McqMate
1. |
Unit of thermal conductivity in M.K.S. units is |
A. | kcal/kg m2 °C |
B. | kcal-m/hr m2 °C |
C. | kcal/hr m2 °C |
D. | kcal-m/hr °C |
E. | kcal-m/m2 °C. |
Answer» B. kcal-m/hr m2 °C |
2. |
Unit of thermal conductivity in S.I. units is |
A. | J/m2 sec |
B. | J/m °K sec |
C. | W/m °K |
D. | a) and c) above |
E. | b) and c) above. |
Answer» E. b) and c) above. |
3. |
Thermal conductivity of solid metals with rise in temperature normally |
A. | increases |
B. | decreases |
C. | remains constant |
D. | may increase or decrease depending on temperature |
E. | unpredictable. |
Answer» B. decreases |
4. |
Thermal conductivity of non-metallic amorphous solids with decrease in temperature |
A. | increases |
B. | decreases |
C. | remains constant |
D. | may increase or decrease depending on temperature |
E. | unpredictable. |
Answer» B. decreases |
5. |
Heat transfer takes place as per – |
A. | zeroth law of thermodynamics |
B. | first law of thermodynamic |
C. | second law of the thermodynamics |
D. | Kirchoff’s law |
E. | Stefan’s law. |
Answer» 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 |
A. | conduction |
B. | convection |
C. | radiation |
D. | conduction and convection |
E. | convection and radiation. |
Answer» 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 |
A. | conduction |
B. | convection |
C. | radiation |
D. | conduction and convection |
E. | convection and radiation. |
Answer» C. radiation |
8. |
Sensible heat is the heat required to |
A. | change vapour into liquid |
B. | change liquid into vapour |
C. | increase the temperature of a liquid of vapour |
D. | convert water into steam and superheat it |
E. | convert saturated steam into dry steam. |
Answer» C. increase the temperature of a liquid of vapour |
9. |
The insulation ability of an insulator with the presence of moisture would |
A. | increase |
B. | decrease |
C. | remain unaffected |
D. | may increase/decrease depending on temperature and thickness of insulation |
E. | none of the above. |
Answer» B. decrease |
10. |
When heat is Transferred by molecular collision, it is referred to as heat transfer by |
A. | conduction |
B. | convection |
C. | radiation |
D. | scattering |
E. | convection and radiation. |
Answer» B. convection |
11. |
Heat transfer in liquid and gases takes place by |
A. | conduction |
B. | convection |
C. | radiation |
D. | conduction and convection |
E. | convection and radiation. |
Answer» B. convection |
12. |
Which of the following is the case of heat transfer by radiation |
A. | blast furnace |
B. | heating of building |
C. | cooling of parts in furnace |
D. | heat received by a person from fireplace |
E. | all of the above. |
Answer» D. heat received by a person from fireplace |
13. |
Heat is closely related with |
A. | liquids |
B. | energy |
C. | temperature |
D. | entropy |
E. | enthalpy. |
Answer» C. temperature |
14. |
Pick up the wrong case. Heat flowing from one side to other depends directly on |
A. | face area |
B. | time |
C. | thickness |
D. | temperature difference |
E. | thermal conductivity. |
Answer» C. thickness |
15. |
Metals are good conductors of heat because |
A. | their atoms collide frequently |
B. | their atoms-are relatively far apart |
C. | they contain free electrons |
D. | they have high density |
E. | all of the above. |
Answer» A. their atoms collide frequently |
16. |
Which of the following is a case of steady state heat transfer |
A. | I.C. engine |
B. | air preheaters |
C. | heating of building in winter |
D. | all of the above |
E. | none of the above. |
Answer» E. none of the above. |
17. |
Total heat is the heat required to |
A. | change vapour into liquid |
B. | change liquid into vapour |
C. | increase the temperature of a liquid or vapour |
D. | convert water into steam and superheat it |
E. | convert saturated steam into dry steam. |
Answer» D. convert water into steam and superheat it |
18. |
Cork is a good insulator because it has |
A. | free electrons |
B. | atoms colliding frequency |
C. | low density |
D. | porous body |
E. | all of the above. |
Answer» D. porous body |
19. |
Thermal conductivity of water in general with rise in temperature |
A. | increases |
B. | decreases |
C. | remains constant |
D. | may increase or decrease depending on temperature |
E. | none of the above. |
Answer» D. may increase or decrease depending on temperature |
20. |
Thermal conductivity of water at 20°C is of the order of |
A. | 0.1 |
B. | 0.23 |
C. | 0.42 |
D. | 0.51 |
E. | 0.64. |
Answer» D. 0.51 |
21. |
Temperature of steam at around 540°C can be measured by |
A. | thermometer |
B. | radiatiouv pyrometer |
C. | thermistor |
D. | thermocouple |
E. | thermopile. |
Answer» D. thermocouple |
22. |
Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of |
A. | 0.002 |
B. | 0.02 |
C. | 0.01 |
D. | 0.1 |
E. | 0.5. |
Answer» B. 0.02 |
23. |
The time constant of a thermocouple is |
A. | the time taken to attain the final temperature to be measured |
B. | the time taken to attain 50% of the value of initial temperature difference |
C. | the time taken to attain 63.2% of the value of initial temperature difference |
D. | determined by the time taken to reach 100°C from 0°C |
E. | none of the above. |
Answer» C. the time taken to attain 63.2% of the value of initial temperature difference |
24. |
Thermal conductivity of air with rise in temperature |
A. | increases |
B. | decreases |
C. | remains constant |
D. | may increase or decrease depending on temperature |
E. | none of the above. |
Answer» A. increases |
25. |
Heat flows from one body to other when they have |
A. | different heat contents |
B. | different specific heat |
C. | different atomic structure |
D. | different temperatures |
E. | none of the above. |
Answer» D. different temperatures |
26. |
The concept of overall coefficient of heat transfer is used in heat transfer problems of |
A. | conduction |
B. | convection |
C. | radiation |
D. | all the three combined |
E. | conduction and comte_ction. |
Answer» E. conduction and comte_ction. |
27. |
In heat transfer, conductance equals conductivity (kcal/hr/sqm/°C/cm) divided by |
A. | hr (time) |
B. | sqm (area) |
C. | °C (temperature) |
D. | cm (thickness) |
E. | kcal (heat). |
Answer» D. cm (thickness) |
28. |
The amount of heat flow through a body by conduction is |
A. | directly proportional to the surface area of the body |
B. | directly proportional to the temperature difference on the two faces of the body |
C. | dependent upon the material of the body |
D. | inversely proportional to the thickness of the body |
E. | all of the above. |
Answer» E. all of the above. |
29. |
Which of the following has least value of conductivity |
A. | glass |
B. | water |
C. | plastic |
D. | rubber |
E. | air. |
Answer» E. air. |
30. |
Which of the following is expected to have highest thermal conductivity |
A. | steam |
B. | solid ice |
C. | melting ice |
D. | water |
E. | boiling water. |
Answer» B. solid ice |
31. |
Thermal conductivity of glass-wool varies from sample to sample because of variation in |
A. | composition |
B. | density |
C. | porosity |
D. | structure |
E. | all of the above. |
Answer» E. all of the above. |
32. |
Thermal conductivity of a material may be defined as the |
A. | quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C |
B. | quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C |
C. | heat conducted in unit time across unit area through unit thickness when a temperature difference of unity is maintained between opposite faces |
D. | all of the above |
E. | none of the above. |
Answer» D. all of the above |
33. |
Which of the following has maximum value of thermal conductivity |
A. | aluminium |
B. | steel |
C. | brass |
D. | copper |
E. | lead. |
Answer» A. aluminium |
34. |
Moisture would find its way into insulation by vapour pressure unless it is prevented by |
A. | high thickness of insulation |
B. | high vapour pressure |
C. | less thermal conductivity insulator |
D. | a vapour seal |
E. | all of the above. |
Answer» D. a vapour seal |
35. |
Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in |
A. | electric heater |
B. | steam condenser |
C. | melting of ice |
D. | refrigerator condenser coils |
E. | boiler. |
Answer» E. boiler. |
36. |
According to Prevost theory of heat exchange |
A. | it is impossible to transfer heat from low temperature source to t high temperature source |
B. | heat transfer by radiation requires no medium |
C. | all bodies above absolute zero emit radiation |
D. | heat transfer in most of the cases takes place by combination of conduction, convection and radiation |
E. | rate of heat transfer depends on thermal conductivity and temperature difference. |
Answer» 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 |
A. | I |
B. | 0.5 |
C. | 2 |
D. | 0.25 |
E. | 4.0 |
Answer» C. 2 |
38. |
Heat transfer by radiation mainly depends upon |
A. | its temperature |
B. | nature of the body |
C. | kind and extent of its surface |
D. | all of the above |
E. | none of the above. |
Answer» D. all of the above |
39. |
Thermal diffusivity is |
A. | a dimensionless parameter |
B. | function of temperature |
C. | used as mathematical model |
D. | a physical property of the material |
E. | useful in case of heat transfer by radiation. |
Answer» D. a physical property of the material |
40. |
Thermal diffusivity of a substance is . |
A. | proportional of thermal conductivity |
B. | inversely proportional to k |
C. | proportional to (k) |
D. | inversely proportional to k2 |
E. | none of the above. |
Answer» A. proportional of thermal conductivity |
41. |
Unit of thermal diffusivity is |
A. | m2/hr |
B. | m2/hr°C |
C. | kcal/m2 hr |
D. | kcal/m.hr°C |
E. | kcal/m2 hr°C. |
Answer» A. m2/hr |
42. |
Thermal conductivity of wood depends on |
A. | moisture |
B. | density |
C. | temperature |
D. | all of the above |
E. | none of the above. |
Answer» 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 |
A. | convection |
B. | radiation |
C. | conduction |
D. | both convection and conduction |
E. | none of the above. |
Answer» C. conduction |
44. |
Film coefficient is defined as Inside diameter of tube |
A. | Equivalent thickness of film |
B. | Thermal conductivity Equivalent thickness of film Specific heat x Viscocity |
C. | Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity |
D. | Film coefficient x Inside diameter Thermalconductivity |
E. | none of the above. |
Answer» 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 |
A. | thermal resistance |
B. | thermal coefficient |
C. | temperature gradient |
D. | thermal conductivity |
E. | heat-transfer. |
Answer» 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 |
A. | emissivity |
B. | transmissivity |
C. | reflectivity |
D. | intensity of radiation |
E. | absorptivity. |
Answer» D. intensity of radiation |
47. |
Emissivity of a white polished body in comparison to a black body is |
A. | higher |
B. | lower |
C. | same |
D. | depends upon the shape of body |
E. | none of the above. |
Answer» B. lower |
48. |
A grey body is one whose absorptivity |
A. | varies with temperature |
B. | varies with wavelength of the incident ray |
C. | is equal to its emissivity |
D. | does not vary with temperature and. wavelength of the incident ray |
E. | none of the above. |
Answer» 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 |
A. | 1 :1 |
B. | 2: 1 |
C. | 1 : 2 |
D. | 4 : 1 |
E. | 1 : 4. |
Answer» C. 1 : 2 |
50. |
A non-dimensional number generally associated with natural convection heat transfer is |
A. | Grashoff number |
B. | Nusselt number |
C. | Weber number |
D. | Prandtl number |
E. | Reynold number. |
Answer» A. Grashoff number |
51. |
LMTD in case of counter flow heat exchanger as compared-to parallel flow heat exchanger is |
A. | higher |
B. | lower |
C. | same |
D. | depends on the area of heat exchanger |
E. | depends on temperature conditions. |
Answer» A. higher |
52. |
In heat exchangers, degree of approach is defined as the difference between temperatures of |
A. | cold water inlet and outlet |
B. | hot medium inlet and outlet |
C. | hot medium outlet and cold water inlet |
D. | hot medium outlet and cold water outlet |
E. | none of the above. |
Answer» D. hot medium outlet and cold water outlet |
53. |
In counter flow heat exchangers |
A. | both the fluids at inlet (of heat ex¬changer where hot fluid enters) are in their coldest state |
B. | both the fluids at inlet are in their hot¬test state |
C. | both the fluids .at exit are in their hottest state |
D. | one fluid is in hottest state and other in coldest state at inlet |
E. | any combination is possible depending on design of heat exchanger. |
Answer» 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 |
A. | better insulation should be put over pipe and better one over it |
B. | inferior insulation should be put over pipe and better one over it |
C. | both may be put in any order |
D. | whether to put inferior OIL over pipe or the better one would depend on steam temperature |
E. | unpredictable. |
Answer» A. better insulation should be put over pipe and better one over it |
55. |
Fourier’s law of heat conduction is valid for |
A. | one dimensional cases only |
B. | two dimensional cases only |
C. | three dimensional cases only |
D. | regular surfaces having non-uniform temperature gradients |
E. | irregular surfaces. |
Answer» A. one dimensional cases only |
56. |
According of Kirchhoff’s law, |
A. | radiant heat is proportional to fourth power of absolute temperature |
B. | emissive power depends on temperature |
C. | emissive power and absorptivity are constant for all bodies |
D. | ratio of emissive power to absorptive power is maximum for perfectly black body |
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. |
Answer» 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 |
A. | reflected |
B. | refracted |
C. | transmitted |
D. | absorbed |
E. | partly reflected and partly absorbed. |
Answer» 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 |
A. | grey body |
B. | brilliant white polished body |
C. | red hot body |
D. | black body |
E. | none of the above. |
Answer» D. black body |
59. |
The concept of overall coefficient of heat transfer is used in case of heat transfer by |
A. | conduction |
B. | convection |
C. | radiation |
D. | conduction and convection |
E. | convection and radiation. |
Answer» D. conduction and convection |
60. |
Joule sec is the unit of |
A. | universal gas constant |
B. | kinematic viscosity |
C. | thermal conductivity |
D. | Planck’s constant |
E. | none of the above. |
Answer» D. Planck’s constant |
61. |
The value of Prandtl number for air is about |
A. | 0.1 |
B. | 0.3 |
C. | 0.7 |
D. | 1.7 |
E. | 10.5. |
Answer» C. 0.7 |
62. |
The value of the wavelength for maximum emissive power is given by — |
A. | Wien’s law |
B. | Planck’s law |
C. | Stefan’s law |
D. | Fourier’s law |
E. | Kirchhoff’s law. |
Answer» A. Wien’s law |
63. |
Log mean temperature difference in case of counter flow compared to parallel flow will be |
A. | same |
B. | more |
C. | less |
D. | depends on other factors |
E. | none of the above. |
Answer» B. more |
64. |
The energy distribution of an ideal reflector at higher temperatures is largely in the range of |
A. | shorter wavelength |
B. | longer wavelength |
C. | remains same at all wavelengths |
D. | wavelength has nothing to do with it |
E. | none of the above. |
Answer» A. shorter wavelength |
65. |
Total emissivity of polished silver compared to black body is |
A. | same |
B. | higher |
C. | more or less same |
D. | very much lower |
E. | very much higher. |
Answer» D. very much lower |
66. |
According to Stefan-Boltzmann law, ideal radiators emit radiant energy at a rate proportional to |
A. | absolute temperature |
B. | square of temperature |
C. | fourth power of absolute temperature |
D. | fourth power of temperature |
E. | cube of absolute temperature. |
Answer» C. fourth power of absolute temperature |
67. |
Which of the following property of air does not increase with rise in temperature |
A. | thermal conductivity |
B. | thermal diffusivity |
C. | density |
D. | dynamic viscosity |
E. | kuiematic viscosity. |
Answer» C. density |
68. |
The unit of Stefan Boltzmann constant is |
A. | watt/cm2 °K |
B. | watt/cm4 °K |
C. | watt2/cm °K4 |
D. | watt/cm2 °K4 |
E. | watt/cm2 °K2. |
Answer» D. watt/cm2 °K4 |
69. |
In free con-vection heat transfer, Nusselt number is function of |
A. | Grashoff no. and Reynold no. |
B. | Grashoff no. and Prandtl no. |
C. | Prandtl no. and Reynold no. |
D. | Grashoff no., Prandtl no. and Reynold no. |
E. | none of the above. |
Answer» B. Grashoff no. and Prandtl no. |
70. |
Stefan Boltzmann law is applicable for heat transfer by |
A. | conduction |
B. | convection |
C. | radiation |
D. | conduction and radiation combined |
E. | convection and radiation combined. |
Answer» C. radiation |
71. |
The thermal diffusivities for gases are generally |
A. | more than those for liquids |
B. | less than those for liquids |
C. | more than those for solids |
D. | dependent on the viscosity |
E. | same as for the liquids. |
Answer» A. more than those for liquids |
72. |
The thermal diffusivities for solids are generally |
A. | less than those for gases |
B. | jess than those for liquids |
C. | more than those for liquids and gases |
D. | more or less same as for liquids and gases |
E. | zerci. |
Answer» C. more than those for liquids and gases |
73. |
Thermal diffusivity of a substance is |
A. | directly proportional to thermal con¬ductivity |
B. | inversely proportional to density of substance |
C. | inversely proportional to specific heat |
D. | all of the above |
E. | none of the above. |
Answer» 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 |
A. | Krichoff’s law |
B. | Stefan’s law |
C. | Wien’ law |
D. | Planck’s law |
E. | Black body law. |
Answer» 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 |
A. | absolute temperature |
B. | T2 |
C. | T5 |
D. | t |
E. | l/T. |
Answer» D. t |
76. |
According to Wien’s law, the wavelength corresponding to maximum energy is proportion to |
A. | absolute temperature (T) |
B. | I2 |
C. | f |
D. | t |
E. | 1/r. |
Answer» A. absolute temperature (T) |
77. |
Depending on the radiating properties, a body will be white when (where a = absorptivity, p = reflectivity, x = transmissivity) |
A. | p = 0, x = 0 and a = 1 |
B. | p=l,T = 0anda = 0 |
C. | p = 0, x = 1 and a = 0 |
D. | x = 0, a + p = 1 |
E. | a = 0, x + p = 1. |
Answer» 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.) |
A. | p = 0, x = 0 and a = 1 |
B. | p= l,T = 0anda = 0 |
C. | p = 0, x = 1 and a = 0 |
D. | x = 0, a + p = 0 |
E. | a = 0,x + p= 1. |
Answer» 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.) |
A. | p = 0, x = 0 and a = 1 |
B. | p=l,x = 0anda = 0 |
C. | p = 0, x = 1 and a = 0 |
D. | x – 0, a + p = 1 |
E. | a=0,x + p= 1. |
Answer» 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 |
A. | temperature |
B. | thickness |
C. | area |
D. | time |
E. | area and time. |
Answer» D. time |
81. |
The ratio of the energy absorbed by the body to total energy falling on it is called |
A. | absorptive power |
B. | emissive power |
C. | absorptivity |
D. | emissivity |
E. | none of the above. |
Answer» 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 |
A. | 0.45 |
B. | 0.55 |
C. | 0.40 |
D. | 0.75 |
E. | 0.60. |
Answer» A. 0.45 |
83. |
The amount of radiation mainly depends on |
A. | nature of body |
B. | temperature of body |
C. | type of surface of body |
D. | all of the above |
E. | none of the above. |
Answer» D. all of the above |
84. |
The emissive power of a body depends upon its |
A. | temperature |
B. | wave length |
C. | physical nature |
D. | all of the above |
E. | none of the above. |
Answer» 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 |
A. | convection |
B. | free convection |
C. | forced convection |
D. | radiation |
E. | radiation and convection. |
Answer» D. radiation |
86. |
Absorptivity of a body will be equal to its emissivity |
A. | at all temperatures |
B. | at one particular temperature |
C. | when system is under thermal equi-librium |
D. | at critical temperature |
E. | for a polished body. |
Answer» C. when system is under thermal equi-librium |
87. |
In regenerator type heat exchanger, heat transfer takes place by |
A. | direct mixing of hot and cold fluids |
B. | a complete separation between hot and cold fluids |
C. | flow of hot and cold fluids alternately over a surface |
D. | generation of heat again and again |
E. | indirect transfer. |
Answer» C. flow of hot and cold fluids alternately over a surface |
88. |
A perfect black body is one which |
A. | is black in colour |
B. | reflects all heat |
C. | transmits all heat radiations |
D. | abslprbs heat radiations of all wave lengths falling on it |
E. | fully opaque. |
Answer» D. abslprbs heat radiations of all wave lengths falling on it |
89. |
Planck’s law holds good for |
A. | black bodies |
B. | polished bodies |
C. | all coloured bodies |
D. | all of the above |
E. | none of the above. |
Answer» 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 |
A. | 3 |
B. | 6 |
C. | 9 |
D. | 27 |
E. | 81. |
Answer» E. 81. |
91. |
Depending on the radiating properties, body will be transparent when |
A. | p = 0, x = 0 and a = 1 |
B. | p=l,x = 0,anda = 0 |
C. | p = 0, T= l,anda = 0 |
D. | X = 0, a + p = 1 |
E. | a = 0,x + p= 1. |
Answer» C. p = 0, T= l,anda = 0 |
92. |
A grey body is one whose absorptivity |
A. | varies with temperature |
B. | varies with the wave length of incident ray |
C. | varies with both |
D. | does not vary with temperature and wave length of the incident ray |
E. | there is no such criterion. |
Answer» 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. |
A. | 1 |
B. | 10 |
C. | 20 |
D. | 30 |
Answer» 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 |
A. | Decreases the pressure drop |
B. | Decreases the outlet temperature of cooling medium |
C. | Increases the overall heat transfer coefficient |
D. | None of these |
Answer» 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? |
A. | Yellow paint |
B. | White paint |
C. | Black paint |
D. | Grey paint |
Answer» 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? |
A. | 35.5 |
B. | 43.75 |
C. | 81.25 |
D. | 48.25 |
Answer» 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. |
A. | 40 |
B. | 95 |
C. | 70 |
D. | 50 |
Answer» C. 70 |
98. |
A graph between __________ is called Wilson plot. |
A. | (1/U) Vs. (1/v 0.8) |
B. | (1/v 0.8) Vs. U |
C. | v 0.8 Vs . U |
D. | (1/U) Vs. (1/V) |
Answer» 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 |
A. | Black painted bodies only |
B. | All bodies |
C. | Polished bodies only |
D. | A black body |
Answer» 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 |
A. | 1.26 h1 |
B. | 0.794 h1 |
C. | 0.574 h1 |
D. | 1.741 h1 |
Answer» B. 0.794 h1 |
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