Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

1. 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

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

Compression

Condensation

Evaporation

Expansion

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

Higher than

None of these

Lower than

Same as

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

Dry bulb temperature

Wet bulb temperature

Specific humidity

Dew point temperature

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

Specific humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

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

Centrifugal

Screw

Rotating

Reciprocating

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

It leads to significant cost reduction

It considerably reduces mass of the system

The positive work in isentropic expansion of liquid is very small

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

9. The relative coefficient of performance is equal to

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

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

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

None of these

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

Curved line

Inclined line

Vertical line

Horizontal line

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

Positive

Negative

None of these

Zero

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

Condenser to the expansion valve

Evaporator to the thermostat

Condenser to the evaporator

Expansion valve to the evaporator

14. Moisture should be removed from refrigerants to avoid

All of these

Restriction to refrigerant flow

Corrosion of steel plates

Freezing at the expansion valve

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

22°C

14°C

5°C

8°C

16. 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.

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

Humidification

Cooling and dehumidification

Heating and humidification

Dehumidification

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

Sulphur dioxide

R-12

Carbon dioxide

Ammonia

19. The specific humidity during humidification process

Increases

Decreases

None of these

Remains constant

20. The undesirable property of a refrigerant is

Non-flammable

High boiling point

Non-explosive

Non-toxic

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

Constant pressure cooling process

Constant pressure expansion process

Isentropic compression process

Isentropic expansion process

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

High

Low

Very low

Same

23. The wet bulb temperature during sensible cooling of air

Remains constant

Increases

None of these

Decreases

24. 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

Cooled and dehumidified

Heated and humidified

Cooled and humidified

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

Lower

None of these

Higher

Same

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

Compressor

Evaporator

Condenser

Expansion valve

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

Before expansion valve

Between compressor and condenser

Between condenser and evaporator

In evaporator

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

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

The moisture present in it begins to condense

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

Condenser

None of these

Absorber

Evaporator

30. 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

3

1/3

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

1 + B.P.F.

1/ B.P.F.

B.P.F. - 1

1 - B.P.F.

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

Sulphur dioxide

Carbon dioxide

Ammonia

R-12

33. Air refrigerator works on

(b) Bell Coleman cycle

None of these

Both (A) and (B)

(a) Reversed Carnot cycle

34. A refrigerant with the highest critical pressure is

Ammonia

R-11

R-12

R-22

35. During sensible cooling of air, specific humidity

Remains constant

None of these

Increases

Decreases

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

Sulphur sticks

Soap and water

All of these

Halide torch

37. A refrigerant compressor is used to

Circulate the refrigerant through the refrigerating system

Raise the temperature of the refrigerant

All of the above

Raise the pressure of the refrigerant

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

Dew point depression

Dry bulb depression

Wet bulb depression

Degree of saturation

Refrigeration & Air-Conditioning Practice Set-7

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