Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

1. The relative coefficient of performance is equal to

(Theoretical C.O.P.)/ (Actual C.O.P.)

(Actual C.O.P.) × (Theoretical C.O.P.)

(Actual C.O.P.) /(Theoretical C.O.P.)

None of these

2. A refrigerant with the highest critical pressure is

Ammonia

R-11

R-12

R-22

3. The central air conditioning system has ___________ overall efficiency as compared to individual systems.

Same

None of these

Higher

Lower

4. The wet bulb temperature at 100% relative humidity is ________ dry bulb temperature.

Higher than

Same as

None of these

Lower than

5. The wet bulb temperature during sensible cooling of air

Decreases

None of these

Remains constant

Increases

6. Wet bulb temperature is the temperature of air recorded by a thermometer, when

None of the above

The moisture present in it begins to condense

It is not affected by the moisture present in the air

Its bulb is surrounded by a wet cloth exposed to the air

7. The process, generally used in summer air conditioning to cool and dehumidify the air, is called

Dehumidification

Heating and humidification

Humidification

Cooling and dehumidification

8. The undesirable property of a refrigerant is

Non-explosive

Non-toxic

Non-flammable

High boiling point

9. Air refrigerator works on

None of these

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

Both (A) and (B)

10. Moisture should be removed from refrigerants to avoid

Restriction to refrigerant flow

Freezing at the expansion valve

Corrosion of steel plates

All of these

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11. During sensible cooling of air, specific humidity

Remains constant

Decreases

None of these

Increases

12. The lowest temperature during the cycle in a vapour compression system occurs after

Condensation

Expansion

Compression

Evaporation

13. The emissivity of a polished silver body is _________ as compared to black body.

Very low

Same

High

Low

14. The leakage in a refrigeration system using ammonia is detected by

Soap and water

Sulphur sticks

Halide torch

All of these

15. The horizontal and non-uniformly spaced lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Specific humidity

16. In mechanical refrigeration system, the refrigerant has the maximum temperature

Between condenser and evaporator

Between compressor and condenser

Before expansion valve

In evaporator

17. A condenser of refrigeration system rejects heat at the rate of 120 kW, while its compressor consumes a power of 30 kW. The coefficient of performance of the system will be

1/3

1/4

4

3

18. In a domestic refrigerator, a capillary tube controls the flow of refrigerant from the

Condenser to the evaporator

Expansion valve to the evaporator

Evaporator to the thermostat

Condenser to the expansion valve

19. When the air is passed through an insulated chamber having sprays of water maintained at a temperature higher than the dew point temperature of entering air but lower than its dry bulb temperature, then the air is said to be

Cooled and dehumidified

Heated and humidified

Heated and dehumidified

Cooled and humidified

20. Which of the following refrigerant is highly toxic and flammable?

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

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21. In case of sensible cooling of air, the coil efficiency is given by

1 + B.P.F.

B.P.F. - 1

1/ B.P.F.

1 - B.P.F.

22. The vertical and uniformly spaced lines on a psychrometric chart indicates

Specific humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

23. The refrigerant used in small tonnage commercial machines (hermetically sealed units) is

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

24. During a refrigeration cycle, heat is rejected by the refrigerant in a

Compressor

Expansion valve

Condenser

Evaporator

25. In a vapour compression system, the condition of refrigerant is dry saturated vapour

After leaving the compressor

Before entering the compressor

After leaving the condenser

Before entering the condenser

26. In a psychrometric chart, specific humidity (moisture content) lines are

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

27. The heat rejection factor (HRF) is given by

1 - (1/C.O.P)

1 - C.O.P.

1 + C.O.P

1 + (1/C.O.P)

28. For large tonnage (more than 200 TR) air-conditioning applications, the compressor recommended is

Rotating

Centrifugal

Reciprocating

Screw

29. A refrigerant compressor is used to

Raise the pressure of the refrigerant

Circulate the refrigerant through the refrigerating system

All of the above

Raise the temperature of the refrigerant

30. The human body feels comfortable when the heat stored in the body is

Negative

Zero

Positive

None of these

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31. In aqua ammonia absorption refrigeration system, incomplete rectification leads to accumulation of water in

Evaporator

None of these

Absorber

Condenser

32. The specific humidity during humidification process

Remains constant

None of these

Increases

Decreases

33. Most air cooled condensers are designed to operate with a temperature difference of

22°C

8°C

5°C

14°C

34. In order to collect liquid refrigerant and to prevent it from going to a ________, a device known as accumulator is used at the suction of compressor.

Expansion valve

Condenser

Evaporator

Compressor

35. In a vapour compression refrigeration system, a throttle valve is used in place of an expander because

It improves the C.O.P., as the condenser is small

The positive work in isentropic expansion of liquid is very small

It considerably reduces mass of the system

It leads to significant cost reduction

36. The dehumidification process, on the psychrometric chart, is shown by

Curved line

Horizontal line

Inclined line

Vertical line

37. In a reversed Brayton cycle, the heat is absorbed by the air during

Isentropic expansion process

Isentropic compression process

Constant pressure cooling process

Constant pressure expansion process

38. The difference between dry bulb temperature and dew point temperature, is called

Dew point depression

Degree of saturation

Wet bulb depression

Dry bulb depression

Refrigeration & Air-Conditioning Practice Set-7

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