Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Horizontal line

Curved line

Vertical line

Inclined line

2. A refrigerant with the highest critical pressure is

R-11

Ammonia

R-12

R-22

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

Humidification

Heating and humidification

Cooling and dehumidification

Dehumidification

4. The specific humidity during humidification process

Decreases

Remains constant

Increases

None of these

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

R-12

Carbon dioxide

Ammonia

Sulphur dioxide

6. 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

Cooled and humidified

Heated and dehumidified

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

Constant pressure expansion process

Isentropic compression process

Constant pressure cooling process

Isentropic expansion process

8. The undesirable property of a refrigerant is

Non-explosive

High boiling point

Non-toxic

Non-flammable

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

1 - (1/C.O.P)

1 - C.O.P.

1 + (1/C.O.P)

1 + C.O.P

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

None of these

Same as

Higher than

Lower than

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11. Moisture should be removed from refrigerants to avoid

Corrosion of steel plates

Freezing at the expansion valve

Restriction to refrigerant flow

All of these

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

Low

High

Very low

Same

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

Wet bulb temperature

Dew point temperature

Specific humidity

Dry bulb temperature

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

Before expansion valve

Between condenser and evaporator

In evaporator

Between compressor and condenser

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

Screw

Reciprocating

Rotating

Centrifugal

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

8°C

14°C

22°C

5°C

17. 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

Evaporator

Condenser

Compressor

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

Lower

None of these

Same

Higher

19. 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

4

3

1/4

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

Compression

Expansion

Evaporation

Condensation

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

Evaporator to the thermostat

Condenser to the expansion valve

Expansion valve to the evaporator

Condenser to the evaporator

22. The wet bulb temperature during sensible cooling of air

Decreases

Remains constant

None of these

Increases

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

Expansion valve

Condenser

Evaporator

Compressor

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

Dew point depression

Dry bulb depression

Wet bulb depression

Degree of saturation

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

Negative

Zero

None of these

Positive

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

After leaving the compressor

After leaving the condenser

Before entering the compressor

Before entering the condenser

27. A refrigerant compressor is used to

Raise the pressure of the refrigerant

All of the above

Raise the temperature of the refrigerant

Circulate the refrigerant through the refrigerating system

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

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

Absorber

Evaporator

Condenser

None of these

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

Specific humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

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31. The relative coefficient of performance is equal to

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

None of these

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

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

32. During sensible cooling of air, specific humidity

None of these

Remains constant

Increases

Decreases

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

All of these

Sulphur sticks

Halide torch

Soap and water

34. 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

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

None of the above

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

37. 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.

38. Air refrigerator works on

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

None of these

Both (A) and (B)

Refrigeration & Air-Conditioning Practice Set-7

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