Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Specific humidity

Wet bulb temperature

Dew point temperature

Dry bulb temperature

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

Heating and humidification

Cooling and dehumidification

Humidification

Dehumidification

3. 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

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

High

Very low

Same

Low

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

Rotating

Reciprocating

Screw

Centrifugal

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

Horizontal line

Inclined line

Vertical line

Curved line

8. 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 humidified

Cooled and dehumidified

Heated and humidified

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

Between condenser and evaporator

Before expansion valve

In evaporator

Between compressor and condenser

10. 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

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

14°C

8°C

5°C

22°C

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

Condensation

Compression

Evaporation

Expansion

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

1/ B.P.F.

1 + B.P.F.

1 - B.P.F.

B.P.F. - 1

14. During sensible cooling of air, specific humidity

Remains constant

Decreases

Increases

None of these

15. The specific humidity during humidification process

Decreases

Increases

None of these

Remains constant

16. 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

Evaporator

Expansion valve

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

Condenser

Evaporator

None of these

Absorber

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

Same

Lower

Higher

None of these

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

Degree of saturation

Dry bulb depression

Dew point depression

Wet bulb depression

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

Expansion valve to the evaporator

Evaporator to the thermostat

Condenser to the evaporator

Condenser to the expansion valve

Page 3 of 4

21. 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.)

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

Sulphur dioxide

Ammonia

R-12

Carbon dioxide

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

Condenser

Compressor

Evaporator

Expansion valve

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

After leaving the compressor

After leaving the condenser

Before entering the compressor

Before entering the condenser

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

R-12

Sulphur dioxide

Ammonia

Carbon dioxide

26. A refrigerant with the highest critical pressure is

Ammonia

R-11

R-22

R-12

27. The wet bulb temperature during sensible cooling of air

None of these

Increases

Remains constant

Decreases

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

Sulphur sticks

Soap and water

All of these

Halide torch

29. Moisture should be removed from refrigerants to avoid

Corrosion of steel plates

Freezing at the expansion valve

All of these

Restriction to refrigerant flow

30. Air refrigerator works on

(b) Bell Coleman cycle

None of these

(a) Reversed Carnot cycle

Both (A) and (B)

Page 4 of 4

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

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Specific humidity

32. The undesirable property of a refrigerant is

Non-toxic

Non-explosive

High boiling point

Non-flammable

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

Higher than

Lower than

None of these

Same as

34. 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

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

Zero

None of these

Positive

Negative

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

Horizontal and non-uniformly spaced

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

Constant pressure expansion process

Constant pressure cooling process

Isentropic expansion process

Isentropic compression process

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

It leads to significant cost reduction

The positive work in isentropic expansion of liquid is very small

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

It considerably reduces mass of the system

Refrigeration & Air-Conditioning Practice Set-7

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