Refrigeration & Air-Conditioning Practice Set-1

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

Less

More/less depending on size of plant

Same

More

2. An important characteristic of absorption system of refrigeration is

Very little power consumption

Noisy operation

Quiet operation

Cooling below 0°C

3. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

4. 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

5. During humidification process, __________ increases.

Specific humidity

Dry bulb temperature

Wet bulb temperature

Relative humidity

6. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ min

80 kcal/ hr

50 kcal/ hr

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

Compressor

Evaporator

Condenser

Expansion valve

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

Before passing through the condenser

After passing through the expansion throttle valve

After passing through the condenser

Before entering the expansion valve

9. During humidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Decreases

Remain same

Increases

Depends on other factors

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11. 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

Absolute humidity

Degree of saturation

Relative humidity

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

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

13. Which of the following statement is wrong?

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

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.

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

14. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

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

CO₂

All of these

R-12

Ammonia

16. The moisture in a refrigerant is removed by

Safety relief valve

Evaporator

Dehumidifier

Driers

17. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

18. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Water and hydrogen

Ammonia, water and hydrogen

None of these

19. During sensible cooling of air ________ decreases.

Relative humidity

Wet bulb temperature

Specific humidity

Dry bulb temperature

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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21. Absorption system normally uses the following refrigerant

Freon-11

CO2

Ammonia

Freon-22

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

Same

None of these

Higher

Lower

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

Remain unaffected

Decrease

Increase

May increase or decrease depending on the type of refrigerant used

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

Dehumidification

Humidification

Heating and humidification

Cooling and dehumidification

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

Zero

0.5

0.75

1.0

26. During dehumidification process, the relative humidity

Increases

None of these

Remains constant

Decreases

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

Very wet vapour

Dry vapour

Wet vapour

High pressure saturated liquid

28. 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.

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.

All of these

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

Low pressure side near receiver

Suction of compressor

Delivery of compressor

High pressure side close to receiver

30. 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

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

56 bars

24 bars

Slightly above atmospheric pressure

Atmospheric pressure

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

Manually operated valve

Electrically operated throttling valve

Capillary tube

Thermostatic valve

33. 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

34. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

35. Under cooling in a refrigeration cycle

Other factors decide C.O.P

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

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

Sulphur sticks which on detection gives white smoke

Using reagents

Halide torch which on detection produces greenish flame lighting

Smelling

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

100

50

Zero

20

38. The vapour pressure of refrigerant should be

Equal to atmospheric pressure

Higher than atmospheric pressure

Could be anything

Lower than atmospheric pressure

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

Orange

Bright green

Yellow

Red

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

Condenser

Evaporator

Compressor

Expansion valve

Refrigeration & Air-Conditioning Practice Set-1

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