Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Water and hydrogen

Ammonia, water and hydrogen

None of these

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

Before entering the expansion valve

After passing through the expansion throttle valve

Before passing through the condenser

After passing through the condenser

3. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature and enthalpy

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

Atmospheric pressure

56 bars

24 bars

Slightly above atmospheric pressure

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

Increases

Decreases

Remain same

Depends on other factors

6. 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

Perfectly tight vapour seal should be used

Smaller cabinet should be used

Bigger cabinet should be used

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

CO₂

All of these

Ammonia

R-12

8. 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

Wet bulb temperature

None of these

Dew point temperature

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

Using reagents

Halide torch which on detection produces greenish flame lighting

Smelling

Sulphur sticks which on detection gives white smoke

10. An important characteristic of absorption system of refrigeration is

Noisy operation

Cooling below 0°C

Very little power consumption

Quiet operation

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

Evaporator

Condenser

Compressor

Expansion valve

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

Orange

Yellow

Red

Bright green

13. 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

14. The moisture in a refrigerant is removed by

Safety relief valve

Driers

Evaporator

Dehumidifier

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

Humidification

Heating and humidification

Dehumidification

Cooling and dehumidification

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

Zero

100

17. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

Zero

1.0

0.5

0.75

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

Condenser

Compressor

Evaporator

Expansion valve

20. The refrigerant widely used in domestic refrigerators is

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

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21. During humidification process, dry bulb temperature

Increases

None of these

Remains constant

Decreases

22. Absorption system normally uses the following refrigerant

CO2

Freon-11

Freon-22

Ammonia

23. Which of the following statement is wrong?

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.

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.

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

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

Manually operated valve

Capillary tube

Thermostatic valve

Electrically operated throttling valve

26. During dehumidification process, the relative humidity

Remains constant

None of these

Decreases

Increases

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

Lower

None of these

Same

Higher

28. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

One cooling turbine and two heat exchangers

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

Decrease

May increase or decrease depending on the type of refrigerant used

Remain unaffected

Increase

30. One ton refrigeration corresponds to

80 kcal/ min

80 kcal/ hr

50 kcal/ min

50 kcal/ hr

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

Wet vapour

Very wet vapour

Dry vapour

High pressure saturated liquid

32. During sensible heating of air _________ decreases.

Dry bulb temperature

Specific humidity

Relative humidity

Wet bulb temperature

33. Under cooling in a refrigeration cycle

Other factors decide C.O.P

C.O.P remains unaltered

Increases C.O.P

Decreases C.O.P

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

More/less depending on size of plant

Less

Same

35. 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.

36. 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

37. The vapour pressure of refrigerant should be

Equal to atmospheric pressure

Lower than atmospheric pressure

Higher than atmospheric pressure

Could be anything

38. During sensible cooling of air ________ decreases.

Specific humidity

Dry bulb temperature

Wet bulb temperature

Relative humidity

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

Delivery of compressor

Low pressure side near receiver

High pressure side close to receiver

Suction of compressor

40. 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

Humidity ratio

Relative humidity

Absolute humidity

Refrigeration & Air-Conditioning Practice Set-1

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