McqMate
These multiple-choice questions (MCQs) are designed to enhance your knowledge and understanding in the following areas: Mechanical Engineering .
| 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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