Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

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

Depends on other factors

Decreases

Remain same

Increases

3. An important characteristic of absorption system of refrigeration is

Very little power consumption

Cooling below 0°C

Quiet operation

Noisy operation

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

Dehumidification

Heating and humidification

Cooling and dehumidification

Humidification

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

Same

Less

More/less depending on size of plant

6. 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

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

Expansion valve

Evaporator

Condenser

Compressor

8. 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

Perfectly tight vapour seal should be used

Refrigerant with lower evaporation temperature should be used

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

1.0

0.5

Zero

0.75

10. Absorption system normally uses the following refrigerant

CO2

Freon-11

Freon-22

Ammonia

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

CO₂

R-12

Ammonia

All of these

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

Slightly above atmospheric pressure

Atmospheric pressure

24 bars

56 bars

13. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Lower than atmospheric pressure

Equal to atmospheric pressure

Could be anything

14. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

15. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

16. During dehumidification process, the relative humidity

Decreases

None of these

Remains constant

Increases

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

Wet vapour

Very wet vapour

High pressure saturated liquid

Dry vapour

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

100

Zero

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

Delivery of compressor

Low pressure side near receiver

High pressure side close to receiver

Suction of compressor

20. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ min

80 kcal/ min

50 kcal/ hr

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

Bright green

Red

Yellow

Orange

22. Under cooling in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

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

Condenser

Compressor

Expansion valve

Evaporator

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

25. During sensible cooling of air ________ decreases.

Wet bulb temperature

Relative humidity

Dry bulb temperature

Specific humidity

26. 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

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

None of these

Higher

Same

Lower

28. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

One cooling turbine and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

29. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

30. The moisture in a refrigerant is removed by

Safety relief valve

Evaporator

Driers

Dehumidifier

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

32. During humidification process, __________ increases.

Specific humidity

Wet bulb temperature

Relative humidity

Dry bulb temperature

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

Before entering the expansion valve

After passing through the expansion throttle valve

Before passing through the condenser

After passing through the condenser

34. During humidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

35. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

36. 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

Dry bulb temperature

Dew point temperature

37. 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

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

In vapour compression cycle, the useful part of the heat transfer is at the condenser.

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

Halide torch which on detection produces greenish flame lighting

Using reagents

Sulphur sticks which on detection gives white smoke

Smelling

40. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

Water and hydrogen

None of these

Ammonia and hydrogen

Refrigeration & Air-Conditioning Practice Set-1

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