Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Evaporation

Compression

Expansion

Condensation

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.

Evaporator

Compressor

Expansion valve

Condenser

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

Centrifugal

Rotating

Reciprocating

Screw

4. A refrigerant with the highest critical pressure is

R-11

R-12

R-22

Ammonia

5. The undesirable property of a refrigerant is

Non-explosive

Non-flammable

High boiling point

Non-toxic

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

Negative

Zero

Positive

None of these

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

8. 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

9. Air refrigerator works on

Both (A) and (B)

(a) Reversed Carnot cycle

None of these

(b) Bell Coleman cycle

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

Sulphur sticks

Halide torch

All of these

Soap and water

Page 2 of 4

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

Condenser

Absorber

Evaporator

None of these

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

Isentropic compression process

Constant pressure cooling process

Isentropic expansion process

Constant pressure expansion process

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

14°C

5°C

8°C

22°C

14. The relative coefficient of performance is equal to

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

None of these

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

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

15. 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.

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

Dehumidification

Humidification

Cooling and dehumidification

Heating and humidification

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

Curved line

Vertical line

Horizontal line

Inclined line

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

Higher than

None of these

Lower than

Same as

19. 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

Cooled and dehumidified

Cooled and humidified

Heated and dehumidified

Heated and humidified

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Specific humidity

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

The moisture present in it begins to condense

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

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

Between condenser and evaporator

Before expansion valve

Between compressor and condenser

In evaporator

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

Dew point temperature

Specific humidity

Wet bulb temperature

Dry bulb temperature

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

Wet bulb depression

Degree of saturation

Dry bulb depression

Dew point depression

25. 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

1/3

4

3

1/4

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

It considerably reduces mass of the system

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

The positive work in isentropic expansion of liquid is very small

It leads to significant cost reduction

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

Low

Same

Very low

High

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

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

Horizontal and non-uniformly spaced

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

Carbon dioxide

Sulphur dioxide

Ammonia

R-12

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

After leaving the condenser

Before entering the condenser

After leaving the compressor

Before entering the compressor

Page 4 of 4

31. The wet bulb temperature during sensible cooling of air

Increases

None of these

Remains constant

Decreases

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

1 + (1/C.O.P)

1 - (1/C.O.P)

1 + C.O.P

1 - C.O.P.

33. A refrigerant compressor is used to

All of the above

Raise the temperature of the refrigerant

Raise the pressure of the refrigerant

Circulate the refrigerant through the refrigerating system

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

Condenser

Expansion valve

Compressor

Evaporator

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

Lower

None of these

Same

Higher

36. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Restriction to refrigerant flow

Corrosion of steel plates

All of these

37. The specific humidity during humidification process

Increases

None of these

Remains constant

Decreases

38. During sensible cooling of air, specific humidity

Increases

Decreases

None of these

Remains constant

Refrigeration & Air-Conditioning Practice Set-7

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