Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

B.P.F. - 1

1 - B.P.F.

1/ B.P.F.

1 + B.P.F.

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

Between condenser and evaporator

In evaporator

Between compressor and condenser

Before expansion valve

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

Before entering the condenser

Before entering the compressor

After leaving the condenser

After leaving the compressor

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

5. Air refrigerator works on

Both (A) and (B)

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

None of these

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

Lower than

Higher than

None of these

Same as

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

Compression

Evaporation

Expansion

Condensation

8. The undesirable property of a refrigerant is

Non-explosive

Non-flammable

High boiling point

Non-toxic

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

Curved line

Horizontal line

Vertical line

Inclined line

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

Dry bulb temperature

Dew point temperature

Wet bulb temperature

Specific humidity

Page 2 of 4

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

Negative

Zero

None of these

Positive

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

Heating and humidification

Humidification

Cooling and dehumidification

Dehumidification

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

Rotating

Screw

Centrifugal

Reciprocating

14. The relative coefficient of performance is equal to

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

None of these

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

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

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

Dry bulb temperature

Specific humidity

Dew point temperature

Wet bulb temperature

16. 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

The positive work in isentropic expansion of liquid is very small

It leads to significant cost reduction

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

Lower

Same

None of these

Higher

18. The wet bulb temperature during sensible cooling of air

Decreases

None of these

Increases

Remains constant

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

Dry bulb depression

Dew point depression

Wet bulb depression

Degree of saturation

20. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Restriction to refrigerant flow

All of these

Corrosion of steel plates

Page 3 of 4

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

Absorber

None of these

Condenser

Evaporator

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

Vertical and uniformly spaced

Horizontal and uniformly spaced

Curved lines

Horizontal and non-uniformly spaced

23. 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

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

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

None of the above

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

26. 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

Compressor

Condenser

Evaporator

27. 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)

28. A refrigerant with the highest critical pressure is

R-11

R-12

Ammonia

R-22

29. 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

1/4

1/3

3

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

Constant pressure expansion process

Isentropic expansion process

Constant pressure cooling process

Isentropic compression process

Page 4 of 4

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

22°C

14°C

5°C

8°C

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

Halide torch

Sulphur sticks

All of these

Soap and water

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

Condenser

Compressor

Evaporator

Expansion valve

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

Same

High

Low

Very low

35. 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 humidified

Heated and dehumidified

36. During sensible cooling of air, specific humidity

Decreases

None of these

Remains constant

Increases

37. 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

38. The specific humidity during humidification process

Increases

Remains constant

None of these

Decreases

Refrigeration & Air-Conditioning Practice Set-7

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