Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. Which of the following statement is wrong?

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

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.

2. 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

3. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

4. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

None of these

Ammonia and hydrogen

Water and hydrogen

5. 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

Smaller cabinet should be used

Bigger cabinet should be used

Refrigerant with lower evaporation temperature should be used

6. During sensible heating of air _________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

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

Evaporator

Compressor

Condenser

Expansion valve

8. Pick up the incorrect statement

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

Lithium bromide plant can't operate below 0°C

Concentration of solution coming out of lithium bromide generator is more in comparison to that entering the generator

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

10. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

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11. 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.

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

All of these

12. Absorption system normally uses the following refrigerant

Freon-22

Ammonia

Freon-11

CO2

13. An important characteristic of absorption system of refrigeration is

Noisy operation

Cooling below 0°C

Very little power consumption

Quiet operation

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

Same

Lower

Higher

None of these

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

More/less depending on size of plant

Less

Same

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

56 bars

Atmospheric pressure

24 bars

Slightly above atmospheric pressure

17. One ton refrigeration corresponds to

50 kcal/ min

50 kcal/ hr

80 kcal/ hr

80 kcal/ min

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

100

Zero

19. 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

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

Increase

Remain unaffected

Decrease

May increase or decrease depending on the type of refrigerant used

Page 3 of 4

21. During dehumidification process, the relative humidity

Decreases

Remains constant

None of these

Increases

22. During sensible cooling of air ________ decreases.

Relative humidity

Wet bulb temperature

Dry bulb temperature

Specific humidity

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

Condenser

Expansion valve

Compressor

Evaporator

24. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

Increases C.O.P

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

Humidification

Cooling and dehumidification

Heating and humidification

Dehumidification

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

CO₂

All of these

R-12

Ammonia

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

Delivery of compressor

Low pressure side near receiver

Suction of compressor

High pressure side close to receiver

28. During humidification process, __________ increases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

29. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

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

Remain same

Increases

Decreases

Depends on other factors

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31. During humidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

32. The moisture in a refrigerant is removed by

Evaporator

Safety relief valve

Dehumidifier

Driers

33. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

34. 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

35. 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

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

Bright green

Red

Yellow

Orange

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

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion throttle valve

After passing through the condenser

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

Smelling

Using reagents

Halide torch which on detection produces greenish flame lighting

Sulphur sticks which on detection gives white smoke

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

Very wet vapour

Wet vapour

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

Zero

0.5

0.75

1.0

Refrigeration & Air-Conditioning Practice Set-1

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