COP of vapor compression refrigeration system increases with

Decrease in evaporator temperature at constant condenser temperature

Increase in evaporator temperature at constant condenser temperature

Decrease in evaporator temperature at constant condenser temperature

Increase in condenser temperature at constant evaporator temperature

Increase in mass flow of refrigerant

In vapour compression cycle, the refrigerant exists in a superheated vapour state _____.

after leaving the expansion valve

after passing through the condenser

If the evaporator temperature of a refrigeration plant is lowered, keeping condensing temperature constant, the horse power requirement of compressor will

More or less depending on capacity

In a vapour compression refrigeration system, the high pressure liquid from the condenser / receiver is cooled below its saturation temperature to

Reduce the pressure on the high pressure side

Reduce the net refrigerating effect

Increase the net refrigerating effect

Reduce the pressure on the high pressure side

Lithium bromide is used as an absorbent in ________.

vapour compression refrigeration

vapour absorption refrigeration

In the context of an aircraft refrigeration cycle, what is the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation?

Dry air rated temperature (DART)

One ton refrigeration machine implies that the machine-

Consumes one ton of refrigerant in 24 hours

Has the capacity to convert one ton of water into ice

Is capable of extracting heat that would melt one ton of ice at 0°C into water at 0°C in a period of 24 hours

Consider an ideal vapor compression refrigeration cycle. If the throttling process is replaced by an isentropic expansion process, keeping all the other processes unchanged, which one of the following statements is true for the modified cycle?

Coefficient of performance is lower than that of the original cycle.

Coefficient of performance is higher than that of the original cycle.

Coefficient of performance is lower than that of the original cycle.

Coefficient of performance is the same as that of the original cycle.

Refrigerating effect is lower than that of the original cycle.

Neglecting the pump work, Energy equation for vapor absorption refrigeration system may be written as [where, Q = heat transfer rate into the system]

Qgenerator + Qevaporator + Qcondencer + Qabsorber = 0

Qgenerator + Qevaporator + Qcondencer - Qabsorber = 0

Qgenerator + Qevaporator - Qcondencer + Qabsorber = 0

Qgenerator + Qevaporator - Qcondencer - Qabsorber = 0

An evaporator pressure regulator performs the following function

Maintains compressor inlet pressure

Keeps pressure up for system needs

In a refrigeration system, why are expansion devices located closer to the evaporator?

To ease the flow of the refrigerant

To avoid the flow of the refrigerant

To ease the flow of the refrigerant

On the pressure – enthalpy diagram, condensation and de – superheating is represented by a horizontal line because the process

takes place at constant entropy

takes place constant temperature

takes place at constant pressure

takes place at constant entropy

97 + Mcqs in Refrigeration Cycles And Devices in Mechanical Engineering Page 1 McqOptions

1.	A thermoelectric refrigeration system requires
A.	Low voltage DC input
B.	High voltage DC input
C.	High voltage AC input
D.	Low voltage AC input
Answer» B. High voltage DC input

Discussion

2.	COP of vapor compression refrigeration system increases with
A.	Increase in evaporator temperature at constant condenser temperature
B.	Decrease in evaporator temperature at constant condenser temperature
C.	Increase in condenser temperature at constant evaporator temperature
D.	Increase in mass flow of refrigerant
Answer» B. Decrease in evaporator temperature at constant condenser temperature

Discussion

3.	A refrigerator operates on a reverse Carnot Cycle between 900 K and 300 K. If heat at the rate of 3 kJ/s is extracted from the low-temperature space, then the power required to drive the refrigerator
A.	3 kW
B.	6 kW
C.	9 kW
D.	4 kW
Answer» C. 9 kW

Discussion

4.	Heat is absorbed by a refrigerant during a refrigeration cycle in a-
A.	Condenser
B.	Throttle valve
C.	Evaporator
D.	Compressor
Answer» D. Compressor

Discussion

5.	A house-hold refrigerator works on
A.	vapour absorption cycle
B.	vapour compression cycle
C.	Carrot cycle
D.	Bell-Coleman cycle
Answer» C. Carrot cycle

Discussion

6.	It is proposed to use a heat pump to heat a home in a cold winter, when the surrounding temperature is -23°C to maintain the room at +22°C. If the power rating of the heat pump is 5 kW, the maximum heat transfer rate that can be provided to the home is
A.	11 kW
B.	22 kW
C.	33 kW
D.	44 kW
Answer» D. 44 kW

Discussion

7.	In vapour compression cycle, the refrigerant exists in a superheated vapour state _____.
A.	at the exit of the compressor
B.	after leaving the expansion valve
C.	after leaving the evaporator
D.	after passing through the condenser
Answer» B. after leaving the expansion valve

Discussion

8.	An inventor claims to have developed a refrigeration unit which maintains – 10°C in the refrigerator which is kept in a room where the surrounding temperature is 25°C and which has COP 8.5. His claim is
A.	Valid
B.	Marginally correct
C.	Invalid
D.	None of the above
Answer» D. None of the above

Discussion

9.	A refrigerator is operating on ideal vapour compression cycle with R134a as working fluid atflow rate of 0.1 kg/s Data given are:Enthalpy at the inlet of the compressor = 240 kJ/kgEnthalpy at the outlet of the compressor = 280 kJ/kgEnthalpy at the outlet of the condenser = 100 kJ/kgWhat will be the refrigeration capacity and COP of the refrigerator, respectively?
A.	14 kW, 3.5
B.	4 kW, 4
C.	10 kW, 2
D.	5 kW, 3.5
Answer» B. 4 kW, 4

Discussion

10.	Determine the COP (coefficient of performance) of a heat pump if the rate of heat rejected is 360 kJ/min and power supplied is 2 kW.
A.	3
B.	1
C.	2
D.	4
Answer» B. 1

Discussion

11.	A machine working on a Carnot cycle operates between 305 K and 260 K. Determine the C.O.P. when it is operated as a refrigerating machine.
A.	5.78
B.	6.78
C.	0.147
D.	None of the above
Answer» B. 6.78

Discussion

12.	Ice is formed at 0°C from water at 20°C. The temperature of the brine is - 8°C. The refrigeration cycle used is perfect reversed Carnot cycle. Latent heat of ice = 335 kJ/kg, and cpw = 4.18. The ice formed per kWh will be nearly
A.	81.4 kg
B.	76.4 kg
C.	71.8 kg
D.	68.8 kg
Answer» B. 76.4 kg

Discussion

13.	A heat engine receives heat at the rate of 25 kJ/s and gives an output of 8.2 kW. What will be the thermal efficiency of the heat engine?
A.	67.2%
B.	20.4%
C.	30.4%
D.	32.8%
Answer» E.

Discussion

14.	In Bell-Coleman cycle, the refrigeration effect happens at constant:
A.	enthalpy
B.	volume
C.	entropy
D.	pressure
Answer» E.

Discussion

15.	If the evaporator temperature of a refrigeration plant is lowered, keeping condensing temperature constant, the horse power requirement of compressor will
A.	Remain same
B.	Increase
C.	Decrease
D.	More or less depending on capacity
Answer» C. Decrease

Discussion

16.	In a vapour compression refrigeration system, the high pressure liquid from the condenser / receiver is cooled below its saturation temperature to
A.	Reduce the net work per cycle
B.	Reduce the net refrigerating effect
C.	Increase the net refrigerating effect
D.	Reduce the pressure on the high pressure side
Answer» D. Reduce the pressure on the high pressure side

Discussion

17.	Lithium bromide is used as an absorbent in ________.
A.	vapour compression refrigeration
B.	vapour absorption refrigeration
C.	steam jet refrigeration
D.	Electrolux refrigerators
Answer» C. steam jet refrigeration

Discussion

18.	In the context of an aircraft refrigeration cycle, what is the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation?
A.	Saturated temperature
B.	Dry air rated temperature (DART)
C.	Super-saturated temperature
D.	Dry air temperature (DAT)
Answer» C. Super-saturated temperature

Discussion

19.	If the operating temperatures for a Carnot pump is -3°C and 27°C, then its COP is
A.	8
B.	4
C.	6
D.	10
Answer» E.

Discussion

20.	Consider the following data referring to a refrigerator working on Vapour-compression refrigeration cycle:1. Enthalpy at entry to compressor = 180 kJ/kg2. Enthalpy a exit from compressor = 210 kJ/kg3. Enthalpy at exit of condenser = 60 kJ/kgWhat is the COP of the refrigerator?
A.	2
B.	3
C.	4
D.	5
Answer» D. 5

Discussion

21.	An ideal refrigerator operating between a condenser temperature of 37°C and an evaporator temperature of -3°C, if the machine is functioning as a heat pump, it's coefficient of performance will be
A.	6
B.	6.75
C.	7
D.	7.75
Answer» E.

Discussion

22.	One ton refrigeration machine implies that the machine-
A.	Has a gross weight of 1 ton
B.	Consumes one ton of refrigerant in 24 hours
C.	Has the capacity to convert one ton of water into ice
D.	Is capable of extracting heat that would melt one ton of ice at 0°C into water at 0°C in a period of 24 hours
Answer» E.

Discussion

23.	In a Li-Br water absorption cycle _____ is used as a refrigerant.
A.	water
B.	air
C.	ammonia
D.	lithium-bromide
Answer» B. air

Discussion

24.	A refrigeration plant is designed to work between -3°C and 27°C. The plant works on the Carnot cycle. If the same plant is used as a heat-pump system, then the COP of the heat pump becomes:
A.	10
B.	9
C.	8
D.	7
Answer» B. 9

Discussion

25.	An ideal refrigerator based on reversed Carnot cycle works between – 23°C and +27°C. What will be the required power in kW, if a cooling rate of 1.5 kW is desired?
A.	0.25 kW
B.	0.3 kW
C.	3.25 kW
D.	7.5 kW
Answer» C. 3.25 kW

Discussion

26.	A house requires 60 Mcal/hr in winter for heating. Heat pump absorbs heat from cold air outside and requires 8 Mcal/hr of work. The COP will be
A.	0.75
B.	7.5
C.	6.5
D.	10
Answer» C. 6.5

Discussion

27.	Consider an ideal vapor compression refrigeration cycle. If the throttling process is replaced by an isentropic expansion process, keeping all the other processes unchanged, which one of the following statements is true for the modified cycle?
A.	Coefficient of performance is higher than that of the original cycle.
B.	Coefficient of performance is lower than that of the original cycle.
C.	Coefficient of performance is the same as that of the original cycle.
D.	Refrigerating effect is lower than that of the original cycle.
Answer» B. Coefficient of performance is lower than that of the original cycle.

Discussion

28.	A Freon 12 simple saturation cycle operates at temperature of 35°C and –15°C for the condenser and evaporator. If the refrigeration effect produced by the cycle is 111.5 kJ/kg and the work required by the compressor is 27.2 kJ/kg, the value of COP will be nearly
A.	4.1
B.	3.6
C.	3.1
D.	2.6
Answer» B. 3.6

Discussion

29.	Neglecting the pump work, Energy equation for vapor absorption refrigeration system may be written as [where, Q = heat transfer rate into the system]
A.	Qgenerator + Qevaporator + Qcondencer + Qabsorber = 0
B.	Qgenerator + Qevaporator + Qcondencer - Qabsorber = 0
C.	Qgenerator + Qevaporator - Qcondencer + Qabsorber = 0
D.	Qgenerator + Qevaporator - Qcondencer - Qabsorber = 0
Answer» E.

Discussion

30.	A heat pump works on a reversed Carnot cycle. The temperature in the condenser coils is 27° C and that in the evaporator coils is - 23° C. For a work input of 1 kW, how much is the heat pumped?
A.	1 kW
B.	5 kW
C.	6 kW
D.	None of the above
Answer» D. None of the above

Discussion

31.	A cold storage is to be maintained at - 5°C while the surroundings are at 35°C. The heat leakage from the surroundings into the cold storage is estimated to be 29 kW. The actual COP of the refrigeration plant used is one-third of an ideal plant working between the same temperatures. The power required to drive the plant will be
A.	10 kW
B.	11 kW
C.	12 kW
D.	13 kW
Answer» E.

Discussion

32.	An evaporator pressure regulator performs the following function
A.	Monitors evaporator temp
B.	Maintains compressor inlet pressure
C.	Keeps pressure up for system needs
D.	All of these
Answer» E.

Discussion

33.	One ton of refrigeration is equal to _________ kW.
A.	5
B.	2.5
C.	3.5
D.	1
Answer» D. 1

Discussion

34.	If the COP of a Carnot refrigerator is 6, then the ratio of higher temperature to lower is:
A.	6 : 1
B.	3 : 2
C.	4 : 3
D.	7 : 6
Answer» E.

Discussion

35.	A refrigerator removes heat from a refrigerated space at -5°C at a rate of 0.35 kJ/s and rejects it to an environment at 20°C. The minimum required power input is
A.	30 W
B.	33 W
C.	56 W
D.	124 W
Answer» C. 56 W

Discussion

36.	A refrigerant machine working on reversed Carnot cycle consumes 3 kW for producing the refrigerating effect of 500 kJ/min, for maintaining region at -40°C, the higher temperature of the cycle will be.
A.	317°C
B.	44 K
C.	44°C
D.	233 K
Answer» D. 233 K

Discussion

37.	Identify the incorrect statement, from the following options:Conventionally, in a domestic refrigerator, the coils/tubes at its back ______.
A.	Carry refrigerant fluid
B.	Carry chilled water
C.	Serve as the condenser
D.	Reject heat to the atmosphere
Answer» C. Serve as the condenser

Discussion

38.	In a refrigeration system, why are expansion devices located closer to the evaporator?
A.	To avoid the flow of the refrigerant
B.	To minimise the heat gain
C.	To ease the flow of the refrigerant
D.	To maximise the heat gain
Answer» C. To ease the flow of the refrigerant

Discussion

39.	A refrigerator and heat pump operate between the same temperature limits. If coefficient of performance of the refrigerator is 4, then the coefficient of performance of the pump would be
A.	3
B.	4
C.	5
D.	6
Answer» D. 6

Discussion

40.	In case of a vapor compression refrigerator, if the condenser temperature of the refrigerant is closer to the critical temperature, then there will be1. Excessive power consumption2. High compression3. Large volume flowWhich of the above statements are correct?
A.	1 and 2 only
B.	1 and 3 only
C.	2 and 3 only
D.	1, 2 and 3
Answer» B. 1 and 3 only

Discussion

41.	A Carnot refrigerator requires 1.25 kW per ton of refrigeration to maintain a temperature of 233 K. It higher operating temperature of the cycle
A.	318 K
B.	313 K
C.	315 K
D.	316 K
Answer» E.

Discussion

42.	A refrigerator based on reversed Carnot cycle works between two such temperatures that ratio between low and high temperature is 0.8. what is COP?
A.	2
B.	3
C.	4
D.	5
Answer» D. 5

Discussion

43.	A house requires 60 M cal/hr in winter for heating. Heat pump absorbs heat from cold air outside and requires 8 M cal/hr of work. The COP will be:
A.	0.75
B.	6.5
C.	7.5
D.	15
Answer» D. 15

Discussion

44.	Consider the statements in respect of vapour absorption and vapour compression refrigeration systems.1. The former runs on low-grade energy.2. The pumping work in the former is negligible since the specific volume of the strong liquid solution is small.3. The latter uses an absorber while the former uses a generator.4. The liquid pump alone replaces compressor of the latter.Which of these statements are correct?
A.	1 and 2
B.	1 and 3
C.	1 and 4
D.	2 and 4
Answer» B. 1 and 3

Discussion

45.	Another name for the Bell-Coleman cycle is:
A.	Reversed Carnot cycle
B.	Ideal reverse Brayton cycle
C.	Carnot cycle
D.	Rankine cycle
Answer» C. Carnot cycle

Discussion

46.	A Carnot refrigeration is used to maintain temperature at -30°C that requires 1.28 kW per ton of refrigeration. The heat rejected in kW per tonne refrigeration is:
A.	3.5
B.	2.78
C.	4.78
D.	5.45
Answer» D. 5.45

Discussion

47.	A Carnot engine has an efficiency of 0.5. The COP of refrigerant working with the same temperature limit is
A.	0.5
B.	1
C.	2
D.	1.25
Answer» C. 2

Discussion

48.	On the pressure – enthalpy diagram, condensation and de – superheating is represented by a horizontal line because the process
A.	involve no change in volume
B.	takes place constant temperature
C.	takes place at constant pressure
D.	takes place at constant entropy
Answer» D. takes place at constant entropy

Discussion

49.	A refrigeration plant working on Carnot cycle is designed to take the load of 4 T of refrigeration. The cycle works between 2°C and 27°C. The power required to run the system is:
A.	1.27 kW
B.	3.71 kW
C.	5.71 kW
D.	7.27 kW
Answer» B. 3.71 kW

Discussion

50.	An air refrigeration system works on Bell – Coleman cycle. It draws air at the rate of 1 kg/s from the cold chamber at 1 bar and 5° C. Air is compressed to 7 bar and then is cooled to 25°C before sending it to expansion cylinder. Given γ = 1.4 cp = 1.005 kJ/kg-K and 70.286 = 1.745. Refrigeration effect for this system in tonne per hour, is:
A.	15.8
B.	30.6
C.	3.06
D.	1.58
Answer» C. 3.06

Discussion

Explore topic-wise MCQs in Mechanical Engineering.

A thermoelectric refrigeration system requires

COP of vapor compression refrigeration system increases with

A refrigerator operates on a reverse Carnot Cycle between 900 K and 300 K. If heat at the rate of 3 kJ/s is extracted from the low-temperature space, then the power required to drive the refrigerator

Heat is absorbed by a refrigerant during a refrigeration cycle in a-

A house-hold refrigerator works on

It is proposed to use a heat pump to heat a home in a cold winter, when the surrounding temperature is -23°C to maintain the room at +22°C. If the power rating of the heat pump is 5 kW, the maximum heat transfer rate that can be provided to the home is

In vapour compression cycle, the refrigerant exists in a superheated vapour state _____.

An inventor claims to have developed a refrigeration unit which maintains – 10°C in the refrigerator which is kept in a room where the surrounding temperature is 25°C and which has COP 8.5. His claim is

Determine the COP (coefficient of performance) of a heat pump if the rate of heat rejected is 360 kJ/min and power supplied is 2 kW.

A machine working on a Carnot cycle operates between 305 K and 260 K. Determine the C.O.P. when it is operated as a refrigerating machine.

Ice is formed at 0°C from water at 20°C. The temperature of the brine is - 8°C. The refrigeration cycle used is perfect reversed Carnot cycle. Latent heat of ice = 335 kJ/kg, and cpw = 4.18. The ice formed per kWh will be nearly

A heat engine receives heat at the rate of 25 kJ/s and gives an output of 8.2 kW. What will be the thermal efficiency of the heat engine?

In Bell-Coleman cycle, the refrigeration effect happens at constant:

If the evaporator temperature of a refrigeration plant is lowered, keeping condensing temperature constant, the horse power requirement of compressor will

In a vapour compression refrigeration system, the high pressure liquid from the condenser / receiver is cooled below its saturation temperature to

Lithium bromide is used as an absorbent in ________.

In the context of an aircraft refrigeration cycle, what is the temperature of the air at the exit of the cooling turbine in the absence of moisture condensation?

If the operating temperatures for a Carnot pump is -3°C and 27°C, then its COP is

Consider the following data referring to a refrigerator working on Vapour-compression refrigeration cycle:1. Enthalpy at entry to compressor = 180 kJ/kg2. Enthalpy a exit from compressor = 210 kJ/kg3. Enthalpy at exit of condenser = 60 kJ/kgWhat is the COP of the refrigerator?

An ideal refrigerator operating between a condenser temperature of 37°C and an evaporator temperature of -3°C, if the machine is functioning as a heat pump, it's coefficient of performance will be

One ton refrigeration machine implies that the machine-

In a Li-Br water absorption cycle _____ is used as a refrigerant.

A refrigeration plant is designed to work between -3°C and 27°C. The plant works on the Carnot cycle. If the same plant is used as a heat-pump system, then the COP of the heat pump becomes:

An ideal refrigerator based on reversed Carnot cycle works between – 23°C and +27°C. What will be the required power in kW, if a cooling rate of 1.5 kW is desired?

A house requires 60 Mcal/hr in winter for heating. Heat pump absorbs heat from cold air outside and requires 8 Mcal/hr of work. The COP will be

Consider an ideal vapor compression refrigeration cycle. If the throttling process is replaced by an isentropic expansion process, keeping all the other processes unchanged, which one of the following statements is true for the modified cycle?

A Freon 12 simple saturation cycle operates at temperature of 35°C and –15°C for the condenser and evaporator. If the refrigeration effect produced by the cycle is 111.5 kJ/kg and the work required by the compressor is 27.2 kJ/kg, the value of COP will be nearly

Neglecting the pump work, Energy equation for vapor absorption refrigeration system may be written as [where, Q = heat transfer rate into the system]

A heat pump works on a reversed Carnot cycle. The temperature in the condenser coils is 27° C and that in the evaporator coils is - 23° C. For a work input of 1 kW, how much is the heat pumped?

An evaporator pressure regulator performs the following function

One ton of refrigeration is equal to _________ kW.

If the COP of a Carnot refrigerator is 6, then the ratio of higher temperature to lower is:

A refrigerator removes heat from a refrigerated space at -5°C at a rate of 0.35 kJ/s and rejects it to an environment at 20°C. The minimum required power input is

A refrigerant machine working on reversed Carnot cycle consumes 3 kW for producing the refrigerating effect of 500 kJ/min, for maintaining region at -40°C, the higher temperature of the cycle will be.

Identify the incorrect statement, from the following options:Conventionally, in a domestic refrigerator, the coils/tubes at its back ______.

In a refrigeration system, why are expansion devices located closer to the evaporator?

A refrigerator and heat pump operate between the same temperature limits. If coefficient of performance of the refrigerator is 4, then the coefficient of performance of the pump would be

In case of a vapor compression refrigerator, if the condenser temperature of the refrigerant is closer to the critical temperature, then there will be1. Excessive power consumption2. High compression3. Large volume flowWhich of the above statements are correct?

A Carnot refrigerator requires 1.25 kW per ton of refrigeration to maintain a temperature of 233 K. It higher operating temperature of the cycle

A refrigerator based on reversed Carnot cycle works between two such temperatures that ratio between low and high temperature is 0.8. what is COP?

A house requires 60 M cal/hr in winter for heating. Heat pump absorbs heat from cold air outside and requires 8 M cal/hr of work. The COP will be:

Another name for the Bell-Coleman cycle is:

A Carnot refrigeration is used to maintain temperature at -30°C that requires 1.28 kW per ton of refrigeration. The heat rejected in kW per tonne refrigeration is:

A Carnot engine has an efficiency of 0.5. The COP of refrigerant working with the same temperature limit is

On the pressure – enthalpy diagram, condensation and de – superheating is represented by a horizontal line because the process

A refrigeration plant working on Carnot cycle is designed to take the load of 4 T of refrigeration. The cycle works between 2°C and 27°C. The power required to run the system is: