Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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Page 1 of 4

1. The fluids used in Electrolux refrigerator are

None of these

Ammonia and hydrogen

Ammonia, water and hydrogen

Water and hydrogen

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

Lower

None of these

Same

Higher

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

1.0

0.75

0.5

Zero

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

Delivery of compressor

High pressure side close to receiver

Suction of compressor

Low pressure side near receiver

5. During humidification process, dry bulb temperature

Decreases

None of these

Increases

Remains constant

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

Electrically operated throttling valve

Thermostatic valve

Manually operated valve

Capillary tube

7. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

Dry bulb temperature

Dew point temperature

Wet bulb temperature

None of these

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

Dehumidification

Heating and humidification

Humidification

Cooling and dehumidification

9. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ min

50 kcal/ hr

80 kcal/ min

10. Which of the following statement is wrong?

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.

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. The centrifugal compressors are generally used for refrigerants that require

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

12. 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

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

Compressor

Condenser

Expansion valve

Evaporator

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

Using reagents

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Smelling

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

Condenser

Compressor

Evaporator

Expansion valve

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

CO₂

R-12

All of these

Ammonia

17. The moisture in a refrigerant is removed by

Dehumidifier

Safety relief valve

Evaporator

Driers

18. During dehumidification process, the relative humidity

None of these

Increases

Decreases

Remains constant

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

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

20. Under cooling in a refrigeration cycle

Increases C.O.P

Decreases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Page 3 of 4

21. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

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

22. Absorption system normally uses the following refrigerant

Freon-11

Ammonia

CO2

Freon-22

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

Atmospheric pressure

24 bars

Slightly above atmospheric pressure

56 bars

24. The vapour pressure of refrigerant should be

Higher than atmospheric pressure

Equal to atmospheric pressure

Could be anything

Lower than atmospheric pressure

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

Red

Orange

Yellow

Bright green

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

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

Smaller cabinet should be used

Perfectly tight vapour seal should be used

27. During sensible heating of air _________ decreases.

Wet bulb temperature

Dry bulb temperature

Relative humidity

Specific humidity

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

Very wet vapour

Dry vapour

High pressure saturated liquid

Wet vapour

29. An important characteristic of absorption system of refrigeration is

Very little power consumption

Noisy operation

Cooling below 0°C

Quiet operation

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

More/less depending on size of plant

Same

Less

Page 4 of 4

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

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

Decrease

32. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

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. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

35. Which of the following statement is correct?

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

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

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

100

Zero

37. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

38. During sensible cooling of air ________ decreases.

Dry bulb temperature

Relative humidity

Wet bulb temperature

Specific humidity

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

Remain same

Decreases

Depends on other factors

Increases

40. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

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Refrigeration & Air-Conditioning Practice Set-1

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