Refrigeration & Air-Conditioning Practice Set-1

May 16, 2021

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1. The refrigerant widely used in domestic refrigerators is

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion throttle valve

Before entering the expansion valve

3. 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

4. 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

Bigger cabinet should be used

Perfectly tight vapour seal should be used

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

Compressor

Expansion valve

Condenser

Evaporator

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

None of these

Lower

Same

Higher

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

Cooling and dehumidification

Heating and humidification

Dehumidification

Humidification

8. The vapour pressure of refrigerant should be

Lower than atmospheric pressure

Equal to atmospheric pressure

Higher than atmospheric pressure

Could be anything

9. During humidification process, __________ increases.

Specific humidity

Relative humidity

Wet bulb temperature

Dry bulb temperature

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

Less

More/less depending on size of plant

Same

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

Bright green

Red

Yellow

Orange

12. Chaperon equation is a relation between

Specific volume and enthalpy

Temperature and enthalpy

Temperature, pressure, specific volume and enthalpy

Temperature, pressure and enthalpy

13. One ton refrigeration corresponds to

50 kcal/ min

80 kcal/ min

50 kcal/ hr

80 kcal/ hr

14. The reduced ambient air cooling system has

Two cooling turbines and two heat exchangers

One cooling turbine and one heat exchanger

One cooling turbine and two heat exchangers

Two cooling turbines and one heat exchanger

15. The moisture in a refrigerant is removed by

Evaporator

Driers

Safety relief valve

Dehumidifier

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

Electrically operated throttling valve

Manually operated valve

Thermostatic valve

Capillary tube

17. The fluids used in Electrolux refrigerator are

None of these

Ammonia, water and hydrogen

Ammonia and hydrogen

Water and hydrogen

18. 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

19. An important characteristic of absorption system of refrigeration is

Quiet operation

Noisy operation

Cooling below 0°C

Very little power consumption

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

R-12

CO₂

All of these

Ammonia

Page 3 of 4

21. During sensible heating of air _________ decreases.

Wet bulb temperature

Relative humidity

Specific humidity

Dry bulb temperature

22. Absorption system normally uses the following refrigerant

CO2

Ammonia

Freon-11

Freon-22

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

Using reagents

Smelling

Halide torch which on detection produces greenish flame lighting

Sulphur sticks which on detection gives white smoke

24. During sensible cooling of air ________ decreases.

Relative humidity

Dry bulb temperature

Specific humidity

Wet bulb temperature

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

High pressure saturated liquid

Wet vapour

Very wet vapour

Dry vapour

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

0.5

1.0

0.75

Zero

27. Which of the following statement is correct?

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

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

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

28. 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

29. 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

Relative humidity

Absolute humidity

Humidity ratio

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

Remain unaffected

Decrease

Increase

May increase or decrease depending on the type of refrigerant used

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31. 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 low condensing pressures

Large displacements and high condensing pressures

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

Evaporator

Condenser

Compressor

Expansion valve

33. 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.

34. Pick up the incorrect statement

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

Lithium bromide plant can't operate below 0°C

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

100

Zero

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

Decreases

Increases

Remains constant

None of these

38. During dehumidification process, the relative humidity

Remains constant

None of these

Increases

Decreases

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

40. 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

None of these

Dry bulb temperature

Wet bulb temperature

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