Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Expansion valve to the evaporator

Condenser to the expansion valve

Condenser to the evaporator

Evaporator to the thermostat

2. 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

Condenser

Expansion valve

Evaporator

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

4. 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 dehumidified

Cooled and humidified

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

Inclined line

Curved line

Vertical line

Horizontal line

6. The wet bulb temperature during sensible cooling of air

Increases

None of these

Decreases

Remains constant

7. The specific humidity during humidification process

Remains constant

Increases

Decreases

None of these

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

Sulphur dioxide

Ammonia

Carbon dioxide

R-12

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

Dew point depression

Dry bulb depression

Wet bulb depression

Degree of saturation

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

14°C

8°C

5°C

22°C

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11. 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

12. 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.

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

Wet bulb temperature

Dew point temperature

Specific humidity

Dry bulb temperature

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

Before entering the compressor

After leaving the compressor

After leaving the condenser

Before entering the condenser

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

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Specific humidity

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

Compressor

Evaporator

Condenser

Expansion valve

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

Halide torch

Soap and water

All of these

Sulphur sticks

18. A refrigerant with the highest critical pressure is

Ammonia

R-22

R-12

R-11

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

Reciprocating

Rotating

Centrifugal

Screw

20. 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 leads to significant cost reduction

It considerably reduces mass of the system

The positive work in isentropic expansion of liquid is very small

Page 3 of 4

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

In evaporator

Between compressor and condenser

Before expansion valve

Between condenser and evaporator

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

High

Low

Very low

Same

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

Zero

None of these

Positive

Negative

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Curved lines

Horizontal and uniformly spaced

25. The undesirable property of a refrigerant is

Non-toxic

Non-flammable

Non-explosive

High boiling point

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

Lower

None of these

Same

Higher

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

Higher than

Lower than

Same as

None of these

28. Moisture should be removed from refrigerants to avoid

All of these

Corrosion of steel plates

Freezing at the expansion valve

Restriction to refrigerant flow

29. 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

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

Compression

Evaporation

Expansion

Condensation

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

None of these

Condenser

Absorber

Evaporator

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

1 - C.O.P.

1 + C.O.P

1 - (1/C.O.P)

1 + (1/C.O.P)

33. During sensible cooling of air, specific humidity

Remains constant

Increases

None of these

Decreases

34. 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.)

35. 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

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

Cooling and dehumidification

Heating and humidification

Humidification

Dehumidification

37. Air refrigerator works on

Both (A) and (B)

(a) Reversed Carnot cycle

(b) Bell Coleman cycle

None of these

38. A refrigerant compressor is used to

Raise the temperature of the refrigerant

All of the above

Circulate the refrigerant through the refrigerating system

Raise the pressure of the refrigerant

Refrigeration & Air-Conditioning Practice Set-7

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