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.

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

In vapour compression cycle, the useful part of the heat transfer is at the condenser.

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

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

3. The fluids used in Electrolux refrigerator are

Ammonia, water and hydrogen

Ammonia and hydrogen

Water and hydrogen

None of these

4. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Higher than atmospheric pressure

Could be anything

Equal to atmospheric pressure

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

Condenser

Expansion valve

Compressor

Evaporator

6. During humidification process, dry bulb temperature

Decreases

None of these

Increases

Remains constant

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

Decreases

Increases

Remain same

Depends on other factors

8. 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

Perfectly tight vapour seal should be used

Bigger cabinet should be used

Smaller cabinet should be used

9. During dehumidification process, the relative humidity

Increases

Remains constant

None of these

Decreases

10. The refrigerant widely used in domestic refrigerators is

R-12

Carbon dioxide

Sulphur dioxide

Ammonia

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11. An important characteristic of absorption system of refrigeration is

Cooling below 0°C

Very little power consumption

Quiet operation

Noisy operation

12. Absorption system normally uses the following refrigerant

Freon-22

CO2

Ammonia

Freon-11

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

Evaporator

Compressor

Condenser

Expansion valve

14. Under cooling in a refrigeration cycle

Increases C.O.P

C.O.P remains unaltered

Decreases C.O.P

Other factors decide C.O.P

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

Capillary tube

Electrically operated throttling valve

Manually operated valve

Thermostatic valve

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

More/less depending on size of plant

Less

Same

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

None of these

Same

Higher

Lower

18. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Dry bulb temperature

Specific humidity

19. Chaperon equation is a relation between

Temperature, pressure and enthalpy

Temperature and enthalpy

Specific volume and enthalpy

Temperature, pressure, specific volume and enthalpy

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

Before entering the expansion valve

After passing through the expansion throttle valve

Before passing through the condenser

After passing through the condenser

Page 3 of 4

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

Dry vapour

Wet vapour

High pressure saturated liquid

Very wet vapour

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

Slightly above atmospheric pressure

Atmospheric pressure

56 bars

24 bars

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

Remain unaffected

Increase

Decrease

May increase or decrease depending on the type of refrigerant used

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

Sulphur sticks which on detection gives white smoke

Using reagents

Smelling

Halide torch which on detection produces greenish flame lighting

25. The moisture in a refrigerant is removed by

Evaporator

Safety relief valve

Dehumidifier

Driers

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

100

Zero

27. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ min

50 kcal/ hr

80 kcal/ hr

28. The reduced ambient air cooling system has

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

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

Cooling and dehumidification

Humidification

Heating and humidification

Dehumidification

30. 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.

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

Red

Orange

Bright green

Yellow

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

Large displacements and low condensing pressures

Small displacements and high condensing pressures

Small displacements and low condensing pressures

Large displacements and high condensing pressures

33. 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

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

1.0

Zero

0.5

0.75

35. 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

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

36. During humidification process, __________ increases.

Wet bulb temperature

Dry bulb temperature

Relative humidity

Specific humidity

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

Ammonia

All of these

R-12

CO₂

38. 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

Wet bulb temperature

Dew point temperature

None of these

39. During sensible cooling of air ________ decreases.

Relative humidity

Wet bulb temperature

Dry bulb temperature

Specific humidity

40. 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

Degree of saturation

Absolute humidity

Relative humidity

Humidity ratio

Refrigeration & Air-Conditioning Practice Set-1

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