Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

1 + C.O.P

1 + (1/C.O.P)

1 - (1/C.O.P)

1 - C.O.P.

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

Dehumidification

Cooling and dehumidification

Humidification

Heating and humidification

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

None of these

Zero

Positive

Negative

4. 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

The positive work in isentropic expansion of liquid is very small

It leads to significant cost reduction

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

Dew point temperature

Wet bulb temperature

Specific humidity

Dry bulb temperature

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

Constant pressure cooling process

Isentropic compression process

Isentropic expansion process

Constant pressure expansion process

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

Before entering the compressor

After leaving the compressor

Before entering the condenser

After leaving the condenser

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

Between compressor and condenser

Between condenser and evaporator

Before expansion valve

In evaporator

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

Dew point depression

Degree of saturation

Dry bulb depression

Wet bulb depression

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

Inclined line

Vertical line

Curved line

Horizontal line

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

The moisture present in it begins to condense

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

12. A refrigerant compressor is used to

Raise the pressure of the refrigerant

Raise the temperature of the refrigerant

All of the above

Circulate the refrigerant through the refrigerating system

13. 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.

14. Air refrigerator works on

(b) Bell Coleman cycle

None of these

(a) Reversed Carnot cycle

Both (A) and (B)

15. The undesirable property of a refrigerant is

High boiling point

Non-flammable

Non-explosive

Non-toxic

16. The wet bulb temperature during sensible cooling of air

Increases

None of these

Decreases

Remains constant

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

None of these

Lower

Same

Higher

18. The relative coefficient of performance is equal to

None of these

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

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

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

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

Centrifugal

Rotating

Reciprocating

Screw

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

High

Same

Very low

Low

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

Curved lines

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

22. During sensible cooling of air, specific humidity

None of these

Remains constant

Increases

Decreases

23. 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

3

1/4

4

1/3

24. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Restriction to refrigerant flow

Corrosion of steel plates

All of these

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

Specific humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

26. 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

Expansion valve

Evaporator

Condenser

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

None of these

Absorber

Evaporator

Condenser

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

Condensation

Compression

Evaporation

Expansion

29. 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 humidified

Heated and dehumidified

Cooled and dehumidified

Cooled and humidified

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

None of these

Higher than

Lower than

Same as

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

Expansion valve to the evaporator

Condenser to the evaporator

Evaporator to the thermostat

Condenser to the expansion valve

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

Compressor

Expansion valve

Evaporator

Condenser

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

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

14°C

22°C

5°C

8°C

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

R-12

Sulphur dioxide

Carbon dioxide

Ammonia

36. A refrigerant with the highest critical pressure is

R-12

R-11

Ammonia

R-22

37. The specific humidity during humidification process

Increases

None of these

Decreases

Remains constant

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

Sulphur sticks

All of these

Soap and water

Halide torch

Refrigeration & Air-Conditioning Practice Set-7

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