Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

2. During sensible cooling of air ________ decreases.

Wet bulb temperature

Specific humidity

Dry bulb temperature

Relative humidity

3. The moisture in a refrigerant is removed by

Dehumidifier

Driers

Evaporator

Safety relief valve

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

Heating and humidification

Dehumidification

Humidification

Cooling and dehumidification

5. During humidification process, __________ increases.

Wet bulb temperature

Dry bulb temperature

Specific humidity

Relative humidity

6. During humidification process, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

Wet vapour

Very wet vapour

High pressure saturated liquid

Dry vapour

8. Under cooling in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

Decreases C.O.P

9. Which of the following statement is wrong?

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.

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.

10. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ hr

80 kcal/ min

50 kcal/ hr

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11. Absorption system normally uses the following refrigerant

Freon-11

Ammonia

Freon-22

CO2

12. 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

13. During dehumidification process, the relative humidity

Increases

None of these

Decreases

Remains constant

14. 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

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

Delivery of compressor

High pressure side close to receiver

Low pressure side near receiver

Suction of compressor

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

Decrease

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

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

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Using reagents

Smelling

18. The refrigerant widely used in domestic refrigerators is

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion throttle valve

20. Pick up the incorrect statement

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

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

Page 3 of 4

21. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Dry bulb temperature

Specific humidity

22. An important characteristic of absorption system of refrigeration is

Noisy operation

Quiet operation

Cooling below 0°C

Very little power consumption

23. 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

Absolute humidity

Relative humidity

Degree of saturation

Humidity ratio

24. The vapour pressure of refrigerant should be

Equal to atmospheric pressure

Lower than atmospheric pressure

Higher than atmospheric pressure

Could be anything

25. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

Ammonia and hydrogen

None of these

Water and hydrogen

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

Evaporator

Condenser

Expansion valve

Compressor

27. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

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

Zero

1.0

0.5

0.75

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

CO₂

All of these

R-12

Ammonia

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

Wet vapour

Dry saturated vapour

Saturated liquid

Superheated vapour

Page 4 of 4

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

100

Zero

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

Bright green

Red

Yellow

Orange

33. 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

Refrigerant with lower evaporation temperature should be used

Perfectly tight vapour seal should be used

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

Same

More/less depending on size of plant

Less

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

Compressor

Evaporator

Expansion valve

Condenser

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

Capillary tube

Thermostatic valve

Manually operated valve

Electrically operated throttling valve

37. Which of the following statement is correct?

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.

In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke.

All of these

38. 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

Wet bulb temperature

None of these

Dry bulb temperature

39. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

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

Decreases

Depends on other factors

Remain same

Increases

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Refrigeration & Air-Conditioning Practice Set-1

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