Refrigeration & Air-Conditioning Practice Set-1

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

Dehumidification

Heating and humidification

Cooling and dehumidification

Humidification

2. 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

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

Dry vapour

High pressure saturated liquid

Wet vapour

Very wet vapour

4. 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

Dew point temperature

None of these

Dry bulb temperature

5. During humidification process, dry bulb temperature

None of these

Increases

Decreases

Remains constant

6. 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

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

Compressor

Expansion valve

Condenser

Evaporator

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

Low pressure side near receiver

Delivery of compressor

Suction of compressor

High pressure side close to receiver

9. Which of the following statement is correct?

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

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

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

After passing through the expansion throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

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

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

Decrease

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

100

50

Zero

20

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

Slightly above atmospheric pressure

24 bars

56 bars

Atmospheric pressure

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

CO₂

Ammonia

All of these

R-12

15. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ hr

80 kcal/ min

50 kcal/ min

16. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then

Perfectly tight vapour seal should be used

Bigger cabinet should be used

Refrigerant with lower evaporation temperature should be used

Smaller cabinet should be used

17. During dehumidification process, the relative humidity

Increases

None of these

Remains constant

Decreases

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

Yellow

Bright green

Orange

Red

19. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Relative humidity

Wet bulb temperature

20. Which of the following statement is wrong?

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

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.

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21. The moisture in a refrigerant is removed by

Driers

Dehumidifier

Evaporator

Safety relief valve

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

Less

Same

More

More/less depending on size of plant

23. The reduced ambient air cooling system has

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

Two cooling turbines and one heat exchanger

One cooling turbine and two heat exchangers

24. Chaperon equation is a relation between

Temperature and enthalpy

Specific volume and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

25. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

None of these

Water and hydrogen

Ammonia, water and hydrogen

26. 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

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

Lithium bromide used in vapour absorption cycle is non volatile

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

0.5

0.75

Zero

1.0

28. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Equal to atmospheric pressure

Higher than atmospheric pressure

Could be anything

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

Depends on other factors

Remain same

Increases

Decreases

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

Thermostatic valve

Electrically operated throttling valve

Manually operated valve

Capillary tube

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31. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Very little power consumption

Quiet operation

Noisy operation

32. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Specific humidity

Dry bulb temperature

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

Same

Lower

None of these

Higher

34. 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

Absolute humidity

Relative humidity

35. Absorption system normally uses the following refrigerant

Ammonia

Freon-22

CO2

Freon-11

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

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

37. During humidification process, __________ increases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

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

Evaporator

Compressor

Expansion valve

Condenser

39. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

40. Under cooling in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Decreases C.O.P

Increases C.O.P

Refrigeration & Air-Conditioning Practice Set-1

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