Refrigeration & Air-Conditioning Practice Set-7

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1. 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

4

1/4

1/3

3

2. The specific humidity during humidification process

Increases

Decreases

Remains constant

None of these

3. Air refrigerator works on

(a) Reversed Carnot cycle

None of these

Both (A) and (B)

(b) Bell Coleman cycle

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

None of the above

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

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

Rotating

Screw

Reciprocating

Centrifugal

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

7. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Restriction to refrigerant flow

All of these

Corrosion of steel plates

8. During sensible cooling of air, specific humidity

None of these

Remains constant

Increases

Decreases

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

Ammonia

R-12

Sulphur dioxide

Carbon dioxide

10. 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.

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11. The undesirable property of a refrigerant is

High boiling point

Non-flammable

Non-toxic

Non-explosive

12. 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 humidified

Cooled and dehumidified

Heated and dehumidified

Heated and humidified

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

Same

None of these

Lower

Higher

14. A refrigerant with the highest critical pressure is

R-22

Ammonia

R-11

R-12

15. The relative coefficient of performance is equal to

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

None of these

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

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

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

Specific humidity

Dry bulb temperature

Dew point temperature

Wet bulb temperature

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

Sulphur sticks

Halide torch

Soap and water

All of these

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

Before expansion valve

Between condenser and evaporator

In evaporator

Between compressor and condenser

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

Expansion valve

Compressor

Condenser

Evaporator

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

Before entering the compressor

Before entering the condenser

After leaving the condenser

After leaving the compressor

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

Higher than

Same as

None of these

Lower than

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

None of these

Positive

Zero

Negative

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

1/ B.P.F.

1 - B.P.F.

1 + B.P.F.

B.P.F. - 1

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

Same

Low

Very low

High

25. 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

It considerably reduces mass of the system

It leads to significant cost reduction

The positive work in isentropic expansion of liquid is very small

26. A refrigerant compressor is used to

Raise the pressure of the refrigerant

Raise the temperature of the refrigerant

Circulate the refrigerant through the refrigerating system

All of the above

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

Wet bulb depression

Degree of saturation

Dry bulb depression

Dew point depression

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

Condenser to the expansion valve

Condenser to the evaporator

Expansion valve to the evaporator

Evaporator to the thermostat

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

None of these

Condenser

Absorber

Evaporator

30. 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.

Compressor

Evaporator

Expansion valve

Condenser

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

Inclined line

Vertical line

Horizontal line

Curved line

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

5°C

8°C

22°C

14°C

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

Expansion

Condensation

Evaporation

Compression

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

Cooling and dehumidification

Heating and humidification

Dehumidification

Humidification

36. The wet bulb temperature during sensible cooling of air

Decreases

Remains constant

None of these

Increases

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

Isentropic expansion process

Constant pressure expansion process

Isentropic compression process

Constant pressure cooling process

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

Specific humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Refrigeration & Air-Conditioning Practice Set-7

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