Refrigeration & Air-Conditioning Practice Set-1

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1. 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

Relative humidity

Absolute humidity

Degree of saturation

2. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

Ammonia and hydrogen

Water and hydrogen

None of these

3. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Equal to atmospheric pressure

Could be anything

Lower than atmospheric pressure

4. During sensible heating of air _________ decreases.

Relative humidity

Specific humidity

Wet bulb temperature

Dry bulb temperature

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

6. An important characteristic of absorption system of refrigeration is

Very little power consumption

Cooling below 0°C

Quiet operation

Noisy operation

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

Humidification

Heating and humidification

Cooling and dehumidification

Dehumidification

8. 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

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

Lower

None of these

Higher

Same

10. 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

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

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

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

Zero

1.0

0.5

0.75

13. During humidification process, __________ increases.

Specific humidity

Wet bulb temperature

Dry bulb temperature

Relative humidity

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

Yellow

Bright green

Red

Orange

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

Compressor

Condenser

Expansion valve

Evaporator

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

Expansion valve

Compressor

Evaporator

Condenser

17. Chaperon equation is a relation between

Temperature and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

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

Ammonia

CO₂

R-12

All of these

19. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Dehumidifier

Evaporator

20. 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.

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.

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

Less

Same

More

More/less depending on size of plant

22. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

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

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

23. 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

Smaller cabinet should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

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

Zero

50

100

20

25. During humidification process, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion throttle valve

Before passing through the condenser

27. Absorption system normally uses the following refrigerant

Freon-11

CO2

Ammonia

Freon-22

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

Increases

Depends on other factors

Decreases

Remain same

29. Which of the following statement is correct?

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

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

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

30. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

Manually operated valve

Thermostatic valve

Electrically operated throttling valve

Capillary tube

32. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Relative humidity

Wet bulb temperature

33. During dehumidification process, the relative humidity

Increases

None of these

Decreases

Remains constant

34. 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

35. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ hr

80 kcal/ hr

50 kcal/ min

36. 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

None of these

Wet bulb temperature

Dry bulb temperature

37. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

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

Dry vapour

High pressure saturated liquid

Very wet vapour

Wet vapour

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

Atmospheric pressure

56 bars

Slightly above atmospheric pressure

24 bars

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

High pressure side close to receiver

Low pressure side near receiver

Delivery of compressor

Suction of compressor

Refrigeration & Air-Conditioning Practice Set-1

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