Refrigeration & Air-Conditioning Practice Set-1

Page 1 of 4

1. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Higher than atmospheric pressure

Could be anything

Equal to atmospheric pressure

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

Ammonia

CO₂

R-12

All of these

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

Smelling

Sulphur sticks which on detection gives white smoke

Using reagents

Halide torch which on detection produces greenish flame lighting

4. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Dry vapour

Wet vapour

High pressure saturated liquid

Very wet vapour

6. Under cooling in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

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

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

8. Absorption system normally uses the following refrigerant

CO2

Freon-11

Ammonia

Freon-22

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

High pressure side close to receiver

Suction of compressor

Delivery of compressor

Low pressure side near receiver

10. Which of the following statement is wrong?

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

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.

Page 2 of 4

11. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

13. 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

Humidity ratio

Degree of saturation

Relative humidity

Absolute humidity

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

Manually operated valve

Thermostatic valve

Capillary tube

Electrically operated throttling valve

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

Slightly above atmospheric pressure

24 bars

Atmospheric pressure

56 bars

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

Humidification

Dehumidification

Cooling and dehumidification

Heating and humidification

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

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

18. During sensible heating of air _________ decreases.

Specific humidity

Wet bulb temperature

Dry bulb temperature

Relative humidity

19. An important characteristic of absorption system of refrigeration is

Very little power consumption

Quiet operation

Cooling below 0°C

Noisy operation

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

More

Less

More/less depending on size of plant

Same

Page 3 of 4

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

Lower

None of these

Higher

Same

22. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Evaporator

Dehumidifier

23. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Ammonia, water and hydrogen

None of these

Water and hydrogen

24. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

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

Perfectly tight vapour seal should be used

Smaller cabinet should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

26. During dehumidification process, the relative humidity

Remains constant

Increases

Decreases

None of these

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

Expansion valve

Evaporator

Condenser

Compressor

28. During humidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

29. Pick up the incorrect statement

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

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

Lithium bromide plant can't operate below 0°C

30. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

Page 4 of 4

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

Zero

0.5

0.75

1.0

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

Bright green

Yellow

Orange

Red

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

Increases

Remain same

Decreases

Depends on other factors

34. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ hr

50 kcal/ min

80 kcal/ min

35. 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

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

Dry bulb temperature

Wet bulb temperature

None of these

Dew point temperature

37. 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 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.

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

Evaporator

Expansion valve

Compressor

Condenser

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

50

20

100

Zero

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

After passing through the expansion throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

Refrigeration & Air-Conditioning Practice Set-1

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