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
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
Question 2
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
Question 3
A water cooled condenser operates at a __________ condensing temperature than an air-cooled condenser.
A. higher
B. lower
Question 4
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
Question 5
An electrolux refrigerator is called a __________ absorption system.
A. single fluid
B. two fluids
C. three fluids
Question 6
As relative humidity decreases, the dew point temperature will be __________ wet bulb temperature.
A. same as
B. lower than
C. higher man
Question 7
Defrosting of a refrigerator may be done by stopping the compressor for a short period.
A. Correct
B. Incorrect
Question 8
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
Question 9
During a refrigeration cycle, heat is rejected by the refrigerant in a
A. compressor
B. condenser
C. evaporator
D. expansion valve
Question 10
During adiabatic saturation process on unsaturated air __________ remains constant.
A. relative humidity
B. dew point temperature
C. dry bulb temperature
D. wet bulb temperature
Question 11
During sensible cooling of air __________ decreases.
A. wet bulb temperature
B. relative humidity
C. dry bulb temperature
D. specific humidity
Question 12
For ammonia refrigerating systems, the tubes of a shell and tube condenser are made of
A. copper
B. aluminium
C. steel
D. brass
Question 13
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
Question 14
In a refrigerating machine, heat rejected is __________ heat absorbed.
A. equal to
B. less than
C. greater than
Question 15
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
Question 16
In case of solids, the heat transfer takes place according to radiation.
A. Correct
B. Incorrect
Question 17
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
Question 18
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
Question 19
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
Question 20
The coefficient of performance of Heat Pump is always __________ one.
A. equal to
B. less than
C. greater than
Question 21
The condition of refrigerant after leaving the compressor and before entering the condenser is superheated vapour.
A. Yes
B. No
Question 22
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
Question 23
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
Question 24
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
Question 25
The heat transfer by conduction through a thick sphere is same as through a thick cylinder.
A. TRUE
B. FALSE
Question 26
The heat transfer by radiation __________ a medium.
A. requires
B. does not require
Question 27
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
Question 28
The highest thermal diffusivity is of
A. iron
B. lead
C. concrete
D. wood
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
Question 30
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
Question 31
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
Question 32
The relative humidity decreases as air gets wet.
A. TRUE
B. FALSE
Question 33
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
Question 34
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
Question 35
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
Question 36
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
Question 37
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
Question 38
The wet bulb temperature during sensible heating of air
A. remains constant
B. increases
C. decreases
Question 39
The wet bulb temperature lines, on the psychrometric chart, are curved lines.
A. TRUE
B. FALSE
Question 40
Thermal conductivity of water __________ with rise in temperature.
A. remains same
B. decreases
C. increases
D. may increase or decrease depending upon temperature
Question 41
Thermal diffusivity is a
A. function of temperature
B. physical property of a substance
C. dimensionless parameter
D. all of these
Question 42
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.
Question 43
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