Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

The positive work in isentropic expansion of liquid is very small

It considerably reduces mass of the system

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

It leads to significant cost reduction

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

Wet bulb temperature

Dry bulb temperature

Specific humidity

Dew point temperature

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

Carbon dioxide

Ammonia

R-12

Sulphur dioxide

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

Zero

Negative

None of these

Positive

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

Horizontal and uniformly spaced

Curved lines

Vertical and uniformly spaced

Horizontal and non-uniformly spaced

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

Evaporator

Compressor

Expansion valve

Condenser

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

Absorber

Condenser

Evaporator

None of these

8. During sensible cooling of air, specific humidity

Remains constant

Increases

None of these

Decreases

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

Horizontal line

Inclined line

Curved line

Vertical line

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

Rotating

Reciprocating

Screw

Centrifugal

Page 2 of 4

11. 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

None of the above

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

12. The specific humidity during humidification process

Remains constant

Decreases

Increases

None of these

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

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Specific humidity

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

High

Very low

Same

Low

15. A refrigerant compressor is used to

Raise the pressure of the refrigerant

Circulate the refrigerant through the refrigerating system

All of the above

Raise the temperature of the refrigerant

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

R-12

Ammonia

Carbon dioxide

Sulphur dioxide

17. 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

18. 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

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

Lower than

None of these

Higher than

Same as

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

Isentropic compression process

Constant pressure expansion process

Constant pressure cooling process

Isentropic expansion process

Page 3 of 4

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

Same

Lower

Higher

None of these

22. Air refrigerator works on

(b) Bell Coleman cycle

None of these

(a) Reversed Carnot cycle

Both (A) and (B)

23. 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.

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

Before expansion valve

Between condenser and evaporator

In evaporator

Between compressor and condenser

25. The relative coefficient of performance is equal to

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

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

None of these

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

26. 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

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

5°C

14°C

8°C

22°C

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

Dehumidification

Cooling and dehumidification

Heating and humidification

Humidification

29. The wet bulb temperature during sensible cooling of air

Increases

None of these

Remains constant

Decreases

30. Moisture should be removed from refrigerants to avoid

All of these

Freezing at the expansion valve

Corrosion of steel plates

Restriction to refrigerant flow

Page 4 of 4

31. 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

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

All of these

Sulphur sticks

Soap and water

Halide torch

33. 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

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

Condensation

Expansion

Compression

Evaporation

35. A refrigerant with the highest critical pressure is

Ammonia

R-12

R-22

R-11

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

Wet bulb depression

Dew point depression

Degree of saturation

Dry bulb depression

37. 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

Condenser

Compressor

Expansion valve

38. The undesirable property of a refrigerant is

Non-flammable

High boiling point

Non-explosive

Non-toxic

Refrigeration & Air-Conditioning Practice Set-7

Related

Leave a ReplyCancel reply

Secured Payments

Protection

Refrigeration & Air-Conditioning Practice Set-7

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Secured Payments

Protection