1. Which type of heat exchanger is preferred for heavy heat loads?
Correct : C. Series and parallel set of shell and tube
2. For condensation of pure vapors, if the heat transfer co-efficients in filmwise and drop-wise
condensation are respectively hf and hd, then
Correct : C. hf < hd
3. The unit of heat transfer co-efficient in SI unit is
Correct : B. W/m2°K
4. Heat transfer in the laminar sub-layer in case of a liquid flowing through a pipe, is mostly
by
Correct : B. Conduction
5. If the baffle spacing in a shell and tube heat exchanger increases, then the Reynolds number of the shell side fluid
Correct : D. Decreases
6. __________ heat exchanger is the most suitable, when the temperature of shell side fluid is much higher than that of tube side.
Correct : B. U-tube
7. Fouling factor
Correct : C. Accounts for additional resistances to heat flow
8. Evaporation of 1kg of water from a solution in a single effect evaporator requires about
__________ kg of steam.
Correct : B. 1-1.3
9. As the difference between the wall temperature and bulk temperature increases, the boiling
heat transfer co-efficient
Correct : C. Goes through a minimum
10. Thermal conductivities of most of the liquids __________ with rise in temperature.
Correct : B. Decreases
11. The equivalent diameter for pressure drop is __________ that for heat transfer.
Correct : A. Smaller than
12. The purpose of providing a 'catchall' in the vapor line of an evaporator is to
Correct : D. Arrest the entrained liquid
13. Which of the following accessories is provided in the vapor line of an evaporator for
removing the entrained liquid?
Correct : C. Catchall
14. Removal of __________ heat is involved in the condensation of a vapor under saturated
conditions.
Correct : B. Sensible
15. In a heat exchanger, floating head is provided to
Correct : C. Relieve stresses caused by thermal expansion
16. The energy radiated from a surface Q at absolute temperature T is related as
Correct : B. Q ∝ T4
17. Electromagnetic radiations propagate in vacuum with a velocity of __________
metre/second.
Correct : B. 3 × 108
18. Absorptivity of a perfect black body is unity. Which of the following has maximum
absorptivity?
Correct : D. Coke breeze
19. With the increase of temperature, the Col-burn jH factor
Correct : A. Increases
20. Crystallisation of solids from a homogeneous solution is a/an __________ process.
Correct : A. Exothermic
21. Pick out the wrong statement.
Correct : A. Heat transfer by radiation cannot occur across an absolute volume
22. Steam condensate is recovered by steam traps and recycled for use as boiler feed water, because of its low
Correct : D. All (A), (B) and (C)
23. In case of a multipass shell and tube heat exchanger, providing a baffle on the shell side __________ the heat transfer rate.
Correct : A. Increases
24. __________ paint has the maximum absorption coefficient.
Correct : A. Black
25. The advantage of backward feed multiple effect evaporators over forward feed units is that
Correct : C. Most concentrated liquid is at highest temperature
26. Baffles are provided in heat exchangers to increase the
Correct : C. Heat transfer co-efficient
27. Film boiling is usually not desired in commercial equipments, because
Correct : A. The heat transfer rate is low in view of the large temperature drop
28. Pick out the wrong statement.
Correct : C. S.I. unit of fouling factor is Watt/m2 .°K
29. A dephlegmator is a
Correct : C. Partial condenser
30. Prandtl and Reynold's analogies are identical for Prandtl number value of
Correct : C. 1
31. Reynold's analogy states that (where, St = Stanton number f = friction factor)
Correct : A. St = f/2
32. The rate of heat transfer through a pipe wall is given by, q = 2π k (Ti- T0)/ln (ri /r0). For cylinder of very thin wall, q can be approximated by
Correct : D. q = 2π k (Ti- T0)/[(r0 + ri)/2]
33. Heat transfer by natural convection is enhanced in system with
Correct : B. High co-efficient of thermal expansion
34. 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
Correct : C. Increase by 216
35. At what value of Prandtl number, the hydrodynamic and thermal boundary layers of a
fluid flowing over a heated plate will be identical?
Correct : A. 1
36. 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.
Correct : D. Brinkman
37. Heat flux through several resistances in series in analogous to the current flowing through
several
Correct : C. Resistances in series
38. Heat transfer efficiency leading of energy conservation in a heat exchanger can be achieved by
Correct : A. Keeping the heat transfer surface clean
39. For a counter current heat exchanger with Ti h = 80°C, T°c = 60°C, T°h = 50°C and Ti c = 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 satisfy
Correct : B. d 2T/dZ2 = 0
40. Which is the most suitable for the concert-ration of highly concentrated solution?
Correct : A. Open pan evaporation
41. For gases, the thermal conductivity increases with temperature rise. For liquids, with
increase in concentration, its thermal conductivity generally
Correct : A. Decreases
42. A hot liquid is kept in a big room. The logarithm 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
Correct : B. Straight line
43. With increase in the distance between the heat source and the object receiving the heat, the
radiation heat transfer
Correct : A. Decreases
44. Prandtl number is the ratio of
Correct : B. Momentum diffusivity to thermal diffusivity
45. Double pipe heat exchangers are preferably useful, when
Correct : B. Requirement of heat transfer area is low
46. A hot body will radiate heat most rapidly, if its surface is
Correct : B. Black & rough
47. Rate of heat transfer by vaporisation from pools of water is affected by the
Correct : D. All (A), (B) and (C)
48. Thickness of thermal boundary layer is more compared to that of hydrodynamic boundary
layer, when the value of Prandtl number is
Correct : B. < 1
49. The purpose of providing bleed points in the evaporator is to
Correct : C. Facilitate removal of non-condensable gases
50. Choose the most important factor on which the heat conducted through a wall in a unit
time will depend on?
Correct : D. Temperature difference between the two surfaces of the wall
51. With increase in temperature, the thermal conductivity of steel
Correct : B. Decreases
52. Film boiling occurs at __________ pressure.
Correct : D. Very high
53. In a shell and tube heat exchanger, the tube side heat transfer co-efficient just at the
entrance of the tube is
Correct : A. Infinity
54. At Pr > 1, conduction in an ordinary fluid flowing through a heated pipe is limited to the
Correct : D. Viscous sub-layer
55. Which of the following is the most controlling factor for the rate of bubble detachment
from the hot solid surface?
Correct : D. Interfacial tension
56. 'Fouling factor' used in the design of a multipass shell and tube heat exchanger is a
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Correct : B. Factor of safety
57. Radiation heat transfer rates does not depend upon the
Correct : D. None of these
58. Economy of an evaporator is influenced by the
Correct : D. Both (B) & (C)
59. 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
Correct : B. 2
60. Circulation pump is located below the evaporator to
Correct : C. Create more suction head
61. Which of the following is not concerned with the heat transfer?
Correct : C. Schmidt number
62. Which of the following has the highest thermal conductivity?
Correct : D. Silver
63. __________ equation relates the thermal conductivity of a solid to its temperature.
Correct : C. Lee's
64. A hollow sphere and a solid sphere of the same material and equal radii are heated to the same temperature. In this case,
Correct : D. Both (B) & (C)
65. Unsteady state heat conduction occurs, when
Correct : B. Temperature distribution is dependent on time
66. A __________ surface has the maximum thermal emissivity out of the following.
Correct : B. Black & rough
67. For specified tube outside diameter, higher BWG means higher
Correct : B. Cross-sectional area
68. 1 BTU/hr.ft.°F is equal to __________ kcal/hr. m.°C.
Correct : A. 1.49
69. A long iron rod initially at a temperature of 20°C has one end dipped in boiling water (100°C) at time, t = 0. The curved surface of the rod is insulated so that heat conduction is one dimensional in the axial direction. The temperature at a distance 100 mm from the dipped end becomes 40°C at time, t = 200 s. The same temperature is achieved at a distance of 200 mm from the dipped end at time
Correct : D. t = 800 s
70. Multiple effect evaporation is generally recommended, when the
Correct : A. Large scale evaporation of liquor is needed
71. Value of Prandtl number for water ranges from
Correct : B. 5 to 10
72. Which of the following is correct?
Correct : B. Driving force = Rate × Resistance
73. For a fluid flowing in an annulus space, the wetted perimeter for heat transfer and
pressure drop are
Correct : B. Different
74. Steam is routed through the tube in case of a __________ evaporator.
Correct : B. Horizontal tube
75. 1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of
moisture removed in kg is
Correct : C. 400
76. The sum of reflectivity and absorptivity for an opaque body is equal to
Correct : B. 1
77. Dropwise condensation occurs on __________ surfaces.
Correct : C. Contaminated cooling
78. In a backward feed multiple effect evaporator
Correct : B. Feed flows from low pressure to high pressure
79. Conduction occurs in the buffer zone for a fluid flowing through a heated pipe, only when
Prandtl number is
Correct : A. 0.1
80. For a given ambient air temperature with increase in the thickness of insulation of a hot
cylindrical pipe, the rate of heat loss from the surface would
Correct : D. First increase and then decrease
81. In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)
Correct : D. α = 1; ε = 1
82. The type of liquor circulation system to be ' employed in evaporators (viz. natural or forced circulation) is determined mainly by the __________ of the liquid.
Correct : A. Viscosity
83. Nusselt number (for forced convection heat transfer) is a function of the __________ number.
Correct : C. Both (A) & (B)
84. In case of __________ boiling, the bubbles formed on a submerged hot surface get
absorbed in the mass of the liquid.
Correct : B. Pool
85. The separation of liquid droplets from the vapor is done by a/an __________, in the evaporators.
Correct : B. Entrainment separator
86. 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
Correct : C. 1
87. A dilute aqueous solution is to be concentrated in an evaporator system. High pressure steam is available. Multiple effect evaporator system is employed, because
Correct : B. Total amount of vapor produced per Kg of feed steam in a multiple effect system is much higher than in a single effect
88. In a boiling curve, the peak heat flux is called the __________ point.
Correct : D. Burnout
89. Film condensation is promoted on a/an __________ surface.
Correct : C. Clean & smooth
90. 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.
Correct : B. Less
91. The wavelength at which the maximum monochromatic emissive power occurs for a black body, is (where, T = absolute temperature of the black body).
Correct : B. α × 1/T
92. In a 1-1 concurrent heat exchanger, if the tube side fluid outlet temperature is equal to the
shell side fluid outlet temperature, then the LMTD is
Correct : B. 0
93. According to Reynolds analogy, Stanton number is equal to (where, f = Fanning friction
factor)
Correct : C. f/2
94. Grashoff number, which is defined as g . β (Ts - T∞) ρ2. L3/μ2, is proportional to the ratio of buoyancy force to __________ force.
Correct : A. Viscous
95. In forced circulation, the heating element is injected
Correct : A. Internally
96. 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 : C. Linear
97. Pick out the wrong statement.
Correct : D. Overall heat transfer co-efficient in a heat exchanger is controlled by the value of the film coefficient, which is higher
98. Viscous & heat sensitive liquids are concentrated in __________ evaporators.
Correct : C. Agitated film
99. When does the heat generated by fluid friction becomes appreciable compared to the heat
transferred between the fluids?
Correct : A. At high fluid velocity
100. During crystallisation, formation of crystal can occur in __________ solution only.