Refrigeration & Air-Conditioning Practice Set-1

Page 1 of 4

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

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

2. 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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

3. 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

Bigger cabinet should be used

Refrigerant with lower evaporation temperature should be used

Perfectly tight vapour seal should be used

4. 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

5. During dehumidification process, the relative humidity

Decreases

Increases

Remains constant

None of these

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

Using reagents

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Smelling

7. One ton refrigeration corresponds to

80 kcal/ hr

80 kcal/ min

50 kcal/ min

50 kcal/ hr

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

Evaporator

Condenser

Compressor

Expansion valve

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

Atmospheric pressure

Slightly above atmospheric pressure

56 bars

24 bars

10. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Dry bulb temperature

Specific humidity

Page 2 of 4

11. During humidification process, __________ increases.

Dry bulb temperature

Relative humidity

Wet bulb temperature

Specific humidity

12. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature, pressure and enthalpy

Temperature and enthalpy

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

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

Heating and humidification

Cooling and dehumidification

Humidification

Dehumidification

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

Higher

Lower

None of these

Same

16. The vapour pressure of refrigerant should be

Could be anything

Equal to atmospheric pressure

Lower than atmospheric pressure

Higher than atmospheric pressure

17. Pick up the incorrect statement

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

Lithium bromide plant can't operate below 0°C

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

Yellow

Orange

Red

Bright green

19. The fluids used in Electrolux refrigerator are

None of these

Ammonia, water and hydrogen

Ammonia and hydrogen

Water and hydrogen

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

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

Decrease

Page 3 of 4

21. The refrigerant widely used in domestic refrigerators is

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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

Same

Less

More

More/less depending on size of plant

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

Zero

50

20

100

24. Under cooling in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

25. 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.

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

Condenser

Compressor

Expansion valve

Evaporator

27. An important characteristic of absorption system of refrigeration is

Quiet operation

Noisy operation

Cooling below 0°C

Very little power consumption

28. During humidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

Wet vapour

High pressure saturated liquid

Very wet vapour

Dry vapour

30. Which of the following statement is correct?

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

All of these

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

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

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31. 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 one heat exchanger

Two cooling turbines and two heat exchangers

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

Decreases

Remain same

Depends on other factors

Increases

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

Manually operated valve

Capillary tube

Electrically operated throttling valve

Thermostatic valve

34. 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

Humidity ratio

Relative humidity

Degree of saturation

35. During sensible cooling of air ________ decreases.

Wet bulb temperature

Dry bulb temperature

Specific humidity

Relative humidity

36. The moisture in a refrigerant is removed by

Evaporator

Driers

Dehumidifier

Safety relief valve

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

Zero

0.75

1.0

0.5

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

39. Absorption system normally uses the following refrigerant

Freon-22

Ammonia

CO2

Freon-11

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

CO₂

All of these

R-12

Ammonia

Refrigeration & Air-Conditioning Practice Set-1

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