Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. 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

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

Yellow

Red

Bright green

Orange

3. 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

4. The moisture in a refrigerant is removed by

Safety relief valve

Dehumidifier

Driers

Evaporator

5. The refrigerant widely used in domestic refrigerators is

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

6. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

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

Ammonia

All of these

R-12

CO₂

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

Evaporator

Expansion valve

Condenser

Compressor

9. During dehumidification process, the relative humidity

None of these

Increases

Decreases

Remains constant

10. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Wet bulb temperature

Relative humidity

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11. Pick up the incorrect statement

Lithium bromide used in vapour absorption cycle is non volatile

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

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

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

May increase or decrease depending on the type of refrigerant used

Increase

Remain unaffected

Decrease

13. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

None of these

Water and hydrogen

Ammonia and hydrogen

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

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

15. An important characteristic of absorption system of refrigeration is

Quiet operation

Noisy operation

Cooling below 0°C

Very little power consumption

16. 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

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

Thermostatic valve

Electrically operated throttling valve

Capillary tube

Manually operated valve

18. The vapour pressure of refrigerant should be

Equal to atmospheric pressure

Lower than atmospheric pressure

Could be anything

Higher than atmospheric pressure

19. During humidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Decreases

Increases

Depends on other factors

Remain same

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21. During humidification process, __________ increases.

Dry bulb temperature

Specific humidity

Wet bulb temperature

Relative humidity

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

0.75

Zero

0.5

1.0

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

Suction of compressor

Delivery of compressor

Low pressure side near receiver

High pressure side close to receiver

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

More/less depending on size of plant

Less

Same

25. Which of the following statement is wrong?

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

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.

26. Absorption system normally uses the following refrigerant

Ammonia

Freon-22

CO2

Freon-11

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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

Humidification

Heating and humidification

Dehumidification

Cooling and dehumidification

29. 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

Dew point temperature

None of these

Dry bulb temperature

30. Under cooling in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

Other factors decide C.O.P

C.O.P remains unaltered

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31. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

32. During sensible heating of air _________ decreases.

Relative humidity

Dry bulb temperature

Wet bulb temperature

Specific humidity

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

Evaporator

Condenser

Compressor

Expansion valve

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

Sulphur sticks which on detection gives white smoke

Using reagents

Halide torch which on detection produces greenish flame lighting

Smelling

35. 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 condenser

After passing through the expansion throttle valve

36. 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

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

Zero

100

38. 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

39. One ton refrigeration corresponds to

80 kcal/ hr

80 kcal/ min

50 kcal/ min

50 kcal/ hr

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

None of these

Higher

Same

Lower

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