Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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

Expansion valve

Condenser

Evaporator

Compressor

2. Pick up the incorrect statement

Lithium bromide plant can't operate below 0°C

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

Lithium bromide used in vapour absorption cycle is non volatile

3. One ton refrigeration corresponds to

50 kcal/ hr

50 kcal/ min

80 kcal/ hr

80 kcal/ min

4. 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.

5. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

6. Absorption system normally uses the following refrigerant

Freon-11

Ammonia

CO2

Freon-22

7. Which of the following statement is correct?

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.

All of these

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

8. 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

9. 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

Dew point temperature

Wet bulb temperature

Dry bulb temperature

10. The moisture in a refrigerant is removed by

Safety relief valve

Driers

Evaporator

Dehumidifier

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

One cooling turbine and one heat exchanger

Two cooling turbines and two heat exchangers

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

24 bars

56 bars

Slightly above atmospheric pressure

Atmospheric pressure

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

Smelling

Sulphur sticks which on detection gives white smoke

Halide torch which on detection produces greenish flame lighting

Using reagents

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

High pressure saturated liquid

Wet vapour

Dry vapour

Very wet vapour

15. An important characteristic of absorption system of refrigeration is

Noisy operation

Very little power consumption

Quiet operation

Cooling below 0°C

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

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

0.5

Zero

1.0

0.75

18. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

19. During dehumidification process, the relative humidity

Decreases

Remains constant

None of these

Increases

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

Depends on other factors

Increases

Remain same

Decreases

Page 3 of 4

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

All of these

R-12

Ammonia

CO₂

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

100

Zero

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

Suction of compressor

Low pressure side near receiver

Delivery of compressor

High pressure side close to receiver

24. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

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

Small displacements and low condensing pressures

Large displacements and low condensing pressures

Large displacements and high condensing pressures

Small displacements and high condensing pressures

27. During humidification process, dry bulb temperature

Remains constant

Increases

Decreases

None of these

28. 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

29. During sensible cooling of air ________ decreases.

Dry bulb temperature

Wet bulb temperature

Specific humidity

Relative humidity

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

More/less depending on size of plant

Less

Same

Page 4 of 4

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

Expansion valve

Compressor

Evaporator

Condenser

32. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

Cooling and dehumidification

Dehumidification

Heating and humidification

Humidification

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

Capillary tube

Electrically operated throttling valve

Thermostatic valve

Manually operated valve

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

Red

Yellow

Orange

Bright green

36. 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

Smaller cabinet should be used

Perfectly tight vapour seal should be used

Bigger cabinet should be used

37. The fluids used in Electrolux refrigerator are

Ammonia and hydrogen

Ammonia, water and hydrogen

None of these

Water and hydrogen

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

May increase or decrease depending on the type of refrigerant used

Decrease

Remain unaffected

Increase

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

Higher

Lower

Same

None of these

40. During sensible heating of air _________ decreases.

Wet bulb temperature

Dry bulb temperature

Relative humidity

Specific humidity

Refrigeration & Air-Conditioning Practice Set-1

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