Refrigeration & Air-Conditioning Practice Set-1

Page 1 of 4

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

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

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

Sulphur sticks which on detection gives white smoke

Smelling

Halide torch which on detection produces greenish flame lighting

Using reagents

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

Perfectly tight vapour seal should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

4. 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

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

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

After passing through the expansion throttle valve

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

Same

More/less depending on size of plant

Less

More

7. The moisture in a refrigerant is removed by

Dehumidifier

Evaporator

Driers

Safety relief valve

8. During sensible heating of air _________ decreases.

Specific humidity

Dry bulb temperature

Relative humidity

Wet bulb temperature

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

Orange

Red

Bright green

Yellow

10. During sensible cooling of air ________ decreases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

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

Suction of compressor

Delivery of compressor

High pressure side close to receiver

Low pressure side near receiver

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

Dew point temperature

Wet bulb temperature

None of these

Dry bulb temperature

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

Lower

Same

Higher

None of these

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

Condenser

Expansion valve

Evaporator

Compressor

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

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

Capillary tube

Electrically operated throttling valve

Thermostatic valve

Manually operated valve

18. An important characteristic of absorption system of refrigeration is

Very little power consumption

Quiet operation

Noisy operation

Cooling below 0°C

19. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

Heating and humidification

Dehumidification

Cooling and dehumidification

Humidification

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

22. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

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

R-12

Ammonia

All of these

CO₂

24. The reduced ambient air cooling system has

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

25. Which of the following statement is correct?

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.

All of these

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

26. Absorption system normally uses the following refrigerant

Freon-11

CO2

Freon-22

Ammonia

27. The vapour pressure of refrigerant should be

Could be anything

Lower than atmospheric pressure

Higher than atmospheric pressure

Equal to atmospheric pressure

28. During humidification process, __________ increases.

Relative humidity

Wet bulb temperature

Dry bulb temperature

Specific humidity

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

Very wet vapour

Wet vapour

Dry vapour

High pressure saturated liquid

30. The fluids used in Electrolux refrigerator are

None of these

Ammonia and hydrogen

Ammonia, water and hydrogen

Water and hydrogen

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

Depends on other factors

Decreases

Increases

Remain same

32. During dehumidification process, the relative humidity

None of these

Decreases

Remains constant

Increases

33. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

Lithium bromide plant can't operate below 0°C

34. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ hr

80 kcal/ min

50 kcal/ hr

35. During humidification process, dry bulb temperature

None of these

Remains constant

Increases

Decreases

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

Condenser

Expansion valve

Compressor

Evaporator

37. Which of the following statement is wrong?

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.

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

38. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

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

Zero

1.0

0.5

0.75

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

Zero

20

100

50

Refrigeration & Air-Conditioning Practice Set-1

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