Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. 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.

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

All of these

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

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

Halide torch which on detection produces greenish flame lighting

Smelling

Using reagents

Sulphur sticks which on detection gives white smoke

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

Orange

Red

Bright green

Yellow

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

Increases

Depends on other factors

Remain same

Decreases

5. One ton refrigeration corresponds to

80 kcal/ min

50 kcal/ min

80 kcal/ hr

50 kcal/ hr

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

7. 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.

8. The vapour pressure of refrigerant should be

Could be anything

Lower than atmospheric pressure

Equal to atmospheric pressure

Higher than atmospheric pressure

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

Dry vapour

Very wet vapour

Wet vapour

High pressure saturated liquid

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

Wet bulb temperature

Dry bulb temperature

None of these

Dew point temperature

Page 2 of 4

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

12. 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

13. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

14. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

None of these

Ammonia, water and hydrogen

Water and hydrogen

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

Heating and humidification

Dehumidification

Cooling and dehumidification

Humidification

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

Expansion valve

Evaporator

Condenser

Compressor

17. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

18. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

19. An important characteristic of absorption system of refrigeration is

Very little power consumption

Quiet operation

Noisy operation

Cooling below 0°C

20. During dehumidification process, the relative humidity

Increases

None of these

Remains constant

Decreases

Page 3 of 4

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

1.0

Zero

0.75

0.5

22. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

23. 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

Degree of saturation

Humidity ratio

Absolute humidity

24. Absorption system normally uses the following refrigerant

CO2

Ammonia

Freon-11

Freon-22

25. During humidification process, dry bulb temperature

Decreases

Increases

Remains constant

None of these

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

24 bars

Slightly above atmospheric pressure

56 bars

Atmospheric pressure

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

Zero

100

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

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

After passing through the expansion throttle valve

29. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

Other factors decide C.O.P

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

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

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31. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

32. 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

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

High pressure side close to receiver

Delivery of compressor

Low pressure side near receiver

Suction of compressor

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

More/less depending on size of plant

Same

Less

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

None of these

Lower

Higher

Same

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

Expansion valve

Compressor

Condenser

Evaporator

37. The moisture in a refrigerant is removed by

Safety relief valve

Driers

Evaporator

Dehumidifier

38. During humidification process, __________ increases.

Relative humidity

Wet bulb temperature

Dry bulb temperature

Specific humidity

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

Ammonia

All of these

CO₂

R-12

40. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

Refrigeration & Air-Conditioning Practice Set-1

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