Refrigeration & Air-Conditioning Practice Set-7

Page 1 of 4

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

2. 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

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

Wet bulb depression

Degree of saturation

Dew point depression

Dry bulb depression

4. The relative coefficient of performance is equal to

None of these

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

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

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

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

Specific humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

6. 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

4

1/3

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

Before entering the compressor

Before entering the condenser

After leaving the compressor

After leaving the condenser

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

Zero

Positive

None of these

Negative

9. The wet bulb temperature during sensible cooling of air

Decreases

None of these

Remains constant

Increases

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

Expansion

Compression

Condensation

Evaporation

Page 2 of 4

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

Condenser

Expansion valve

Evaporator

Compressor

12. 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 humidified

Heated and dehumidified

Cooled and humidified

Cooled and dehumidified

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

1 - B.P.F.

1/ B.P.F.

1 + B.P.F.

B.P.F. - 1

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

All of these

Soap and water

Halide torch

Sulphur sticks

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

Wet bulb temperature

Dry bulb temperature

Specific humidity

Dew point temperature

16. Air refrigerator works on

Both (A) and (B)

None of these

(b) Bell Coleman cycle

(a) Reversed Carnot cycle

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

Isentropic compression process

Isentropic expansion process

Constant pressure cooling process

Constant pressure expansion process

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

Vertical line

Curved line

Horizontal line

Inclined line

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

None of the above

20. 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

Page 3 of 4

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

Reciprocating

Rotating

Screw

Centrifugal

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

Lower

None of these

Higher

Same

23. 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

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

Same as

Lower than

None of these

Higher than

25. The undesirable property of a refrigerant is

Non-toxic

High boiling point

Non-flammable

Non-explosive

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

Condenser to the evaporator

Evaporator to the thermostat

Expansion valve to the evaporator

Condenser to the expansion valve

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

1 + C.O.P

1 + (1/C.O.P)

1 - (1/C.O.P)

1 - C.O.P.

28. A refrigerant with the highest critical pressure is

R-22

Ammonia

R-11

R-12

29. Moisture should be removed from refrigerants to avoid

Freezing at the expansion valve

Corrosion of steel plates

Restriction to refrigerant flow

All of these

30. A refrigerant compressor is used to

Raise the temperature of the refrigerant

Circulate the refrigerant through the refrigerating system

Raise the pressure of the refrigerant

All of the above

Page 4 of 4

31. During sensible cooling of air, specific humidity

Decreases

None of these

Remains constant

Increases

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

Cooling and dehumidification

Heating and humidification

Humidification

Dehumidification

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

8°C

22°C

5°C

14°C

34. The specific humidity during humidification process

None of these

Increases

Decreases

Remains constant

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

Carbon dioxide

Ammonia

Sulphur dioxide

R-12

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

Between compressor and condenser

Between condenser and evaporator

In evaporator

Before expansion valve

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

High

Low

Same

Very low

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

Evaporator

None of these

Condenser

Absorber

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