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

Relative humidity

Absolute humidity

Degree of saturation

Humidity ratio

2. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ min

80 kcal/ hr

50 kcal/ hr

3. During dehumidification process, the relative humidity

None of these

Remains constant

Increases

Decreases

4. 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.

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.

All of these

5. The fluids used in Electrolux refrigerator are

Water and hydrogen

Ammonia and hydrogen

None of these

Ammonia, water and hydrogen

6. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

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

Delivery of compressor

Low pressure side near receiver

Suction of compressor

High pressure side close to receiver

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

After passing through the condenser

After passing through the expansion throttle valve

Before passing through the condenser

Before entering the expansion valve

9. During humidification process, __________ increases.

Wet bulb temperature

Specific humidity

Relative humidity

Dry bulb temperature

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

Decrease

Remain unaffected

Increase

May increase or decrease depending on the type of refrigerant used

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

Higher

Same

None of these

Lower

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

Slightly above atmospheric pressure

Atmospheric pressure

56 bars

24 bars

13. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Could be anything

Equal to atmospheric pressure

Lower than atmospheric pressure

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

Less

More

More/less depending on size of plant

Same

15. During humidification process, dry bulb temperature

None of these

Decreases

Increases

Remains constant

16. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

17. 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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and low condensing pressures

19. 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

20. Absorption system normally uses the following refrigerant

Ammonia

CO2

Freon-11

Freon-22

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21. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Noisy operation

Quiet operation

Very little power consumption

22. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

Evaporator

Condenser

Compressor

Expansion valve

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

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

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

Decreases

Increases

Remain same

Depends on other factors

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

Expansion valve

Evaporator

Condenser

Compressor

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

1.0

0.5

0.75

Zero

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

CO₂

Ammonia

R-12

All of these

29. The refrigerant widely used in domestic refrigerators is

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

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

Capillary tube

Electrically operated throttling valve

Manually operated valve

Thermostatic valve

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31. 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

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

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

Wet vapour

High pressure saturated liquid

Dry vapour

Very wet vapour

34. 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

Bigger cabinet should be used

Refrigerant with lower evaporation temperature should be used

Perfectly tight vapour seal should be used

35. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

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 plant can't operate below 0°C

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

Yellow

Bright green

Red

Orange

37. The moisture in a refrigerant is removed by

Safety relief valve

Evaporator

Driers

Dehumidifier

38. During sensible cooling of air ________ decreases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

Zero

20

50

100

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

Cooling and dehumidification

Dehumidification

Humidification

Heating and humidification

Refrigeration & Air-Conditioning Practice Set-1

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