Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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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

Absolute humidity

Humidity ratio

Degree of saturation

Relative humidity

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

Expansion valve

Evaporator

Compressor

Condenser

3. Which of the following statement is correct?

All of these

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.

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

4. The vapour pressure of refrigerant should be

Equal to atmospheric pressure

Could be anything

Lower than atmospheric pressure

Higher than atmospheric pressure

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

Lower

Higher

None of these

Same

6. 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

Refrigerant with lower evaporation temperature should be used

Smaller cabinet should be used

Bigger cabinet should be used

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

Suction of compressor

High pressure side close to receiver

Delivery of compressor

Low pressure side near receiver

8. During sensible heating of air _________ decreases.

Dry bulb temperature

Wet bulb temperature

Relative humidity

Specific humidity

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

Increases

Decreases

Remain same

Depends on other factors

10. Which of the following statement is wrong?

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

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.

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

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

Thermostatic valve

Manually operated valve

Capillary tube

Electrically operated throttling valve

12. 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

13. During dehumidification process, the relative humidity

Remains constant

Decreases

Increases

None of these

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

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Increase

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

Dehumidification

Humidification

Cooling and dehumidification

Heating and humidification

16. 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

17. During humidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

18. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Ammonia, water and hydrogen

Water and hydrogen

None of these

19. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

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

Halide torch which on detection produces greenish flame lighting

Sulphur sticks which on detection gives white smoke

Smelling

Using reagents

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21. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

22. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Quiet operation

Very little power consumption

Noisy operation

23. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

24. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ hr

50 kcal/ hr

80 kcal/ min

25. During sensible cooling of air ________ decreases.

Relative humidity

Specific humidity

Wet bulb temperature

Dry bulb temperature

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

Red

Orange

Bright green

Yellow

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

0.5

0.75

1.0

Zero

28. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Evaporator

Dehumidifier

29. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

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31. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

32. Absorption system normally uses the following refrigerant

Ammonia

Freon-22

CO2

Freon-11

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

Same

More/less depending on size of plant

Less

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

All of these

CO₂

Ammonia

R-12

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

Dry vapour

Very wet vapour

High pressure saturated liquid

Wet vapour

36. During humidification process, __________ increases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

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

100

Zero

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

Expansion valve

Compressor

Condenser

Evaporator

39. 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

40. 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

Dry bulb temperature

Wet bulb temperature

Refrigeration & Air-Conditioning Practice Set-1

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