1. Unit of thermal conductivity in M.K.S. units is
Correct : B. kcal-m/hr m2 °C
2. Unit of thermal conductivity in S.I. units is
Correct : E. b) and c) above.
3. Thermal conductivity of solid metals with rise in temperature normally
Correct : B. decreases
4. Thermal conductivity of non-metallic amorphous solids with decrease in
temperature
Correct : B. decreases
5. Heat transfer takes place as per –
Correct : C. second law of the thermodynamics
6. When heat is transferred from one particle of hot body to another by actual
motion of the heated particles, it is referred to as heat transfer by
Correct : A. conduction
7. When heat is transferred form hot body to cold body, in a straight line, without
affecting the intervening medium, it is referred as heat transfer by
Correct : C. radiation
8. Sensible heat is the heat required to
Correct : C. increase the temperature of a liquid of vapour
9. The insulation ability of an insulator with the presence of moisture would
Correct : B. decrease
10. When heat is Transferred by molecular collision, it is referred to as heat
transfer by
Correct : B. convection
11. Heat transfer in liquid and gases takes place by
Correct : B. convection
12. Which of the following is the case of heat transfer by radiation
Correct : D. heat received by a person from fireplace
13. Heat is closely related with
Correct : C. temperature
14. Pick up the wrong case. Heat flowing from one side to other depends directly
on
Correct : C. thickness
15. Metals are good conductors of heat because
Correct : A. their atoms collide frequently
16. Which of the following is a case of steady state heat transfer
Correct : E. none of the above.
17. Total heat is the heat required to
Correct : D. convert water into steam and superheat it
18. Cork is a good insulator because it has
Correct : D. porous body
19. Thermal conductivity of water in general with rise in temperature
Correct : D. may increase or decrease depending on temperature
20. Thermal conductivity of water at 20°C is of the order of
Correct : D. 0.51
21. Temperature of steam at around 540°C can be measured by
Correct : D. thermocouple
22. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order
of
Correct : B. 0.02
23. The time constant of a thermocouple is
Correct : C. the time taken to attain 63.2% of the value of initial temperature difference
24. Thermal conductivity of air with rise in temperature
Correct : A. increases
25. Heat flows from one body to other when they have
Correct : D. different temperatures
26. The concept of overall coefficient of heat transfer is used in heat transfer
problems of
Correct : E. conduction and comte_ction.
27. In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided
by
Correct : D. cm (thickness)
28. The amount of heat flow through a body by conduction is
Correct : E. all of the above.
29. Which of the following has least value of conductivity
Correct : E. air.
30. Which of the following is expected to have highest thermal conductivity
Correct : B. solid ice
31. Thermal conductivity of glass-wool varies from sample to sample because of
variation in
Correct : E. all of the above.
32. Thermal conductivity of a material may be defined as the
Correct : D. all of the above
33. Which of the following has maximum value of thermal conductivity
Correct : A. aluminium
34. Moisture would find its way into insulation by vapour pressure unless it is
prevented by
Correct : D. a vapour seal
35. Heat is transferred by all three modes of transfer, viz, conduction, convection
and radiation in
Correct : E. boiler.
36. According to Prevost theory of heat exchange
Correct : C. all bodies above absolute zero emit radiation
37. The ratio of heat flow Q1/Q2 from two walls of same thickness having their thermal conductivities as ATj – 2K2 will be
Correct : C. 2
38. Heat transfer by radiation mainly depends upon
Correct : D. all of the above
39. Thermal diffusivity is
Correct : D. a physical property of the material
40. Thermal diffusivity of a substance is .
Correct : A. proportional of thermal conductivity
41. Unit of thermal diffusivity is
Correct : A. m2/hr
42. Thermal conductivity of wood depends on
Correct : D. all of the above
43. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
Correct : C. conduction
44. Film coefficient is defined as Inside diameter of tube
Correct : B. Thermal conductivity Equivalent thickness of film Specific heat x Viscocity
45. Heat conducted througfi unit area and unit thick face per unit time when
temperature difference between opposite faces is unity,is called
Correct : D. thermal conductivity
46. The rate of energy emission from unit surface area through unit solid angle,
along a normal to the surface, is known as
Correct : D. intensity of radiation
47. Emissivity of a white polished body in comparison to a black body is
Correct : B. lower
48. A grey body is one whose absorptivity
Correct : C. is equal to its emissivity
49. Two balls of same material and finish have their diameters in the ratio of 2 : 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
Correct : C. 1 : 2
50. A non-dimensional number generally associated with natural convection heat
transfer is
Correct : A. Grashoff number
51. LMTD in case of counter flow heat exchanger as compared-to parallel flow heat
exchanger is
Correct : A. higher
52. In heat exchangers, degree of approach is defined as the difference between
temperatures of
Correct : D. hot medium outlet and cold water outlet
53. In counter flow heat exchangers
Correct : B. both the fluids at inlet are in their hot¬test state
54. A steam pipe is to be insulated by two insulating materials put over each other.
For best results
Correct : A. better insulation should be put over pipe and better one over it
55. Fourier’s law of heat conduction is valid for
Correct : A. one dimensional cases only
56. According of Kirchhoff’s law,
Correct : E. ratio of emissive power to absorptive power for all bodies is same and is equal to the emissive power of a perfectly black body.
57. All radiations in a black body are
Correct : D. absorbed
58. According to Kirchoff’s law, the ratio of emissive power to absorptivity for all bodies is equal to the emissive power of a
Correct : D. black body
59. The concept of overall coefficient of heat transfer is used in case of heat transfer by
Correct : D. conduction and convection
60. Joule sec is the unit of
Correct : D. Planck’s constant
61. The value of Prandtl number for air is about
Correct : C. 0.7
62. The value of the wavelength for maximum emissive power is given by —
Correct : A. Wien’s law
63. Log mean temperature difference in case of counter flow compared to parallel
flow will be
Correct : B. more
64. The energy distribution of an ideal reflector at higher temperatures is largely in
the range of
Correct : A. shorter wavelength
65. Total emissivity of polished silver compared to black body is
Correct : D. very much lower
66. According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate
proportional to
Correct : C. fourth power of absolute temperature
67. Which of the following property of air does not increase with rise in temperature
Correct : C. density
68. The unit of Stefan Boltzmann constant is
Correct : D. watt/cm2 °K4
69. In free con-vection heat transfer, Nusselt number is function of
Correct : B. Grashoff no. and Prandtl no.
70. Stefan Boltzmann law is applicable for heat transfer by
Correct : C. radiation
71. The thermal diffusivities for gases are generally
Correct : A. more than those for liquids
72. The thermal diffusivities for solids are generally
Correct : C. more than those for liquids and gases
73. Thermal diffusivity of a substance is
Correct : D. all of the above
74. The ratio of the emissive power and absorptive power of all bodies is the same and is equal to the emissive power of a perfectly black body. This statement is known as
Correct : A. Krichoff’s law
75. According to Stefan’s law, the total radiation from a black body per second per
unit area is proportional to
Correct : D. t
76. According to Wien’s law, the wavelength corresponding to maximum energy is
proportion to
Correct : A. absolute temperature (T)
77. Depending on the radiating properties, a body will be white when (where a = absorptivity, p = reflectivity, x = transmissivity)
Correct : B. p=l,T = 0anda = 0
78. Depending on the radiating properties, a body will be black when (where a = absorptivity, p == reflectivity, X = transmissivity.)
Correct : A. p = 0, x = 0 and a = 1
79. Depending on the radiating properties, a body will be opaque when (where a = absorptivity, p = reflectivity, X = transmissivity.)
Correct : D. x – 0, a + p = 1
80. The total emissivity power is .defined as the total amount of radiation emitted by
a black body per unit
Correct : D. time
81. The ratio of the energy absorbed by the body to total energy falling on it is called
Correct : A. absorptive power
82. 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is
Correct : A. 0.45
83. The amount of radiation mainly depends on
Correct : D. all of the above
84. The emissive power of a body depends upon its
Correct : D. all of the above
85. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat
transfer will take place mainly by
Correct : D. radiation
86. Absorptivity of a body will be equal to its emissivity
Correct : C. when system is under thermal equi-librium
87. In regenerator type heat exchanger, heat transfer takes place by
Correct : C. flow of hot and cold fluids alternately over a surface
88. A perfect black body is one which
Correct : D. abslprbs heat radiations of all wave lengths falling on it
89. Planck’s law holds good for
Correct : A. black bodies
90. If the temperature of a solid surface changes form 27°C to 627°C, then its
emissive power changes in the ratio of
Correct : E. 81.
91. Depending on the radiating properties, body will be transparent when
Correct : C. p = 0, T= l,anda = 0
92. A grey body is one whose absorptivity
Correct : D. does not vary with temperature and wave length of the incident ray
93. Maximum water velocity in tubes of a 1-2 shell and tube heat exchanger may be around __________ metres/second.
Correct : A. 1
94. 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
Correct : C. Increases the overall heat transfer coefficient
95. A tank painted with which of the following coloured paints, would heat up maximum by radiation from sun?
Correct : C. Black paint
96. 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 coefficient is „3k/l’. If the wall temperature on the outside is held at 25°C, what is the inside wall temperature in degree centigrade?
Correct : C. 81.25
97. Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of __________ °C.
Correct : C. 70
98. A graph between __________ is called Wilson plot.
Correct : A. (1/U) Vs. (1/v 0.8)
99. 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
Correct : B. All bodies
100. 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