Refrigeration & Air-Conditioning Practice Set-1

Page 1 of 4

1. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Equal to atmospheric pressure

Could be anything

Higher than atmospheric pressure

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

CO₂

All of these

R-12

Ammonia

3. The refrigerant widely used in domestic refrigerators is

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

24 bars

56 bars

Slightly above atmospheric pressure

Atmospheric pressure

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

Same

None of these

Lower

Higher

6. During sensible cooling of air ________ decreases.

Relative humidity

Specific humidity

Wet bulb temperature

Dry bulb temperature

7. During humidification process, dry bulb temperature

Decreases

None of these

Remains constant

Increases

8. Which of the following statement is correct?

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

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.

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

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

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

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

Smelling

Halide torch which on detection produces greenish flame lighting

Using reagents

Sulphur sticks which on detection gives white smoke

Page 2 of 4

11. The reduced ambient air cooling system has

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and two heat exchangers

Two cooling turbines and one heat exchanger

12. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

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

0.75

0.5

1.0

Zero

14. The moisture in a refrigerant is removed by

Evaporator

Dehumidifier

Safety relief valve

Driers

15. 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

Relative humidity

Humidity ratio

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

High pressure side close to receiver

Delivery of compressor

Suction of compressor

Low pressure side near receiver

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

Evaporator

Expansion valve

Condenser

Compressor

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

Same

More

Less

More/less depending on size of plant

19. 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

20. During dehumidification process, the relative humidity

None of these

Remains constant

Increases

Decreases

Page 3 of 4

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

20

50

100

Zero

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

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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

Dry vapour

Very wet vapour

Wet vapour

High pressure saturated liquid

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

Humidification

Dehumidification

Cooling and dehumidification

Heating and humidification

25. The fluids used in Electrolux refrigerator are

Water and hydrogen

Ammonia and hydrogen

None of these

Ammonia, water and hydrogen

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

Before passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

After passing through the condenser

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

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

Decreases

Remain same

Depends on other factors

Increases

29. Which of the following statement is wrong?

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.

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

30. An important characteristic of absorption system of refrigeration is

Very little power consumption

Quiet operation

Noisy operation

Cooling below 0°C

Page 4 of 4

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

Condenser

Expansion valve

Evaporator

Compressor

32. Absorption system normally uses the following refrigerant

Freon-11

CO2

Freon-22

Ammonia

33. 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

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

Bright green

Yellow

Red

Orange

35. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ min

80 kcal/ hr

50 kcal/ hr

36. During humidification process, __________ increases.

Wet bulb temperature

Relative humidity

Dry bulb temperature

Specific humidity

37. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

Lithium bromide plant can't operate below 0°C

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

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

38. During sensible heating of air _________ decreases.

Dry bulb temperature

Specific humidity

Wet bulb temperature

Relative humidity

39. 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

Smaller cabinet should be used

Perfectly tight vapour seal should be used

Bigger cabinet should be used

40. Under cooling in a refrigeration cycle

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Refrigeration & Air-Conditioning Practice Set-1

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