Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. 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

2. During dehumidification process, the relative humidity

None of these

Increases

Remains constant

Decreases

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

More/less depending on size of plant

Same

Less

4. 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

5. The fluids used in Electrolux refrigerator are

None of these

Ammonia and hydrogen

Water and hydrogen

Ammonia, water and hydrogen

6. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Higher than atmospheric pressure

Equal to atmospheric pressure

Could be anything

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

0.5

0.75

Zero

1.0

8. During sensible heating of air _________ decreases.

Wet bulb temperature

Dry bulb temperature

Specific humidity

Relative humidity

9. 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

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

Increases

Remain same

Decreases

Depends on other factors

Page 2 of 4

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

Zero

100

12. Which of the following statement is wrong?

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

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.

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

13. The refrigerant widely used in domestic refrigerators is

Ammonia

Sulphur dioxide

Carbon dioxide

R-12

14. Which of the following statement is correct?

Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser.

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

In vapour absorption refrigerator, the compression of refrigerant is avoided.

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

Atmospheric pressure

Slightly above atmospheric pressure

24 bars

56 bars

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion throttle valve

Before passing through the condenser

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

18. 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

Bigger cabinet should be used

Smaller cabinet should be used

Perfectly tight vapour seal should be used

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

High pressure side close to receiver

Low pressure side near receiver

Suction of compressor

Delivery of compressor

20. Pick up the incorrect statement

Lithium bromide plant can't operate below 0°C

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

A separator is used in lithium bromide plant to remove the unwanted water vapour by condensing

Page 3 of 4

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

Increase

Remain unaffected

May increase or decrease depending on the type of refrigerant used

Decrease

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

Wet vapour

Dry vapour

Very wet vapour

High pressure saturated liquid

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

Red

Orange

Bright green

Yellow

24. During sensible cooling of air ________ decreases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

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

Evaporator

Condenser

Expansion valve

Compressor

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

Ammonia

All of these

CO₂

R-12

27. During humidification process, __________ increases.

Dry bulb temperature

Relative humidity

Specific humidity

Wet bulb temperature

28. The moisture in a refrigerant is removed by

Evaporator

Dehumidifier

Safety relief valve

Driers

29. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Quiet operation

Noisy operation

Very little power consumption

30. One ton refrigeration corresponds to

80 kcal/ min

80 kcal/ hr

50 kcal/ hr

50 kcal/ min

Page 4 of 4

31. Absorption system normally uses the following refrigerant

Freon-22

CO2

Freon-11

Ammonia

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

Compressor

Evaporator

Expansion valve

Condenser

33. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

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

Heating and humidification

Humidification

Dehumidification

Cooling and dehumidification

35. 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

36. 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

Relative humidity

Degree of saturation

Humidity ratio

Absolute humidity

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

Smelling

Halide torch which on detection produces greenish flame lighting

Using reagents

Sulphur sticks which on detection gives white smoke

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

Dry bulb temperature

None of these

Wet bulb temperature

39. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

40. During humidification process, dry bulb temperature

Decreases

Increases

Remains constant

None of these

Refrigeration & Air-Conditioning Practice Set-1

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