Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. Which of the following statement is wrong?

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

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.

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

2. Under cooling in a refrigeration cycle

Decreases C.O.P

Increases C.O.P

C.O.P remains unaltered

Other factors decide C.O.P

3. The moisture in a refrigerant is removed by

Driers

Evaporator

Safety relief valve

Dehumidifier

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

1.0

0.5

Zero

0.75

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

Bigger cabinet should be used

Perfectly tight vapour seal should be used

Refrigerant with lower evaporation temperature should be used

Smaller cabinet should be used

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

Using reagents

Halide torch which on detection produces greenish flame lighting

Sulphur sticks which on detection gives white smoke

Smelling

7. During dehumidification process, the relative humidity

None of these

Increases

Remains constant

Decreases

8. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Could be anything

Higher than atmospheric pressure

Equal to atmospheric pressure

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

Thermostatic valve

Capillary tube

Electrically operated throttling valve

Manually operated valve

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

Evaporator

Condenser

Expansion valve

Compressor

Page 2 of 4

11. 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

Absolute humidity

Degree of saturation

Relative humidity

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

Red

Yellow

Bright green

Orange

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

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion throttle valve

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

Lower

Higher

None of these

Same

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

Delivery of compressor

Low pressure side near receiver

Suction of compressor

High pressure side close to receiver

16. One ton refrigeration corresponds to

80 kcal/ hr

50 kcal/ hr

50 kcal/ min

80 kcal/ min

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

Same

Less

More/less depending on size of plant

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

R-12

All of these

CO₂

Ammonia

19. 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 high condensing pressures

Large displacements and low condensing pressures

20. An important characteristic of absorption system of refrigeration is

Noisy operation

Very little power consumption

Quiet operation

Cooling below 0°C

Page 3 of 4

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

100

Zero

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

Saturated liquid

Dry saturated vapour

Wet vapour

Superheated vapour

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

Heating and humidification

Cooling and dehumidification

Dehumidification

Humidification

24. The fluids used in Electrolux refrigerator are

None of these

Ammonia, water and hydrogen

Ammonia and hydrogen

Water and hydrogen

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

Expansion valve

Evaporator

Condenser

Compressor

26. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

One cooling turbine and one heat exchanger

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

27. Absorption system normally uses the following refrigerant

Ammonia

Freon-22

CO2

Freon-11

28. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature, pressure, specific volume and enthalpy

Specific volume and enthalpy

Temperature and enthalpy

29. During sensible heating of air _________ decreases.

Relative humidity

Wet bulb temperature

Specific humidity

Dry bulb temperature

30. During humidification process, __________ increases.

Relative humidity

Specific humidity

Dry bulb temperature

Wet bulb temperature

Page 4 of 4

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

Wet vapour

Dry vapour

High pressure saturated liquid

Very wet vapour

32. 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.

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

33. During sensible cooling of air ________ decreases.

Dry bulb temperature

Wet bulb temperature

Relative humidity

Specific humidity

34. 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

Increase

Remain unaffected

35. The refrigerant widely used in domestic refrigerators is

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

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

Decreases

Remain same

Increases

Depends on other factors

37. During humidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

38. Pick up the incorrect statement

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

Lithium bromide used in vapour absorption cycle is non volatile

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

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

24 bars

Slightly above atmospheric pressure

Atmospheric pressure

56 bars

40. The temperature of air recorded by a thermometer, when it is not affected by the moisture present in the air, is called

Wet bulb temperature

None of these

Dew point temperature

Dry bulb temperature

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Refrigeration & Air-Conditioning Practice Set-1

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