Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

1 - C.O.P.

1 + (1/C.O.P)

1 + C.O.P

1 - (1/C.O.P)

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

5°C

22°C

14°C

8°C

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

Low

High

Very low

Same

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

Curved line

Vertical line

Inclined line

Horizontal line

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

Constant pressure cooling process

Constant pressure expansion process

Isentropic compression process

Isentropic expansion process

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

Wet bulb temperature

Dew point temperature

Dry bulb temperature

Specific humidity

7. Moisture should be removed from refrigerants to avoid

Restriction to refrigerant flow

Corrosion of steel plates

Freezing at the expansion valve

All of these

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

Sulphur dioxide

Carbon dioxide

R-12

Ammonia

9. 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.

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

Rotating

Reciprocating

Centrifugal

Screw

Page 2 of 4

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

Dry bulb depression

Degree of saturation

Wet bulb depression

Dew point depression

12. 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

The positive work in isentropic expansion of liquid is very small

It leads to significant cost reduction

It considerably reduces mass of the system

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

Zero

None of these

Positive

Negative

14. Air refrigerator works on

None of these

(a) Reversed Carnot cycle

(b) Bell Coleman cycle

Both (A) and (B)

15. 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

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

Compression

Condensation

Expansion

Evaporation

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

Soap and water

Halide torch

All of these

Sulphur sticks

18. During sensible cooling of air, specific humidity

None of these

Remains constant

Increases

Decreases

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

Specific humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

20. The wet bulb temperature during sensible cooling of air

Increases

None of these

Decreases

Remains constant

Page 3 of 4

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

Horizontal and non-uniformly spaced

Curved lines

Horizontal and uniformly spaced

Vertical and uniformly spaced

22. 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

Heated and dehumidified

Cooled and humidified

Heated and humidified

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

The moisture present in it begins to condense

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

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

Humidification

Dehumidification

Heating and humidification

Cooling and dehumidification

25. 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.)

26. The specific humidity during humidification process

None of these

Increases

Decreases

Remains constant

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

Absorber

None of these

Evaporator

Condenser

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

29. 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

30. The undesirable property of a refrigerant is

Non-flammable

Non-explosive

High boiling point

Non-toxic

Page 4 of 4

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

Evaporator

Compressor

Expansion valve

Condenser

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

Lower

None of these

Same

Higher

33. A refrigerant with the highest critical pressure is

R-11

R-22

R-12

Ammonia

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

1/4

1/3

4

3

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.

Expansion valve

Condenser

Compressor

Evaporator

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

Lower than

None of these

Same as

Higher than

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

Before expansion valve

Between condenser and evaporator

In evaporator

Between compressor and condenser

38. 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

Refrigeration & Air-Conditioning Practice Set-7

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