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Heat Transfer, Refrigeration and Air Conditioning MCQ Questions & Answers

Heat Transfer, Refrigeration and Air Conditioning MCQs : This section focuses on the "Heat Transfer, Refrigeration and Air Conditioning". These Multiple Choice Questions (MCQs) should be practiced to improve the Heat Transfer, Refrigeration and Air Conditioning skills required for various interviews (campus interview, walk-in interview, company interview), placement, entrance exam and other competitive examinations.




Question 1

The difference between dry bulb temperature and wet bulb temperature, is called

A. dry bulb depression
B. wet bulb depression
C. dew point depression
D. degree of saturation

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Question 2

The process of heat transfer from a hot body to a cold body, in a straight line, without affecting the intervening medium, is called radiation.

A. TRUE
B. FALSE

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Question 3

The temperature of ammonia after compression in a vapour compression system is

A. 20 to 50° C
B. 50 to 70° C
C. 70 to 110° C
D. none of these

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Question 4

Which of the following statement is wrong?

A. The heat transfer in liquid and gases takes place according to convection.
B. The amount of heat flow through a body is dependent upon the material of the body.
C. The thermal conductivity of solid metals increases with rise in temperature,
D. Logarithmic mean temperature difference is not equal to the arithmetic mean temperature difference.

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Question 5

The formation of frost on cooling coils in a refrigerator

A. increases heat transfer
B. improves C.O.P. of the system
C. increases power consumption
D. reduces power consumption

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Question 6

During a refrigeration cycle, heat is rejected by the refrigerant in a

A. compressor
B. condenser
C. evaporator
D. expansion valve

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Question 7

A water cooled condenser operates at a __________ condensing temperature than an air-cooled condenser.

A. higher
B. lower

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Question 8

Defrosting of a refrigerator may be done by stopping the compressor for a short period.

A. Correct
B. Incorrect

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Question 9

According to Dalton's law of partial pressures, (where pb = Barometric pressure, pa = Partial pressure of dry air, and pv = Partial pressure of water vapour)

A. Pb = pa - pv
B. Pb = pa + pv
C. Pb = pa x pv
D. Pb = pa/pv

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Question 10

In case of solids, the heat transfer takes place according to radiation.

A. Correct
B. Incorrect

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Question 11

The condition of refrigerant after leaving the compressor and before entering the condenser is superheated vapour.

A. Yes
B. No

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Question 12

During sensible cooling of air __________ decreases.

A. wet bulb temperature
B. relative humidity
C. dry bulb temperature
D. specific humidity

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Question 13

Thermal diffusivity is a

A. function of temperature
B. physical property of a substance
C. dimensionless parameter
D. all of these

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Question 14

A perfect black body is one which

A. is black in colour
B. absorbs heat radiations of all wave lengths falling on it
C. reflects all the heat radiations
D. transmits the heat radiations

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Question 15

The by-pass factor for a cooling coil

A. increases with increase in velocity of air passing through it
B. decreases with increase in velocity of air passing through it
C. remains unchanged with increase in velocity of air passing through it
D. may increase or decrease with increase in velocity of air passing through it depending upon the condition of air entering

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Question 16

While designing the refrigeration system of an aircraft, the prime consideration is that the

A. system has high C.O.P.
B. power per TR is low
C. mass of refrigerant circulated in the system is low
D. mass of the refrigeration equipment is low

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Question 17

The amount of radiation mainly depends upon the

A. nature of the body
B. temperature of the body
C. type of surface of the body
D. all of these

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Question 18

The coefficient of performance of Heat Pump is always __________ one.

A. equal to
B. less than
C. greater than

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Question 19

In aqua-ammonia and Lithium-bromide water absorption refrigeration systems, the refrigerants are respectively

A. water and water
B. water and lithium bromide
C. ammonia and lithium bromide
D. ammonia and water

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Question 20

The wet bulb temperature during sensible heating of air

A. remains constant
B. increases
C. decreases

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Question 21

The relative humidity decreases as air gets wet.

A. TRUE
B. FALSE

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Question 22

The heat transfer takes place according to

A. Zeroth law of thermodynamics
B. First law of thermodynamics
C. Second law of thermodynamics
D. Kirchhoff's law

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Question 23

The heat transfer by conduction through a thick sphere is same as through a thick cylinder.

A. TRUE
B. FALSE

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Question 24

As relative humidity decreases, the dew point temperature will be __________ wet bulb temperature.

A. same as
B. lower than
C. higher man

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Question 25

In free convection heat transfer transition from laminar to turbulent flow is governed by the critical value of the

A. Reynold's number
B. Grashoff's number
C. Reynold's number, Grashoff's number
D. Prandtl number, Grashoff's number

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Question 26

An electrolux refrigerator is called a __________ absorption system.

A. single fluid
B. two fluids
C. three fluids

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Question 27

The heat transfer by radiation __________ a medium.

A. requires
B. does not require

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Question 28

The total radiation from a black body per second per unit area is __________ fourth power of the absolute temperature. This statement is known as Stefan-Boltzmann law.

A. equal to
B. directly proportional to
C. inversely proportional to

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Question 29

The humidity ratio or specific humidity is the mass of water vapour present in

A. 1 m3 of wet air
B. 1 m3 of dry air
C. 1 kg of wet air
D. 1 kg of dry air

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Question 30

The wet bulb temperature lines, on the psychrometric chart, are curved lines.

A. TRUE
B. FALSE

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Question 31

The subcooling in a refrigeration cycle

A. does not alter C.O.P.
B. increases C.O.P.
C. decreases C.O.P.
D. none of these

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Question 32

For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of

A. copper
B. aluminium
C. steel
D. brass

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Question 33

In a refrigerating machine, heat rejected is __________ heat absorbed.

A. equal to
B. less than
C. greater than

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Question 34

In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be

A. 0.3
B. 0.6
C. 0.67
D. 1.5

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Question 35

The optimum effective temperature for human comfort is

A. higher in winter than in summer
B. lower in winter than in summer
C. same in winter and summer
D. not dependent on season

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Question 36

A refrigeration system

A. removes heat from a low temperature body and delivers it to a high temperature body
B. removes heat from a high temperature body and delivers it to a low temperature body
C. rejects energy to a low temperature body
D. none of the above

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Question 37

The highest thermal diffusivity is of

A. iron
B. lead
C. concrete
D. wood

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Question 38

Thermal conductivity of water __________ with rise in temperature.

A. remains same
B. decreases
C. increases
D. may increase or decrease depending upon temperature

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Question 39

The relative humidity is defined as

A. the mass of water vapour present in 1 m3 of dry air
B. the mass of water vapour present in 1 kg of dry air
C. the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.
D. the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

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Question 40

Degree of saturation or percentage humidity is

A. the mass of water vapour present in 1 m3 of dry air
B. the mass of water vapour present in 1 kg of dry air
C. the ratio of the actual mass of water vapour in a unit mass of dry air to the mass of water vapour in the same mass of dry air when it is saturated at the same temperature and pressure.
D. the ratio of actual mass of water vapour in a given volume of moist air to the mass of water vapour in the same volume of saturated air at the same temperature and pressure

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Question 41

During adiabatic saturation process on unsaturated air __________ remains constant.

A. relative humidity
B. dew point temperature
C. dry bulb temperature
D. wet bulb temperature

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Question 42

The thickness of thermal and hydrodynamic boundary layer is equal if Prandtl number is

A. equal to one
B. greater than one
C. less than one
D. equal to Nusselt number

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Question 43

The critical radius is the insulation radius at which the resistance to heat flow is

A. maximum
B. minimum
C. zero
D. none of these

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