Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. An important characteristic of absorption system of refrigeration is

Very little power consumption

Noisy operation

Cooling below 0°C

Quiet operation

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

Halide torch which on detection produces greenish flame lighting

Using reagents

Sulphur sticks which on detection gives white smoke

Smelling

3. During humidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

4. The reduced ambient air cooling system has

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and two heat exchangers

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

Evaporator

Expansion valve

Condenser

Compressor

6. One ton refrigeration corresponds to

50 kcal/ min

50 kcal/ hr

80 kcal/ hr

80 kcal/ min

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

Capillary tube

Manually operated valve

Electrically operated throttling valve

Thermostatic valve

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

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

0.75

0.5

1.0

Zero

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

Slightly above atmospheric pressure

Atmospheric pressure

56 bars

24 bars

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

Wet vapour

High pressure saturated liquid

Dry vapour

Very wet vapour

13. Which of the following statement is wrong?

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.

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.

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

15. 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

16. The fluids used in Electrolux refrigerator are

None of these

Ammonia and hydrogen

Water and hydrogen

Ammonia, water and hydrogen

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

All of these

R-12

Ammonia

CO₂

18. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

19. Which of the following statement is correct?

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

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.

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

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

Higher

Lower

None of these

Same

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21. 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

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

Perfectly tight vapour seal should be used

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

Before passing through the condenser

After passing through the expansion throttle valve

After passing through the condenser

Before entering the expansion valve

23. During sensible cooling of air ________ decreases.

Specific humidity

Wet bulb temperature

Relative humidity

Dry bulb temperature

24. During sensible heating of air _________ decreases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

25. 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

Absolute humidity

Degree of saturation

Humidity ratio

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

Yellow

Red

Bright green

Orange

27. During dehumidification process, the relative humidity

Decreases

Remains constant

Increases

None of these

28. The moisture in a refrigerant is removed by

Driers

Safety relief valve

Evaporator

Dehumidifier

29. 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

30. During humidification process, __________ increases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

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

Decreases

Depends on other factors

Remain same

Increases

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

Small displacements and low condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

Small displacements and high condensing pressures

33. 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

Dry bulb temperature

Wet bulb temperature

None of these

34. The refrigerant widely used in domestic refrigerators is

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

100

Zero

36. The vapour pressure of refrigerant should be

Could be anything

Equal to atmospheric pressure

Lower than atmospheric pressure

Higher than atmospheric pressure

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

More/less depending on size of plant

Less

Same

38. Absorption system normally uses the following refrigerant

CO2

Freon-22

Ammonia

Freon-11

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

Condenser

Evaporator

Compressor

Expansion valve

40. 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

Refrigeration & Air-Conditioning Practice Set-1

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