Refrigeration & Air-Conditioning Practice Set-1

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1. 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

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

Compressor

Evaporator

Expansion valve

Condenser

3. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

None of these

Dew point temperature

Dry bulb temperature

Wet bulb temperature

4. During humidification process, dry bulb temperature

None of these

Remains constant

Decreases

Increases

5. The moisture in a refrigerant is removed by

Dehumidifier

Safety relief valve

Driers

Evaporator

6. During dehumidification process, the relative humidity

Increases

Remains constant

None of these

Decreases

7. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

Lithium bromide plant can't operate below 0°C

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

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

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

Same

Less

More/less depending on size of plant

More

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

Humidification

Heating and humidification

Dehumidification

Cooling and dehumidification

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11. Under cooling in a refrigeration cycle

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

Increases C.O.P

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

Very wet vapour

High pressure saturated liquid

Dry vapour

Wet vapour

13. 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

Smaller cabinet should be used

Bigger cabinet should be used

Perfectly tight vapour seal should be used

14. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

15. Absorption system normally uses the following refrigerant

CO2

Freon-11

Freon-22

Ammonia

16. Which of the following statement is correct?

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.

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.

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

Increases

Remain same

Depends on other factors

Decreases

18. 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

19. 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

20. The fluids used in Electrolux refrigerator are

Water and hydrogen

Ammonia, water and hydrogen

Ammonia and hydrogen

None of these

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

Capillary tube

Manually operated valve

Thermostatic valve

Electrically operated throttling valve

22. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

23. 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

24. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Lower than atmospheric pressure

Equal to atmospheric pressure

25. 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 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.

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

None of these

Lower

Higher

Same

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

All of these

Ammonia

CO₂

R-12

28. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

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

0.75

1.0

Zero

0.5

30. 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

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

Evaporator

Condenser

Compressor

Expansion valve

32. During sensible cooling of air ________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

33. One ton refrigeration corresponds to

50 kcal/ hr

50 kcal/ min

80 kcal/ hr

80 kcal/ min

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

Bright green

Red

Orange

Yellow

35. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

Specific volume and enthalpy

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

Halide torch which on detection produces greenish flame lighting

Smelling

Using reagents

Sulphur sticks which on detection gives white smoke

37. An important characteristic of absorption system of refrigeration is

Quiet operation

Noisy operation

Cooling below 0°C

Very little power consumption

38. 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

Humidity ratio

Relative humidity

39. During sensible heating of air _________ decreases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

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

100

20

Zero

50

Refrigeration & Air-Conditioning Practice Set-1

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