Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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

Thermostatic valve

Electrically operated throttling valve

Capillary tube

Manually operated valve

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

High pressure side close to receiver

Low pressure side near receiver

Suction of compressor

Delivery of compressor

3. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

4. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Wet bulb temperature

Relative humidity

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

56 bars

Slightly above atmospheric pressure

24 bars

Atmospheric pressure

6. During humidification process, dry bulb temperature

Increases

None of these

Decreases

Remains constant

7. The fluids used in Electrolux refrigerator are

Water and hydrogen

None of these

Ammonia, water and hydrogen

Ammonia and hydrogen

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

Large displacements and high condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

9. Which of the following statement is correct?

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

All of these

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

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

10. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Quiet operation

Very little power consumption

Noisy operation

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11. Pick up the incorrect statement

Lithium bromide plant can't operate below 0°C

Lithium bromide used in vapour absorption cycle is non volatile

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

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

12. Absorption system normally uses the following refrigerant

Freon-11

Ammonia

Freon-22

CO2

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

Humidification

Cooling and dehumidification

Dehumidification

Heating and humidification

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

Red

Yellow

Orange

Bright green

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

None of these

Wet bulb temperature

Dry bulb temperature

Dew point temperature

16. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

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

Remain same

Increases

Depends on other factors

Decreases

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

After passing through the condenser

After passing through the expansion throttle valve

Before passing through the condenser

Before entering the expansion valve

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

Zero

0.5

1.0

0.75

20. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

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

All of these

CO₂

R-12

Ammonia

22. During sensible heating of air _________ decreases.

Wet bulb temperature

Specific humidity

Relative humidity

Dry bulb temperature

23. During dehumidification process, the relative humidity

Remains constant

Decreases

None of these

Increases

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

Halide torch which on detection produces greenish flame lighting

Sulphur sticks which on detection gives white smoke

Using reagents

Smelling

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

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

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

Smaller cabinet should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

Perfectly tight vapour seal should be used

27. The moisture in a refrigerant is removed by

Dehumidifier

Evaporator

Safety relief valve

Driers

28. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

29. 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

Relative humidity

Absolute humidity

Humidity ratio

Degree of saturation

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

Condenser

Expansion valve

Compressor

Evaporator

Page 4 of 4

31. During humidification process, __________ increases.

Specific humidity

Wet bulb temperature

Dry bulb temperature

Relative humidity

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

Less

Same

More/less depending on size of plant

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

Dry vapour

High pressure saturated liquid

Wet vapour

Very wet vapour

34. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ hr

80 kcal/ hr

50 kcal/ min

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

None of these

Lower

Higher

Same

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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

Zero

100

38. Which of the following statement is wrong?

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

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

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.

39. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

Two cooling turbines and one heat exchanger

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

Compressor

Condenser

Expansion valve

Evaporator

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Refrigeration & Air-Conditioning Practice Set-1

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