Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. 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

Humidity ratio

Relative humidity

Absolute humidity

Degree of saturation

2. One ton refrigeration corresponds to

50 kcal/ hr

80 kcal/ hr

80 kcal/ min

50 kcal/ min

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

Small displacements and low condensing pressures

Small displacements and high condensing pressures

Large displacements and high condensing pressures

Large displacements and low condensing pressures

4. The fluids used in Electrolux refrigerator are

Water and hydrogen

None of these

Ammonia, water and hydrogen

Ammonia and hydrogen

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

Thermostatic valve

Electrically operated throttling valve

Manually operated valve

Capillary tube

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

0.5

1.0

Zero

0.75

7. Which of the following statement is wrong?

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.

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.

8. During humidification process, dry bulb temperature

Decreases

None of these

Increases

Remains constant

9. 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

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

After passing through the expansion throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

Page 2 of 4

11. The reduced ambient air cooling system has

Two cooling turbines and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

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

Condenser

Compressor

Evaporator

Expansion valve

13. The vapour pressure of refrigerant should be

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

Lower than atmospheric pressure

14. For proper refrigeration in a cabinet, if the temperature and vapour pressure difference between cabinet and atmosphere is high, then

Perfectly tight vapour seal should be used

Smaller cabinet should be used

Refrigerant with lower evaporation temperature should be used

Bigger cabinet should be used

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

Dry vapour

Wet vapour

Very wet vapour

High pressure saturated liquid

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

Halide torch which on detection produces greenish flame lighting

Smelling

Sulphur sticks which on detection gives white smoke

Using reagents

17. During sensible heating of air _________ decreases.

Specific humidity

Wet bulb temperature

Dry bulb temperature

Relative humidity

18. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Very little power consumption

Quiet operation

Noisy operation

19. The moisture in a refrigerant is removed by

Evaporator

Dehumidifier

Safety relief valve

Driers

20. The refrigerant widely used in domestic refrigerators is

R-12

Ammonia

Sulphur dioxide

Carbon dioxide

Page 3 of 4

21. During humidification process, __________ increases.

Dry bulb temperature

Relative humidity

Wet bulb temperature

Specific humidity

22. 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

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

Yellow

Orange

Red

Bright green

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

Slightly above atmospheric pressure

24 bars

Atmospheric pressure

56 bars

25. During dehumidification process, the relative humidity

Remains constant

None of these

Increases

Decreases

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

100

Zero

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

Remain same

Decreases

Depends on other factors

Increases

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

More/less depending on size of plant

Same

Less

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

None of these

Higher

Same

Lower

30. Chaperon equation is a relation between

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature, pressure and enthalpy

Page 4 of 4

31. 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

Dew point temperature

None of these

Wet bulb temperature

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

33. Absorption system normally uses the following refrigerant

CO2

Freon-11

Ammonia

Freon-22

34. 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.

35. During sensible cooling of air ________ decreases.

Wet bulb temperature

Dry bulb temperature

Relative humidity

Specific humidity

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

R-12

All of these

CO₂

Ammonia

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

Dehumidification

Cooling and dehumidification

Humidification

Heating and humidification

38. Pick up the incorrect statement

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

Lithium bromide plant can't operate below 0°C

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

Low pressure side near receiver

Suction of compressor

High pressure side close to receiver

Delivery of compressor

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

Evaporator

Expansion valve

Compressor

Condenser

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Refrigeration & Air-Conditioning Practice Set-1

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