Refrigeration & Air-Conditioning Practice Set-7

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1. 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

Heated and dehumidified

Heated and humidified

Cooled and humidified

Cooled and dehumidified

2. 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

1/4

4

1/3

3

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

Dry bulb temperature

Specific humidity

Wet bulb temperature

Dew point temperature

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

Between compressor and condenser

In evaporator

Between condenser and evaporator

Before expansion valve

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

Compressor

Evaporator

Condenser

Expansion valve

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

5°C

22°C

8°C

14°C

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

All of these

Halide torch

Soap and water

Sulphur sticks

8. 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)

9. A refrigerant compressor is used to

All of the above

Circulate the refrigerant through the refrigerating system

Raise the temperature of the refrigerant

Raise the pressure of the refrigerant

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

Expansion

Condensation

Evaporation

Compression

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11. Moisture should be removed from refrigerants to avoid

All of these

Restriction to refrigerant flow

Freezing at the expansion valve

Corrosion of steel plates

12. 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

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

14. The undesirable property of a refrigerant is

Non-flammable

Non-toxic

Non-explosive

High boiling point

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

Isentropic compression process

Constant pressure cooling process

Constant pressure expansion process

Isentropic expansion process

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

Higher than

Same as

Lower than

None of these

17. Air refrigerator works on

(a) Reversed Carnot cycle

(b) Bell Coleman cycle

None of these

Both (A) and (B)

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

Curved line

Vertical line

Horizontal line

Inclined line

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

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Vertical and uniformly spaced

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

It leads to significant cost reduction

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

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

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

The moisture present in it begins to condense

None of the above

It is not affected by the moisture present in the air

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

Wet bulb depression

Dew point depression

Degree of saturation

Dry bulb depression

23. A refrigerant with the highest critical pressure is

R-22

R-11

Ammonia

R-12

24. The specific humidity during humidification process

Increases

None of these

Decreases

Remains constant

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Zero

Negative

None of these

Positive

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

High

Same

Low

Very low

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

Centrifugal

Rotating

Screw

Reciprocating

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

None of these

Evaporator

Condenser

Absorber

30. During sensible cooling of air, specific humidity

Remains constant

None of these

Decreases

Increases

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

Condenser to the expansion valve

Expansion valve to the evaporator

Condenser to the evaporator

Evaporator to the thermostat

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

After leaving the condenser

Before entering the compressor

After leaving the compressor

Before entering the condenser

33. The wet bulb temperature during sensible cooling of air

Increases

Decreases

None of these

Remains constant

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

Heating and humidification

Dehumidification

Humidification

Cooling and dehumidification

35. The relative coefficient of performance is equal to

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

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

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

None of these

36. 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

Condenser

Expansion valve

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

None of these

Higher

Lower

Same

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

Specific humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Refrigeration & Air-Conditioning Practice Set-7

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