RAC - Vapour Refrigeration Systems

 VAPOUR REFRIGERATION SYSTEM

1. Heat is absorbed by the refrigerant, during vapour compression refrigeration cycle in

(a) Compressor 

(b) Condenser 

(c) Evaporator 

(d) Throttle valve

 

2. In a simple saturated vapour compression cycle, the refrigerant is in superheated condition

(a) before entering compressor 

(b) before entering condenser

(c) before entering throttle valve 

(d) before entering evaporator

 

3. Sub-cooling is a process of cooling the refrigerant in vapour compression refrigeration system

(a) after compression 

(b) before compression 

(c) before Throttling

(d) none of the above

 

4. The order in which main components of vapour compression refrigeration system are used is

(a) compressor-evaporator-condenser-throttle valve

(b) compressor-condenser-evaporator-throttle valve

(c) compressor-throttle valve- evaporator-condenser

(d) compressor-condenser- throttle valve- evaporator

 

5. The oil separator is incorporated in vapour compression refrigeration system

(a) between evaporator and compressor

(b) between compressor and condenser

(c) between condenser and Throttle valve

(d) between throttle valve and evaporator

 

6. In vapour compression refrigeration cycle the following data is available Heat rejected in condenser 

=65 KW  Work done in compressor = 10 kw, then COP( refrigerator) is

(a) 4.5 

(b) 5.5 

(c) 6.5 

(d) not possible to find with the given data

 

7. Following results are tabulated for vapour compression refrigeration cycle.

Enthalpy at suction = 190 kJ/kg

Enthalpy at discharge from compressor = 210 kJ/kg

Enthalpy at exit from condenser = 80 kJ/kg ,    COP of cycle would be

(a)3.5 

(b) 4.5 

(c) 5.5 

(d) 6.5

 

8. For simple saturated vapour compression refrigeration cycle operating between 5°C and 40°C, and the refrigerants being R-11, R-12, R-717 and R-22, the evaporator pressure is lowest for

(a) R-11 

(b) R-12 

(c) R-717 

(d) R-22

 

9. With reciprocating compressor in vapour compression refrigeration system, wet

compression is not desirable because

(a) liquid trapped up in the head of cylinder may damage the compressor valves

(b) COP of the cycle decreases

(c) volumetric efficiency of compressor decreases

(d) mass flow rate per ton of refrigerant increases

 

10. An ideal refrigerant should have

(a) low latent heat of vaporization

(b) high critical temperature

(c) high boiling point

(d) high specific volume of vapour

 

11. The refrigerant leaving throttle valve is

(a) saturated liquid

(b) saturated vapour

(c) superheated vapour

(d) fraction as saturated vapour and remainder as liquid

 

12. Freon group of refrigerants

(a) toxic 

(b) inflammable 

(c) non-toxic and non-inflammable

(d) highly toxic and inflammable

 

13. The leaks of refrigerant from a cycle may be detected by

(a) halide torch test

(b) sulphur candle test

(c) soap and water test

(d) any of the above

 

14. During compression in a vapour compression cycle the refrigerant is super heated

(a) work done is increased

(b) C.O.P is increased

(c) Work done is reduced

(d) Refrigerating effect is reduced

 

15. Heat is rejected by the refrigerant, during vapour compression refrigeration cycle in

(a) Compressor 

(b) Condenser 

(c) Evaporator 

(d) Throttle valve

 

16. Wet compression vapour compression refrigeration cycle means

(a) Vapour compression takes place in wet region

(b) Vapour compression in dry region, but evaporation in wet region

(c) vapour compression in wet region, but leaves in superheated region

(d) None of the above

RAC - Air Refrigeration Systems

 

AIR REFRIGERATION SYSTEM

1. Reversed carnot cycle comprises

(a) two isentropic processes and two adiabatic processes

(b) two isentropic processes and two isothermal processes

(c) two isentropic processes and two isobaric processes

(d) two isentropic processes and two isochoric processes

 

2. Two Carnot Refrigerators are employed, one for ice making and other for comfort cooling

(a) The COP of the refrigerator for ice making is higher than that for other

(b) The COP of the refrigerator for ice making is same as that for the other

(c) The COP of the refrigerator for ice making is lower than that for other

(d) The COP of Carnot refrigerator will depend on refrigerant used

3. A reversed Carnot cycle has a COP of 4. The ratio of higher temperature to lower temperature will be

(a)  1.25        

(b) 1.5

(c) 2            

(d) 2.5

 

4. Carnot refrigerator absorbs heat at -13° C and requires 1 kW for each 6.5 kW of heat absorbed, the COP and temperature of heat rejections respectively

(a) COP = 6.5, t = 27° C     

(b) COP = 7.5, t = 27° C

(c) COP = 6.5, t = 30° C     

(d) COP = 7.5, t = 37° C

 

5. The dense air refrigeration system as compared to open air refrigeration system for same range of temperatures using Bell- Colemann cycle requires.

(a) Same power/Ton of Refrigeration

(b) Lower power/Ton of Refrigeration

(c) Higher power/Ton of Refrigeration

(d) Unpredictable Results

 

6. The amount of heat absorbed by the system at low temperature is

(a) COP

(b) refrigerating effect

(c) work done on the system

(d) refrigeration efficiency

 

7. No refrigerator using reversed Carnot cycle has been constructed because

(a) it is less efficient

(b) it is uneconomical

(c) isentropic portions of cycle require low speeds where as isothermal portions require high speeds

(d) isentropic portions of cycle require high speeds where as isothermal portions require low speeds

 

8. A refrigeration cycle is usually a

(a) open cycle 

(b) closed cycle 

(c) mixed cycle 

(d) Hybrid cycle

 

9. Co-efficient of performance of a Reversed Carnot cycle refrigerator working between higher temperature T2 and lower temperature T1

(a) will increase with increase in T1 keeping T2 fixed

(b) will decrease with increase in T1 keeping T2 fixed

(c) will first increase with increase in T1 and then decrease with increase T1 keeping T2 fixed

(d) None of the above

 

10.Bell-Colemann cycle comprises

(a) two isentropic processes and two adiabatic processes

(b) two isentropic processes and two isothermal processes

(c) two isentropic processes and two isobaric processes

(d) two isentropic processes and two isochoric processes

 

11. The COP of Carnot Refrigerator is 3 and it produces 1 TR. The work that will be done is equal to

(a)  70 kJ/min 

(b) 100 kJ/min 

(c) 200 kJ/min 

(d) 210 kJ/min

 

12. In Bell – Colemann refrigerator for the same temperature range

(a) COP of dense air system is equal to COP of open air system

(b) COP of dense air system is lower than COP of open air system

(c) COP of dense air system is higher than COP of open air system

(d) COP of dense air system may be higher or lower than COP of open air system depending upon  pressure ratio.

 

13. For very high speed planes cruising at Mach number 2.5 and above, the air craft refrigeration system recommended is

(a) Simple evaporative type 

(b) Boot-strap type

(c) Regenerative type 

(d) Boot strap evaporative type

 

14. The air craft system giving Lowest Dry Air Rated Turbine discharge temperature at supersonic cruising speeds of the plane, is

(a) Reduced ambient system of Refrigeration

(b) Boot-strap system of Refrigeration

(c) Regenerative system of Refrigeration

(d) Boot strap evaporative system of Refrigeration

 

15. There are two cooling turbines in

(a) Reduced ambient system of Refrigeration

(b) Boot-strap system of Refrigeration

(c) Regenerative system of Refrigeration

(d) Boot strap evaporative system of Refrigeration

 

16. There are two stages of compression of air in

(a) Reduced ambient system of Refrigeration

(b) Boot-strap system of Refrigeration

(c) Regenerative system of Refrigeration

(d) Simple evaporative system of Refrigeration

 

17. A Bell-Colemann cycle is

(a) reversed Carnot Cycle

(b) reversed Joule Cycle

(c) reversed Rankine cycle

(d) None of the above

 

18. In a refrigeration cycle the heat is rejected by refrigerant at

(a) expansion valve

(b) compressor

(c) condenser

(d) all the above

 

19. A reversible refrigerator working between two fixed temperatures

(a) has the same COP whatever the working substance

(b) has its COP increased for working substance with high enthalpy of evaporation

(c) has its COP increased for working substance with higher specific heats

(d) none of the above

MCQ-Refrigeration and Airconditioning

 MCQ-Refrigeration and Airconditioning

1-During which component of vapour compression refrigeration system, the enthalpy remains constant:

(A) Evaporator

(B) Compressor

(C) Throttle valve

(D) None

 

2-Which one of the following is a CFC refrigerant?

(A) R 744

(B) R 290

(C) R 502

(D) R 718

 

3-In sensible cooling process the relative humidity:

(A) decreases

(B) increases

(C) remains constant

(D) none of the above

 

4-In psychrometric chart, dew point temperature lines are

(A) horizontal

(B) vertical

(C) curved

(D) straight lines slopping downwards to the right

 

5-In psychrometric chart, specific humidity lines are:

(A) vertical

(B) horizontal

(C) inclined

(D) curved lines

 ANSWERS: 1-(C), 2-(C), 3-(B), 4-(A), 5-(B)

6-Commonly used refrigerant in commercial ice plant is

(A) CO₂

(B) Freon 12

(C) Ammonia

(D) Air

 

7-Accumulator is provided for

(A) Storing of liquid refrigerant

(B) exchange of heat

(C) storing of unvaporized liquid

(D) condensing gas

 

8-Oil separator if fitted in between

(A) Condenser and evaporator

(B) On the suction line

(C) compressor and condenser

(D) at the receiver outlet

 

9-An air washer can work as:

(A) Humidifier

(B) Dehumidifier

(C) Filter

(D) All of the above

 

10-Sling psychrometer is used to measure

(A) only dry bulb temperature

(B) only wet bulb temperature

(C) dry and wet bulb temperature

(D) relative humidity

 

ANSWERS:  6-(C), 7-(A), 8-(C), 9-(D), 10-(C)

11-Latent heat of fusion of ice is:
(A) 335 kJ/kg

(B) 144 BTU/lb

(C) 80 kilo-calorie/kg

(D) all of the above

 

12-Select the wrong characteristics of refrigerant:

(A) low latent heat

(B) low boiling point

(C) high thermal conductivity

(D) none of the above

 

13-Sensible heat factor is:

(A) Sensible heat/Latent heat

(B) Total heat/Sensible heat

(C) Latent heat/Sensible heat

(D) Sensible heat/Total heat

 

14-The function of duct in air conditioning unit is:

(A) air cooling

(B) air cleaning

(C) air drying

(D) air distribution

 

15-Process of changing solid into vapour state without passing through liquid state is:

(A) super heating

(B) sublimation

(C) subcooling

(D) triple point

 

ANSWERS: 11-(A), 12-(A), 13-(D), 14-(D), 15-(B)

16-Amount of heat required to raise the temperature of one unit of substance through 1 degree is called:

(A) C.H.U.

(B) B.T.U.

(C) Calorie

(D) Specific heat

 

17-The COP of a domestic air conditioning in comparison to domestic refrigerator will be:

(A) same

(B) less

(C) more

(D) depends upon weather conditions

 

18-Solenoid valve is operated:

(A) electrically

(B) by hand

(C) by gas pressure

(D) by oil pressure

 

19-Subcooling is a process of cooling the refrigerant in vapour compression refrigeration system before:

(A) evaporation

(B) throttling

(C) condensation

(D) compression

 

20-Pump down the system for:

(A) more cooling effect

(B) to check compressor efficiency

(C) gas charging

(D) to attend maintenance in low side

 

ANSWERS: 16-(D), 17-(C), 18-(A), 19-(B), 20-(D)

 

21-The process in winter air conditioning is

(A) Dehumidification

(B) Heating and humidification

(C) Humidification

(D) Cooling and dehumidification

 

22-A thermostatic expansion valve function with

(A) suction pressure

(B) discharge pressure

(C) discharge temperature

(D) suction temperature

 

23-The colour of the flame of halide torch in case of leakage of Freon refrigerant will change t:

(A) Purple

(B) Pink

(C) Bright green

(D) Blue

 

24-Liquid charged in thermostatic expansion valves sensing bulb is:

(A) alcohol

(B) same refrigerant

(C) mercury

(D) nitrogen

 

25-The oil used with 134A refrigerant is:

(A) Mineral oil

(B) Capilla D

(C) Polyol ester oil

(D) Lubricating oil

ANSWERS: 21-(B), 22-(A), 23-(C), 24-(B), 25-(C)

26-The difference between DBT and WBT is called:

(A) wet bulb depression

(B) dew point depression

(C) effective temperature

(D) adiabatic saturation temperature

 

27-A device which is used to find relative humidity:

(A) Pyrometer

(B) Anemometer

(C) Hydrometer

(D) Hygrometer

 

28-Which type of valve is used in a reciprocating refrigeration compressor?

(A) rotary valve

(B) poppet valve

(C) ring plate

(D) glob valve

29-The capacity of visible cooler is expressed in:

(A) cubic feet

(B) litres

(C) k.cal/TR

(D) tons of refrigeration

 

30-Chemical name of Freon 22 is

(A) Dichlorodifluoro methane

(B) Monochlorodifluoro methane

(C) Trichloromonofluoro methane

(D) Dichloromonofluoro methane

 

ANSWERS: 26-(A), 27-(D), 28-(B), 29-(B), 30-(B)

 

 

31-The operation theatre in a hospital is to be air conditioned. Suggest the percentage of outside air being circulated in the theatre:

(A) zero

(B) 20

(C) 50

(D) 100

 

32-Which of the following refrigerant has the lowest boiling point?

(A) carbon dioxide

(B) Ammonia

(C) Hydrogen

(D) Freon 12

 

33-Auto defrost is operated by

(A) Evaporator fan

(B) Thermostat

(C) Timer watch

(D) Heating element

 

34-The absolute zero temperature corresponds on the condition when

(A) all the substances exit only as solids

(B) volume of a gas reduces to zero

(C) kinetic energy of gas molecules becomes zero

(D) no pressure is exerted by the gas

 

35-Sum of atmospheric pressure and gauge pressure is called

(A) Total pressure

(B) Absolute pressure

(C) Normal pressure

(D) Natural pressure

 ANSWERS: 31-(D), 32-(C), 33-(A), 34-(C), 35-(B)

36-The effectiveness of the cooling tower is dependent on:

(A) dry bulb temperature of the air

(B) direction of the flow of air

(C) wet bulb temperature of the air

(D) none of the above

 

37-One micron of vaccum is equal to

(A) 0.1 MM Hg

(B) 0.01 MM Hg

(C) 0.001 MM Hg

(D) 0.0001 MM Hg

 

38-In a flooded evaporator which of the following types of expansion device is employed?

(A) float valve

(B) capillary tube

(C) automatic expansion valve

(D) thermostatic expansion valve

 

39-In a thermal electric expansion valve which senses the suction temperature is

(A) Transformer

(B) Thermister

(C) Thermostat

(D) Rheostat

 

40-The specific humidity is the mass of water vapour present in

(A) 1 kg of dry air

(B) 1 m³ of dry air

(C) 1 m³ of wet air

(D) 1 kg of wet air

 

ANSWERS: 36-(C), 37-(C), 38-(A), 39-(B), 40-(A)

 

Ref: https://scholarexpress.com/multiple-choice-questions-mcq-answers-refrigeration-air-conditioning/

Composed By:      
R.Satheesh, M.E., Asso.Prof.,