. When the ratio of the Grashoff number and to the square of Reynolds number is one, the dominant mechanism of heat transfer is:
Correct : C. Mixed convection (both free and forced)
52. "The ratio of the total emissive power to the absorptivity for all bodies is same at ther-mal equilibrium". This is __________ law.
Correct : A. Kirchoff’s
53. The units of resistance to heat transfer is
Correct : D. W-1m2K
54. For a liquid in laminar flow through a very long tube, when the exit fluid temperature
approaches the wall temperature, the equation to be used is
Correct : C. Nu = (2/π) Gz
55. For hot feed, forward feeding as compared to backward feeding results in __________
economy.
Correct : A. Increased
56. Pick out the wrong statement.
Correct : D. The Colburn jH factor for heat transfer is given by Nst Npr
57. In sub-cooled boiling,
Correct : B. Temperature of the heating surface is more than the boiling point of the liquid
58. Which is the best tube arrangement (in a shell and tube heat exchanger) if the fluids are
clean and non-fouling?
Correct : B. Triangular pitch
59. Heat transfer by conduction results due to the transfer of free electrons, kinetic energy & vibrational energy from one molecule to another. Conduction heat transfer cannot take place
Correct : B. Between two bodies not in physical contact with each other
60. A multiple effect evaporator as compared to a single effect evaporator of the same capacity
has
Correct : C. Higher steam economy
61. The thickness of condensate layer in filmwise condensation depends on the
Correct : D. All (A), (B) and (C)
62. With increase in temperature, the total emissivity of conductors
Correct : A. Increases
63. Steam economy in case of a triple effect evaporator will be
Correct : C. > 1
64. Dittus-Boelter equation used for the determination of heat transfer co-efficient is valid
Correct : B. For fluids in turbulent flow
65. In a forward feed multiple effect evaporator unit
Correct : D. None of these
66. In a shell and tube heat exchanger, floating head is used for
Correct : A. Large temperature differentials
67. The heat transfer co-efficient in film type condensation is __________ that for dropwise
condensation.
Correct : B. Lower than
68. Resistance to heat flow by conduction is proportional to (where, t & ρ are thickness & density of the material respectively and A = area normal to the direction of heat flow.)
Correct : D. All (A), (B) & (C)
69. Dropwise condensation is promoted on a/an __________ surface.
Correct : B. Oily
70. Maximum heat transfer rate is obtained in __________ flow.
Correct : B. Turbulent
71. Which of the following parameters of the fluid is not very important, while deciding its route
in a shell and tube heat exchanger?
Correct : D. Density
72. In case of a super-cooled solution, which is on the verge of crystallisation, the free energy of the solution as compared to that of the solid is
Correct : A. More
73. It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is
Correct : A. 3.06 × 105
74. In a single evaporator system, the steam economy __________ by creating vacuum in the
evaporator.
77. The overall heat transfer co-efficient for a shell and tube heat exchanger for clean surfaces is U0 = 400 W/m2.K. The fouling factor after one year of operation is found to be hd0 = 2000W/m2.K. The overall heat transfer co-efficient at this time is
Correct : C. 333 W/m2.K
78. The Graetz number is concerned with the
Correct : D. Heat transfer in laminar flow
79. At what value of Prandtl number, conduction is negligible in the turbulent core of a fluid
flowing through a heated pipe?
Correct : C. > 0.6
80. The unit of conductance in SI unit is
Correct : C. W/°K
81. Pick out the wrong statement.
Correct : B. Thermal conductivity of a dry material is more than that of the damp material
82. Pick out the correct statement.
Correct : B. Logarithmic mean area is used for calculating the heat flow rate through a thick walled cylinder
83. Nucleate boiling is promoted
Correct : B. On rough surfaces
84. Which of the following has the lowest Prandtl number?
Correct : A. Molten sodium (a coolant used in fast breeder reactor)
85. The thermal boundary layer at NPr > 1
Correct : B. Is thinner than hydrodynamic boundary layer
86. In case of a multipass shell and tube heat exchanger, the temperature drop in the fluid
Correct : B. And the wall are proportional to individual resistances
87. Which of the following is directly concerned with the heat transfer?
Correct : D. Grashoff number
88. 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
Correct : A. Solution has an elevation of boiling point
89. The equation, Nst = f/2, is the __________ analogy.
Correct : B. Reynolds
90. Nusselt number is a function of Prandtl number and __________ number of fluid in
natural convection heat transfer.
Correct : A. Grashoff
91. Forced circulation evaporators are normally used for concentrating liquids having
Correct : C. Both (A) & (B)
92. Radiation energy is emitted by all the substances, which are above
Correct : A. 0°K
93. View factor is important in heat transfer by
Correct : D. Radiation
94. Pick out the wrong statement.
Correct : B. Two identical cubes of iron and copper will have the same heat content under the same conditions of temperature
95. 'Duhring's plot' is of use in
Correct : B. Evaporation
96. The dimensionless group in mass transfer that is equivalent to Prandtl number in heat
transfer is
Correct : C. Schmidt number
97. Pick out the wrong statement.
Correct : C. Forced convection is relatively more effective in increasing the rate of mass transfer, if Schmidt number is larger
98. Loss of heat from untagged steam pipe to the ambient air is by
Correct : D. All (A), (B) & (C)
99. In Biot number, the characteristic length used is the ratio of the __________ of the solid.
Correct : A. Volume to surface area
100. 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