Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

1. Air refrigerator works on

None of these

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

Both (A) and (B)

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

Higher than

None of these

Lower than

Same as

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

Carbon dioxide

R-12

Sulphur dioxide

Ammonia

4. 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

It is not affected by the moisture present in the air

None of the above

The moisture present in it begins to condense

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

Same

Lower

None of these

Higher

6. A refrigerant compressor is used to

Raise the pressure of the refrigerant

Circulate the refrigerant through the refrigerating system

Raise the temperature of the refrigerant

All of the above

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

Very low

Same

Low

High

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

Condensation

Evaporation

Compression

Expansion

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

Curved line

Vertical line

Inclined line

Horizontal line

10. The wet bulb temperature during sensible cooling of air

Increases

None of these

Remains constant

Decreases

Page 2 of 4

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

Wet bulb temperature

Dew point temperature

Specific humidity

Dry bulb temperature

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

Condenser to the expansion valve

Expansion valve to the evaporator

Evaporator to the thermostat

Condenser to the evaporator

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

Humidification

Heating and humidification

Cooling and dehumidification

Dehumidification

14. The undesirable property of a refrigerant is

Non-toxic

Non-explosive

High boiling point

Non-flammable

15. 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

16. Moisture should be removed from refrigerants to avoid

All of these

Restriction to refrigerant flow

Corrosion of steel plates

Freezing at the expansion valve

17. During sensible cooling of air, specific humidity

Decreases

Remains constant

None of these

Increases

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

14°C

8°C

22°C

5°C

19. 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.

20. 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

1/3

4

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21. The relative coefficient of performance is equal to

None of these

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

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

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

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

Before expansion valve

In evaporator

Between condenser and evaporator

Between compressor and condenser

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

Absorber

Evaporator

Condenser

None of these

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

None of these

Positive

Negative

Zero

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

Halide torch

Soap and water

All of these

Sulphur sticks

26. The specific humidity during humidification process

Remains constant

Increases

None of these

Decreases

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

Constant pressure expansion process

Isentropic compression process

Isentropic expansion process

Constant pressure cooling process

28. 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

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

Cooled and dehumidified

Heated and dehumidified

Cooled and humidified

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

Wet bulb depression

Degree of saturation

Dry bulb depression

Dew point depression

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31. A refrigerant with the highest critical pressure is

R-11

Ammonia

R-12

R-22

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

Dew point temperature

Specific humidity

Dry bulb temperature

Wet bulb temperature

33. 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

34. 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

Compressor

Condenser

Expansion valve

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

Centrifugal

Rotating

Screw

Reciprocating

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

Condenser

Evaporator

Compressor

Expansion valve

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

Ammonia

Sulphur dioxide

R-12

Carbon dioxide

38. 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

Refrigeration & Air-Conditioning Practice Set-7

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