Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. In a domestic vapour compression refrigerator, the refrigerant commonly used is

R-12

CO₂

All of these

Ammonia

2. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

3. In vapour compression cycle, the condition of refrigerant is saturated liquid

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

After passing through the expansion throttle valve

4. The leaks in a refrigeration system using Freon are detected by

Sulphur sticks which on detection gives white smoke

Using reagents

Smelling

Halide torch which on detection produces greenish flame lighting

5. 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, is called

Absolute humidity

Degree of saturation

Humidity ratio

Relative humidity

6. The COP of a vapour compression plant in comparison to vapour absorption plant is

Less

More/less depending on size of plant

Same

7. Which of the following statement is correct?

All of these

In vapour absorption refrigerator, the compression of refrigerant is avoided.

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.

8. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

Smaller cabinet should be used

Perfectly tight vapour seal should be used

9. During humidification process, __________ increases.

Dry bulb temperature

Specific humidity

Wet bulb temperature

Relative humidity

10. The centrifugal compressors are generally used for refrigerants that require

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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11. In a refrigeration cycle, the flow of refrigerant is controlled by

Condenser

Expansion valve

Compressor

Evaporator

12. Pick up the incorrect statement

A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing

Lithium bromide used in vapour absorption cycle is non volatile

Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

Lithium bromide plant can't operate below 0°C

13. In vapour compression cycle using NH₃ as refrigerant, initial charge is filled at

Delivery of compressor

High pressure side close to receiver

Suction of compressor

Low pressure side near receiver

14. At lower temperatures and pressures, the latent heat of vaporisation of a refrigerant

Increases

Decreases

Remain same

Depends on other factors

15. During sensible heating of air _________ decreases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

16. Absorption system normally uses the following refrigerant

CO2

Ammonia

Freon-22

Freon-11

17. The C.O.P. of a Carnot refrigerator in winter will be _________ as compared to C.O.P. in summer.

Same

Higher

None of these

Lower

18. The colour of the flame of halide torch, in case of leakage of Freon refrigerant, will change to

Red

Bright green

Orange

Yellow

19. The moisture in a refrigerant is removed by

Evaporator

Safety relief valve

Dehumidifier

Driers

20. Which of the following statement is wrong?

The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.

In vapour compression cycle, the useful part of the heat transfer is at the condenser.

The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.

Page 3 of 4

21. In a vapour compression system, the condition of refrigerant before passing through the condenser is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

22. The C.O.P of a refrigeration cycle with increase in evaporator temperature, keeping condenser temperature constant, will

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

23. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

None of these

Ammonia, water and hydrogen

Water and hydrogen

24. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ min

50 kcal/ hr

80 kcal/ min

25. Allowable pressure on high pressure side or ammonia absorption system is of the order of

Slightly above atmospheric pressure

56 bars

Atmospheric pressure

24 bars

26. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

27. During humidification process, dry bulb temperature

Decreases

None of these

Increases

Remains constant

28. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Very little power consumption

Noisy operation

Quiet operation

29. Domestic refrigerator working on vapour compression cycle uses the following type of expansion device

Capillary tube

Electrically operated throttling valve

Manually operated valve

Thermostatic valve

30. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Equal to atmospheric pressure

Could be anything

Higher than atmospheric pressure

Page 4 of 4

31. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

Dew point temperature

None of these

Dry bulb temperature

Wet bulb temperature

32. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

33. The condition of refrigerant after passing through the expansion or throttle valve, in a vapour compression system is

Dry vapour

Wet vapour

Very wet vapour

High pressure saturated liquid

34. The wet bulb depression is zero when relative humidity is

1.0

Zero

0.75

0.5

35. During dehumidification process, the relative humidity

Increases

Remains constant

Decreases

None of these

36. The process, generally used in winter air-conditioning to warm and humidity the air, is called

Dehumidification

Humidification

Heating and humidification

Cooling and dehumidification

37. For air conditioning the operation theater in a hospital, the percentage of outside air in the air supplied is

100

Zero

38. During sensible cooling of air ________ decreases.

Wet bulb temperature

Specific humidity

Relative humidity

Dry bulb temperature

39. Where does the lowest temperature occur in a vapour compression cycle?

Condenser

Expansion valve

Evaporator

Compressor

40. The refrigerant widely used in domestic refrigerators is

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

Refrigeration & Air-Conditioning Practice Set-1

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