Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. 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

Perfectly tight vapour seal should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

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

After passing through the expansion throttle valve

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

3. Which of the following statement is correct?

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.

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.

4. During sensible heating of air _________ decreases.

Dry bulb temperature

Wet bulb temperature

Relative humidity

Specific humidity

5. 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

6. The moisture in a refrigerant is removed by

Dehumidifier

Evaporator

Safety relief valve

Driers

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

Dehumidification

Cooling and dehumidification

Heating and humidification

Humidification

8. Which of the following statement is wrong?

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

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.

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

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

Atmospheric pressure

24 bars

Slightly above atmospheric pressure

56 bars

10. During dehumidification process, the relative humidity

Remains constant

Increases

None of these

Decreases

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11. During sensible cooling of air ________ decreases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

High pressure saturated liquid

Very wet vapour

Dry vapour

Wet vapour

13. One ton refrigeration corresponds to

80 kcal/ min

80 kcal/ hr

50 kcal/ min

50 kcal/ hr

14. During humidification process, dry bulb temperature

Increases

None of these

Remains constant

Decreases

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

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and low condensing pressures

Small displacements and high condensing pressures

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

Ammonia

CO₂

R-12

All of these

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

0.75

1.0

0.5

Zero

18. Chaperon equation is a relation between

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

19. 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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

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

Electrically operated throttling valve

Thermostatic valve

Manually operated valve

Capillary tube

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

Lower

Higher

Same

None of these

22. 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

23. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Noisy operation

Very little power consumption

Quiet operation

24. During humidification process, __________ increases.

Relative humidity

Wet bulb temperature

Dry bulb temperature

Specific humidity

25. The vapour pressure of refrigerant should be

Could be anything

Equal to atmospheric pressure

Higher than atmospheric pressure

Lower than atmospheric pressure

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

Wet vapour

Dry saturated vapour

Saturated liquid

Superheated vapour

27. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

28. Absorption system normally uses the following refrigerant

Ammonia

CO2

Freon-22

Freon-11

29. The refrigerant widely used in domestic refrigerators is

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

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

Increase

Decrease

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Evaporator

Compressor

Expansion valve

Condenser

32. 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

33. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

Water and hydrogen

Ammonia and hydrogen

None of these

34. 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

Relative humidity

Humidity ratio

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

Condenser

Evaporator

Compressor

Expansion valve

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

More/less depending on size of plant

Less

Same

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

Using reagents

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Smelling

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

Depends on other factors

Remain same

Decreases

Increases

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

Zero

100

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

Yellow

Orange

Bright green

Red

Refrigeration & Air-Conditioning Practice Set-1

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