Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

1. Air refrigerator works on

(b) Bell Coleman cycle

Both (A) and (B)

None of these

(a) Reversed Carnot cycle

2. 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

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

Wet bulb temperature

Specific humidity

Dew point temperature

Dry bulb temperature

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

It leads to significant cost reduction

The positive work in isentropic expansion of liquid is very small

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

14°C

22°C

8°C

5°C

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

7. The undesirable property of a refrigerant is

High boiling point

Non-toxic

Non-explosive

Non-flammable

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

Carbon dioxide

R-12

Ammonia

Sulphur dioxide

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

Same as

Lower than

Higher than

None of these

10. 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.

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11. A refrigerant compressor is used to

Circulate the refrigerant through the refrigerating system

Raise the temperature of the refrigerant

Raise the pressure of the refrigerant

All of the above

12. The specific humidity during humidification process

Increases

Decreases

None of these

Remains constant

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

Evaporator to the thermostat

Condenser to the expansion valve

Expansion valve to the evaporator

Condenser to the evaporator

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

Cooling and dehumidification

Humidification

Dehumidification

Heating and humidification

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

Constant pressure expansion process

Constant pressure cooling process

Isentropic compression process

Isentropic expansion process

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

Between condenser and evaporator

Between compressor and condenser

Before expansion valve

In evaporator

17. 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.)

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

Dry bulb depression

Degree of saturation

Dew point depression

Wet bulb depression

19. During sensible cooling of air, specific humidity

Remains constant

Decreases

Increases

None of these

20. 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

Page 3 of 4

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

Soap and water

Halide torch

All of these

Sulphur sticks

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

Condensation

Evaporation

Expansion

Compression

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

Condenser

Absorber

Evaporator

None of these

24. A refrigerant with the highest critical pressure is

Ammonia

R-22

R-12

R-11

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

Negative

Zero

None of these

Positive

26. The wet bulb temperature during sensible cooling of air

None of these

Increases

Decreases

Remains constant

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

Vertical and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

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

Curved line

Inclined line

Horizontal line

Vertical line

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

Expansion valve

Condenser

Evaporator

Compressor

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

Wet bulb temperature

Dew point temperature

Specific humidity

Dry bulb temperature

Page 4 of 4

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

Low

High

Same

Very low

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

Same

Higher

None of these

Lower

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

Rotating

Reciprocating

Screw

Centrifugal

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

None of the above

It is not affected by the moisture present in the air

Its bulb is surrounded by a wet cloth exposed to the air

The moisture present in it begins to condense

35. 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

Condenser

Compressor

Expansion valve

36. 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

4

3

1/3

1/4

37. Moisture should be removed from refrigerants to avoid

Corrosion of steel plates

All of these

Restriction to refrigerant flow

Freezing at the expansion valve

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

After leaving the compressor

After leaving the condenser

Before entering the condenser

Before entering the compressor

Refrigeration & Air-Conditioning Practice Set-7

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