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

Small displacements and high condensing pressures

Large displacements and low condensing pressures

2. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

3. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

None of these

Ammonia and hydrogen

Water and hydrogen

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

24 bars

Slightly above atmospheric pressure

Atmospheric pressure

56 bars

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

R-12

CO₂

Ammonia

All of these

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

Very wet vapour

High pressure saturated liquid

Wet vapour

Dry vapour

7. 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

8. 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.

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

Orange

Red

Yellow

Bright green

10. 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

Bigger cabinet should be used

Perfectly tight vapour seal should be used

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11. 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

Smelling

Using reagents

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

0.75

1.0

0.5

Zero

13. Under cooling in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

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

Evaporator

Compressor

Condenser

Expansion valve

15. During humidification process, dry bulb temperature

None of these

Decreases

Increases

Remains constant

16. The vapour pressure of refrigerant should be

Could be anything

Lower than atmospheric pressure

Equal to atmospheric pressure

Higher than atmospheric pressure

17. One ton refrigeration corresponds to

80 kcal/ hr

80 kcal/ min

50 kcal/ hr

50 kcal/ min

18. During humidification process, __________ increases.

Relative humidity

Dry bulb temperature

Wet bulb temperature

Specific humidity

19. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

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

Less

More/less depending on size of plant

More

Same

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21. During dehumidification process, the relative humidity

Increases

Decreases

Remains constant

None of these

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

Expansion valve

Evaporator

Condenser

Compressor

23. Pick up the incorrect statement

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

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

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

Remain same

Decreases

Depends on other factors

Increases

25. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

26. The moisture in a refrigerant is removed by

Evaporator

Driers

Dehumidifier

Safety relief valve

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

28. Absorption system normally uses the following refrigerant

Ammonia

Freon-11

CO2

Freon-22

29. 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

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

High pressure side close to receiver

Suction of compressor

Low pressure side near receiver

Delivery of compressor

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

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

Same

Higher

Lower

None of these

33. Which of the following statement is wrong?

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

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.

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

34. The refrigerant widely used in domestic refrigerators is

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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

Capillary tube

Thermostatic valve

Electrically operated throttling valve

Manually operated valve

36. An important characteristic of absorption system of refrigeration is

Quiet operation

Cooling below 0°C

Noisy operation

Very little power consumption

37. 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

Decrease

Remain unaffected

Increase

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

Zero

50

100

20

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

Dehumidification

Humidification

Heating and humidification

Cooling and dehumidification

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

Wet bulb temperature

None of these

Dry bulb temperature

Dew point temperature

Refrigeration & Air-Conditioning Practice Set-1

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