Refrigeration & Air-Conditioning Practice Set-1

Page 1 of 4

1. During dehumidification process, the relative humidity

Increases

Remains constant

None of these

Decreases

2. Which of the following statement is wrong?

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

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

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

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

3. Which of the following statement is correct?

All of these

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

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.

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

Red

Yellow

Orange

Bright green

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

Condenser

Evaporator

Expansion valve

Compressor

6. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Wet bulb temperature

Specific humidity

7. The refrigerant widely used in domestic refrigerators is

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

Increases

Depends on other factors

Decreases

Remain same

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

0.75

Zero

1.0

0.5

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

Condenser

Expansion valve

Compressor

Evaporator

Page 2 of 4

11. Under cooling in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

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

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Using reagents

Smelling

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

100

50

20

Zero

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

Less

More/less depending on size of plant

Same

More

15. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Evaporator

Dehumidifier

16. An important characteristic of absorption system of refrigeration is

Quiet operation

Cooling below 0°C

Noisy operation

Very little power consumption

17. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

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

Very wet vapour

Dry vapour

High pressure saturated liquid

Wet vapour

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

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

Atmospheric pressure

56 bars

Slightly above atmospheric pressure

24 bars

Page 3 of 4

21. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

Could be anything

22. 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

Degree of saturation

Humidity ratio

Relative humidity

Absolute humidity

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

Higher

None of these

Lower

Same

24. During humidification process, __________ increases.

Specific humidity

Relative humidity

Dry bulb temperature

Wet bulb temperature

25. Absorption system normally uses the following refrigerant

Ammonia

Freon-11

Freon-22

CO2

26. 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

27. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Relative humidity

Wet bulb temperature

28. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

29. During humidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

30. 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

Page 4 of 4

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

Heating and humidification

Humidification

Cooling and dehumidification

Dehumidification

32. 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

Perfectly tight vapour seal should be used

Bigger cabinet should be used

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

Electrically operated throttling valve

Manually operated valve

Capillary tube

Thermostatic valve

34. 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

Wet bulb temperature

Dry bulb temperature

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

Delivery of compressor

High pressure side close to receiver

Low pressure side near receiver

Suction of compressor

36. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Ammonia, water and hydrogen

None of these

Water and hydrogen

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

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

38. One ton refrigeration corresponds to

80 kcal/ hr

80 kcal/ min

50 kcal/ min

50 kcal/ hr

39. Pick up the incorrect statement

Lithium bromide plant can't operate below 0°C

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

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

CO₂

R-12

Ammonia

All of these

Refrigeration & Air-Conditioning Practice Set-1

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