Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

1. During sensible cooling of air, specific humidity

Decreases

Remains constant

None of these

Increases

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

Condenser

None of these

Absorber

Evaporator

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

Isentropic expansion process

Constant pressure expansion process

Constant pressure cooling process

Isentropic compression process

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

Carbon dioxide

Sulphur dioxide

R-12

Ammonia

5. Air refrigerator works on

None of these

Both (A) and (B)

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

6. 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

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

1 + B.P.F.

B.P.F. - 1

1 - B.P.F.

1/ B.P.F.

8. A refrigerant with the highest critical pressure is

R-11

Ammonia

R-22

R-12

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

Compressor

Expansion valve

Condenser

Evaporator

10. 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

Page 2 of 4

11. The specific humidity during humidification process

None of these

Increases

Decreases

Remains constant

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

Same

Very low

Low

High

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

Expansion

Evaporation

Condensation

Compression

14. 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

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

None of the above

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

Between compressor and condenser

In evaporator

Between condenser and evaporator

Before expansion valve

17. The wet bulb temperature during sensible cooling of air

Decreases

None of these

Increases

Remains constant

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

None of these

Lower than

Higher than

Same as

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

Humidification

Dehumidification

Cooling and dehumidification

Heating and humidification

20. A refrigerant compressor is used to

Raise the temperature of the refrigerant

All of the above

Raise the pressure of the refrigerant

Circulate the refrigerant through the refrigerating system

Page 3 of 4

21. 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

Heated and humidified

Cooled and dehumidified

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

Reciprocating

Centrifugal

Screw

Rotating

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

Sulphur dioxide

R-12

Ammonia

Carbon dioxide

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Specific humidity

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

Condenser to the expansion valve

Condenser to the evaporator

Evaporator to the thermostat

Expansion valve to the evaporator

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

Specific humidity

Dry bulb temperature

Wet bulb temperature

Dew point temperature

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

8°C

5°C

22°C

14°C

28. 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

29. The relative coefficient of performance is equal to

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

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

None of these

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

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

Dew point depression

Degree of saturation

Wet bulb depression

Dry bulb depression

Page 4 of 4

31. 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

Condenser

Expansion valve

32. Moisture should be removed from refrigerants to avoid

All of these

Corrosion of steel plates

Restriction to refrigerant flow

Freezing at the expansion valve

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

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

Horizontal and uniformly spaced

Curved lines

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

None of these

Higher

Lower

Same

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

Vertical line

Horizontal line

Curved line

Inclined line

36. The undesirable property of a refrigerant is

Non-toxic

High boiling point

Non-explosive

Non-flammable

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

Zero

Positive

None of these

Negative

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

Halide torch

Sulphur sticks

Soap and water

All of these

Refrigeration & Air-Conditioning Practice Set-7

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