Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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Page 1 of 4

1. The vapour pressure of refrigerant should be

Could be anything

Equal to atmospheric pressure

Lower than atmospheric pressure

Higher than atmospheric pressure

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

More/less depending on size of plant

Same

Less

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

Evaporator

Compressor

Condenser

Expansion valve

4. The refrigerant widely used in domestic refrigerators is

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

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

Zero

100

6. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

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

Same

None of these

Higher

Lower

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

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

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

CO₂

All of these

Ammonia

R-12

10. During sensible cooling of air ________ decreases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

Page 2 of 4

11. During humidification process, __________ increases.

Relative humidity

Specific humidity

Wet bulb temperature

Dry bulb temperature

12. During dehumidification process, the relative humidity

None of these

Decreases

Increases

Remains constant

13. 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

14. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Specific humidity

Dry bulb temperature

15. The fluids used in Electrolux refrigerator are

None of these

Water and hydrogen

Ammonia, water and hydrogen

Ammonia and hydrogen

16. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ min

50 kcal/ hr

80 kcal/ hr

17. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Noisy operation

Quiet operation

Very little power consumption

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

Bright green

Red

Yellow

Orange

19. 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

Degree of saturation

Humidity ratio

Relative humidity

Absolute humidity

20. 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

Bigger cabinet should be used

Smaller cabinet should be used

Refrigerant with lower evaporation temperature should be used

Page 3 of 4

21. The moisture in a refrigerant is removed by

Evaporator

Safety relief valve

Driers

Dehumidifier

22. 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

Decrease

Increase

Remain unaffected

23. Which of the following statement is correct?

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

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

All of these

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

24. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

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

Smelling

Sulphur sticks which on detection gives white smoke

Using reagents

Halide torch which on detection produces greenish flame lighting

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

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

After passing through the expansion throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

28. During humidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

29. Under cooling in a refrigeration cycle

Decreases C.O.P

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

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

Increases

Decreases

Remain same

Depends on other factors

Page 4 of 4

31. 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

Wet bulb temperature

None of these

Dry bulb temperature

32. Absorption system normally uses the following refrigerant

Freon-11

Freon-22

CO2

Ammonia

33. 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

A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing

Lithium bromide plant can't operate below 0°C

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

Electrically operated throttling valve

Thermostatic valve

Capillary tube

Manually operated valve

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

Expansion valve

Evaporator

Compressor

Condenser

36. Which of the following statement is wrong?

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.

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

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

0.75

Zero

0.5

1.0

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

Cooling and dehumidification

Heating and humidification

Humidification

Dehumidification

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

High pressure saturated liquid

Dry vapour

Wet vapour

Very wet vapour

40. 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

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Refrigeration & Air-Conditioning Practice Set-1

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