Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Vertical and uniformly spaced

Curved lines

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

Dehumidification

Heating and humidification

Cooling and dehumidification

Humidification

3. Air refrigerator works on

(a) Reversed Carnot cycle

Both (A) and (B)

None of these

(b) Bell Coleman cycle

4. The wet bulb temperature during sensible cooling of air

Increases

None of these

Decreases

Remains constant

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

Lower than

None of these

Higher than

Same as

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

Evaporator

Compressor

Expansion valve

Condenser

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

Dew point temperature

Dry bulb temperature

Specific humidity

Wet bulb temperature

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

Condenser to the evaporator

Condenser to the expansion valve

Evaporator to the thermostat

Expansion valve to the evaporator

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

Evaporation

Condensation

Compression

Expansion

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

Soap and water

Halide torch

All of these

Sulphur sticks

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

12. The undesirable property of a refrigerant is

Non-explosive

Non-flammable

Non-toxic

High boiling point

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

Specific humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

14. The specific humidity during humidification process

Increases

Remains constant

None of these

Decreases

15. 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

None of the above

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

Between condenser and evaporator

In evaporator

Between compressor and condenser

Before expansion valve

17. 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

18. During sensible cooling of air, specific humidity

Increases

Remains constant

Decreases

None of these

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

Rotating

Centrifugal

Reciprocating

Screw

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

B.P.F. - 1

1/ B.P.F.

1 + B.P.F.

1 - B.P.F.

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21. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Corrosion of steel plates

Restriction to refrigerant flow

All of these

22. 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

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

1 - C.O.P.

1 + (1/C.O.P)

1 + C.O.P

1 - (1/C.O.P)

24. A refrigerant with the highest critical pressure is

R-12

R-22

R-11

Ammonia

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

22°C

8°C

14°C

5°C

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

Constant pressure cooling process

Isentropic compression process

Constant pressure expansion process

Isentropic expansion process

27. The relative coefficient of performance is equal to

None of these

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

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

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

28. 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

3

4

1/4

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

It considerably reduces mass of the system

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

It leads to significant cost reduction

The positive work in isentropic expansion of liquid is very small

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

None of these

Negative

Zero

Positive

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31. 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.

Evaporator

Condenser

Expansion valve

Compressor

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

Same

None of these

Lower

Higher

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

34. 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

Cooled and humidified

Heated and humidified

Heated and dehumidified

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

Same

Low

High

Very low

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

None of these

Evaporator

Condenser

Absorber

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

Curved line

Vertical line

Horizontal line

Inclined line

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

Degree of saturation

Dew point depression

Wet bulb depression

Dry bulb depression

Refrigeration & Air-Conditioning Practice Set-7

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