MCQOPTIONS
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MCQOPTIONS
This section includes 265 Mcqs, each offering curated multiple-choice questions to sharpen your Mechanical Engineering knowledge and support exam preparation. Choose a topic below to get started.
| 51. |
When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be |
| A. | cooled and humidified |
| B. | cooled and dehumidified |
| C. | heated and humidified |
| D. | heated and dehumidified |
| Answer» B. cooled and dehumidified | |
| 52. |
The refrigerant used in small-tonnage commercial machines (hermetically sealed units) is |
| A. | ammonia |
| B. | carbon dioxide |
| C. | sulphur dioxide |
| D. | R-12 |
| Answer» D. R-12 | |
| 53. |
During sensible heating of air __________ decreases. |
| A. | wet bulb temperature |
| B. | relative humidity |
| C. | dry bulb temperature |
| D. | specific humidity |
| Answer» C. dry bulb temperature | |
| 54. |
The overall coefficient of heat transfer is used in problems of |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | conduction and convection |
| Answer» E. | |
| 55. |
The boiling point of R-12 is about - 30°C. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 56. |
The temperature of air recorded by a thermometer, when it is not effected by the moisture present in the air, is called |
| A. | wet bulb temperature |
| B. | dry bulb temperature |
| C. | dew point temperature |
| D. | none of these |
| Answer» C. dew point temperature | |
| 57. |
A human body feels comfortable when the heat produced by the metabolism of human body is equal to the |
| A. | heat dissipated to the surroundings |
| B. | heat stored in the human body |
| C. | sum of (a) and (b) |
| D. | difference of (a) and (b) |
| Answer» D. difference of (a) and (b) | |
| 58. |
During sensible cooling, |
| A. | relative humidity remains constant |
| B. | wet bulb temperature increases |
| C. | specific humidity increases |
| D. | partial pressure of vapour remains constant |
| Answer» E. | |
| 59. |
The wave length of the radiation emitted depends only on the temperature and is independent of the material of the body. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 60. |
The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called |
| A. | conduction |
| B. | convection |
| C. | radiation |
| Answer» C. radiation | |
| 61. |
Most air cooled condensers are designed to operate with a temperature difference of |
| A. | 5°C |
| B. | 8°C |
| C. | 14°C |
| D. | 22°C |
| Answer» D. 22°C | |
| 62. |
The heat transfer from a hot body to a cold body is directly proportional to the surface area and difference of temperatures between the two bodies. This statement is called |
| A. | First law of thermodynamics |
| B. | Newton's law of cooling |
| C. | Newton's law of heating |
| D. | Stefan's law |
| Answer» C. Newton's law of heating | |
| 63. |
The pressure at the inlet of a refrigerant compressor is called |
| A. | suction pressure |
| B. | discharge pressure |
| C. | critical pressure |
| D. | back pressure |
| Answer» B. discharge pressure | |
| 64. |
The process, generally used in summer air conditioning to cool and dehumidify the air, is called |
| A. | humidification |
| B. | dehumidification |
| C. | heating and humidification |
| D. | cooling and dehumidification |
| Answer» E. | |
| 65. |
Stefan-Boltzmann law is applicable for heat transfer by convection. |
| A. | Agree |
| B. | Disagree |
| Answer» C. | |
| 66. |
The most commonly used method for the design of duct size is the |
| A. | velocity reduction method |
| B. | equal friction method |
| C. | static regain method |
| D. | dual or double method |
| Answer» D. dual or double method | |
| 67. |
In counter-current flow heat exchangers |
| A. | both the fluids at inlet are in their hottest state |
| B. | both the fluids at inlet are in their coldest state |
| C. | both the fluids at exit are in their hottest state |
| D. | one fluid is coldest and the other is hottest at inlet |
| Answer» B. both the fluids at inlet are in their coldest state | |
| 68. |
The rate of heat flow through a body is . The term / is known as |
| A. | thermal coefficient |
| B. | thermal resistance |
| C. | thermal conductivity |
| D. | none of these |
| Answer» C. thermal conductivity | |
| 69. |
A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be |
| A. | 1/4 |
| B. | 1/3 |
| C. | 3 |
| D. | 4 |
| Answer» E. | |
| 70. |
In a shell and tube heat exchanger, baffles are provided on the shell side to |
| A. | improve heat transfer |
| B. | provide support for tubes |
| C. | prevent stagnation of shell side fluid |
| D. | all of these |
| Answer» E. | |
| 71. |
The average value of thermal conductivity for water at 20° C saturate is about 0.51. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 72. |
In aqua-ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in |
| A. | condenser |
| B. | evaporator |
| C. | absorber |
| D. | none of these |
| Answer» B. evaporator | |
| 73. |
In case of sensible heating of air, the coil efficiency is given by (where B.P.F. = By-pass factor) |
| A. | B.P.F. - 1 |
| B. | 1 - B.P.F. |
| C. | 1 + B.RF. |
| Answer» C. 1 + B.RF. | |
| 74. |
The coefficient of performance (C.O.P.) is the reciprocal of the efficiency of a heat engine. |
| A. | True |
| B. | False |
| Answer» B. False | |
| 75. |
The wet bulb temperature at 100% relative humidity is __________ dry bulb temperature. |
| A. | same as |
| B. | lower than |
| C. | higher than |
| Answer» B. lower than | |
| 76. |
The ratio of the energy absorbed by the body to the total energy falling on it, is called |
| A. | absorptive power |
| B. | emissive power |
| C. | emissivity |
| D. | none of these |
| Answer» B. emissive power | |
| 77. |
The coefficient of performance of a domestic refrigerator is __________ as compared to a domestic air-conditioner. |
| A. | same |
| B. | less |
| C. | more |
| Answer» C. more | |
| 78. |
The human body feels comfortable when the heat stored in the body is |
| A. | positive |
| B. | negative |
| C. | zero |
| D. | none of these |
| Answer» D. none of these | |
| 79. |
A Bell Coleman refrigerator working on dense air system as compared to open air system, for the same range of temperature, results in __________ power per tonne of refrigeration. |
| A. | same |
| B. | lower |
| C. | higher |
| Answer» C. higher | |
| 80. |
A furnace is made of a red brick wall of thickness 0.5 m and conductivity 0.7 W/mK. For the same heat loss and temperature drop, this can be replaced by a layer of diatomite earth of conductivity 0.14 W/mK and thickness |
| A. | 0.5 m |
| B. | 0.1 m |
| C. | 0.2 m |
| D. | 0.5 m |
| Answer» C. 0.2 m | |
| 81. |
In a refrigeration system, the expansion device is connected between the |
| A. | compressor and condenser |
| B. | condenser and receiver |
| C. | receiver and evaporator |
| D. | evaporator and compressor |
| Answer» D. evaporator and compressor | |
| 82. |
The heat rejection factor (HRF) is given by |
| A. | 1 + C.O.P |
| B. | 1 - C.O.P. |
| Answer» D. | |
| 83. |
Wein's law states that the wave length corresponding to __________ is proportional to the absolute temperature. |
| A. | minimum energy |
| B. | maximum energy |
| Answer» C. | |
| 84. |
An electric cable of aluminium conductor ( = 240 W/mK) is to be insulated with rubber ( = 0.15 W/mK). The cable is to be located in air ( = 6 W/m). The critical thickness of insulation will be |
| A. | 25 mm |
| B. | 40 mm |
| C. | 160 mm |
| D. | 800 mm |
| Answer» B. 40 mm | |
| 85. |
A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of , and respectively. The average heat transfer coefficient for the cube is |
| A. | + |
| B. | + |
| C. | ( |
| D. | ) |
| E. | none of these |
| Answer» E. none of these | |
| 86. |
The dehumidification process, on the psychrometric chart, is shown by |
| A. | horizontal Sine |
| B. | vertical line |
| C. | inclined line |
| D. | curved line |
| Answer» C. inclined line | |
| 87. |
The vertical and uniformly spaced lines on a psychrometric chart indicates |
| A. | dry bulb temperature |
| B. | wet bulb temperature |
| C. | dew point temperature |
| D. | specific humidity |
| Answer» B. wet bulb temperature | |
| 88. |
Thermal conductivity of solid metals __________ with rise in temperature. |
| A. | remains same |
| B. | decreases |
| C. | increases |
| Answer» C. increases | |
| 89. |
The horizontal and non-uniformly spaced lines on a psychrometric chart indicates |
| A. | dry bulb temperature |
| B. | wet bulb temperature |
| C. | dew point temperature |
| D. | specific humidity |
| Answer» D. specific humidity | |
| 90. |
A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be |
| A. | 1.33 |
| B. | 2.33 |
| C. | 3.33 |
| D. | 4.33 |
| Answer» C. 3.33 | |
| 91. |
Which of the following refrigerant is highly toxic and flammable? |
| A. | Ammonia |
| B. | Carbon dioxide |
| C. | Sulphur dioxide |
| D. | R-12 |
| Answer» B. Carbon dioxide | |
| 92. |
In order to cool and dehumidify a stream of moist air, it must be passed over the coil at a temperature |
| A. | which lies between the dry bulb and wet bulb temperatures of the incoming stream |
| B. | which lies between the wet bulb and dew point temperatures of the incoming stream |
| C. | which is lower than the dew point temperature of the incoming stream |
| D. | of adiabatic saturation of incoming stream |
| Answer» D. of adiabatic saturation of incoming stream | |
| 93. |
The coefficient of performance of vapour compression refrigeration system is quite __________ as compared to air refrigeration system. |
| A. | low |
| B. | high |
| Answer» C. | |
| 94. |
In order to collect liquid refrigerant and to prevent it from going to a __________ , a device known as accumulator is used at the suction of compressor. |
| A. | compressor |
| B. | condenser |
| C. | expansion valve |
| D. | evaporator |
| Answer» B. condenser | |
| 95. |
Which of the following refrigerant has the lowest boiling point? |
| A. | Ammonia |
| B. | Carbon dioxide |
| C. | Sulphur dioxide |
| D. | R-12 |
| Answer» C. Sulphur dioxide | |
| 96. |
During sensible cooling of air, the relative humidity increases. |
| A. | Yes |
| B. | No |
| Answer» B. No | |
| 97. |
The transfer of heat by molecular collision is known as |
| A. | conduction |
| B. | convection |
| C. | radiation |
| D. | none of these |
| Answer» B. convection | |
| 98. |
In a psychrometric chart, specific humidity (moisture content) lines are |
| A. | vertical and uniformly spaced |
| B. | horizontal and uniformly spaced |
| C. | horizontal and non-uniformly spaced |
| D. | curved lines |
| Answer» C. horizontal and non-uniformly spaced | |
| 99. |
The expression = ρ is called |
| A. | Fourier equation |
| B. | Stefan-Boltzmann equation |
| C. | Newton-Rikhmann equation |
| D. | Joseph-Stefan equation |
| Answer» C. Newton-Rikhmann equation | |
| 100. |
An evaporator is also known as |
| A. | freezing coil |
| B. | cooling coil |
| C. | chilling coil |
| D. | all of these |
| Answer» E. | |