Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Inclined line

Vertical line

Curved line

Horizontal line

2. The wet bulb temperature during sensible cooling of air

Increases

Remains constant

None of these

Decreases

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

Between compressor and condenser

In evaporator

Before expansion valve

Between condenser and evaporator

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

Reciprocating

Rotating

Centrifugal

Screw

5. 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

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

All of these

Sulphur sticks

Soap and water

Halide torch

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

Wet bulb temperature

Specific humidity

Dry bulb temperature

Dew point temperature

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

Ammonia

Carbon dioxide

R-12

Sulphur dioxide

9. During sensible cooling of air, specific humidity

Decreases

None of these

Increases

Remains constant

10. 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 humidified

Heated and humidified

Cooled and dehumidified

Heated and dehumidified

Page 2 of 4

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

Horizontal and non-uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and uniformly spaced

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

Dew point depression

Dry bulb depression

Wet bulb depression

Degree of saturation

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

Evaporator to the thermostat

Expansion valve to the evaporator

Condenser to the evaporator

Condenser to the expansion valve

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

22°C

8°C

14°C

5°C

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

Compression

Expansion

Condensation

Evaporation

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

Same

Lower

Higher

None of these

17. The undesirable property of a refrigerant is

Non-toxic

Non-explosive

High boiling point

Non-flammable

18. The specific humidity during humidification process

Increases

Remains constant

None of these

Decreases

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

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

Dehumidification

Humidification

Cooling and dehumidification

Heating and humidification

Page 3 of 4

21. 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.)

22. 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.

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

Isentropic expansion process

Constant pressure cooling process

Constant pressure expansion process

Isentropic compression process

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

Wet bulb temperature

Specific humidity

Dew point temperature

Dry bulb temperature

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

None of these

Lower than

Same as

Higher than

26. Air refrigerator works on

Both (A) and (B)

(a) Reversed Carnot cycle

(b) Bell Coleman cycle

None of these

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

Before entering the condenser

After leaving the condenser

Before entering the compressor

After leaving the compressor

28. Moisture should be removed from refrigerants to avoid

Restriction to refrigerant flow

Corrosion of steel plates

All of these

Freezing at the expansion valve

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

Zero

Positive

None of these

Negative

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

It is not affected by the moisture present in the air

None of the above

The moisture present in it begins to condense

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

Page 4 of 4

31. 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

3

1/3

4

32. 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)

33. A refrigerant with the highest critical pressure is

R-12

R-22

Ammonia

R-11

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

Very low

High

Low

Same

35. 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

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

It leads to significant cost reduction

It considerably reduces mass of the system

The positive work in isentropic expansion of liquid is very small

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

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

Condenser

Expansion valve

Compressor

Evaporator

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

None of these

Evaporator

Absorber

Condenser

Refrigeration & Air-Conditioning Practice Set-7

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