Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Water and hydrogen

None of these

Ammonia, water and hydrogen

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

Orange

Yellow

Bright green

Red

3. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

4. 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

5. 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

Perfectly tight vapour seal should be used

Bigger cabinet should be used

Refrigerant with lower evaporation temperature should be used

6. 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

7. An important characteristic of absorption system of refrigeration is

Very little power consumption

Noisy operation

Quiet operation

Cooling below 0°C

8. The moisture in a refrigerant is removed by

Safety relief valve

Dehumidifier

Evaporator

Driers

9. One ton refrigeration corresponds to

80 kcal/ hr

80 kcal/ min

50 kcal/ hr

50 kcal/ min

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

Atmospheric pressure

56 bars

24 bars

Slightly above atmospheric pressure

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11. The refrigerant widely used in domestic refrigerators is

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

13. Absorption system normally uses the following refrigerant

Freon-11

Ammonia

Freon-22

CO2

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

Expansion valve

Condenser

Evaporator

Compressor

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

CO₂

R-12

Ammonia

All of these

16. During humidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

17. During dehumidification process, the relative humidity

Increases

Decreases

Remains constant

None of these

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

Manually operated valve

Electrically operated throttling valve

Capillary tube

Thermostatic valve

19. During humidification process, __________ increases.

Specific humidity

Wet bulb temperature

Relative humidity

Dry bulb temperature

20. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and two heat exchangers

Page 3 of 4

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

Same

Less

More/less depending on size of plant

22. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Increases C.O.P

Decreases C.O.P

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

High pressure side close to receiver

Suction of compressor

Low pressure side near receiver

Delivery of compressor

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

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

1.0

0.5

0.75

Zero

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

Same

Higher

Lower

None of these

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

Dehumidification

Cooling and dehumidification

Humidification

Heating and humidification

28. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

29. During sensible heating of air _________ decreases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

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

100

Zero

Page 4 of 4

31. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

32. Which of the following statement is correct?

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.

All of these

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

33. 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

Wet bulb temperature

None of these

Dew point temperature

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

Compressor

Evaporator

Expansion valve

Condenser

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

High pressure saturated liquid

Wet vapour

Dry vapour

Very wet vapour

36. 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

Absolute humidity

Relative humidity

Humidity ratio

37. 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

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

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

Depends on other factors

Decreases

Remain same

Increases

40. 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 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.

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Refrigeration & Air-Conditioning Practice Set-1

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