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.

All of these

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

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

2. Absorption system normally uses the following refrigerant

Ammonia

CO2

Freon-11

Freon-22

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

Condenser

Evaporator

Expansion valve

Compressor

4. 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

Dry bulb temperature

None of these

5. During sensible cooling of air ________ decreases.

Relative humidity

Dry bulb temperature

Wet bulb temperature

Specific humidity

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

Electrically operated throttling valve

Capillary tube

Thermostatic valve

Manually operated valve

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

Heating and humidification

Cooling and dehumidification

Dehumidification

Humidification

8. 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

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

Delivery of compressor

Suction of compressor

High pressure side close to receiver

Low pressure side near receiver

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

Depends on other factors

Decreases

Increases

Remain same

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11. An important characteristic of absorption system of refrigeration is

Quiet operation

Cooling below 0°C

Very little power consumption

Noisy operation

12. 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

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

Orange

Bright green

Red

Yellow

14. During dehumidification process, the relative humidity

Decreases

None of these

Remains constant

Increases

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

R-12

Ammonia

All of these

CO₂

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

Dry vapour

Wet vapour

Very wet vapour

High pressure saturated liquid

17. 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

Absolute humidity

Humidity ratio

Degree of saturation

Relative humidity

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

Compressor

Expansion valve

Evaporator

Condenser

19. Which of the following statement is wrong?

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

The performance of the vapour compression refrigerator varies considerably with both vaporising and condensing temperatures.

The effect of under-cooling the liquid refrigerant is to decrease the coefficient of performance.

In ammonia-hydrogen (Electrolux) refrigerator, no compressor, pump or fan is required.

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

Large displacements and low condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

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21. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

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

Zero

100

23. 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

24. The moisture in a refrigerant is removed by

Driers

Dehumidifier

Evaporator

Safety relief valve

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

Higher

Lower

Same

None of these

26. During humidification process, dry bulb temperature

Increases

Remains constant

None of these

Decreases

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

Smelling

Halide torch which on detection produces greenish flame lighting

Using reagents

Sulphur sticks which on detection gives white smoke

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

24 bars

56 bars

Atmospheric pressure

Slightly above atmospheric pressure

29. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Increases C.O.P

Other factors decide C.O.P

Decreases C.O.P

30. During sensible heating of air _________ decreases.

Wet bulb temperature

Dry bulb temperature

Relative humidity

Specific humidity

Page 4 of 4

31. During humidification process, __________ increases.

Wet bulb temperature

Specific humidity

Relative humidity

Dry bulb temperature

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

Less

More/less depending on size of plant

Same

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

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Increase

Decrease

34. One ton refrigeration corresponds to

50 kcal/ min

50 kcal/ hr

80 kcal/ hr

80 kcal/ min

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion throttle valve

36. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

38. The fluids used in Electrolux refrigerator are

Water and hydrogen

Ammonia and hydrogen

Ammonia, water and hydrogen

None of these

39. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

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

0.5

0.75

1.0

Zero

Refrigeration & Air-Conditioning Practice Set-1

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