Refrigeration & Air-Conditioning Practice Set-3

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1. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-56.6°C

-135.8°C

2. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Low boiling point

High risibility with oil

Good electrical conductor

3. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

4. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Inflammable

Non-inflammable and toxic

5. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dry bulb temperature

Dew point temperature

6. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Always less than unity

Any one of the above

7. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Carbon dioxide

Brine

8. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

9. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

5

0.2

1.2

6

10. The bank of tubes at the back of domestic refrigerator is

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

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11. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

12. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(C) Sum of (A) and (B)

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

13. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

More

14. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

15. Most thermostatic expansion valves are set for a superheat of

15°C

20°C

5°C

10°C

16. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

17. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

2 bar

15 bar

18. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

19. The boiling point of ammonia is

-30°C

-77.7°C

-10.5°C

-33.3°C

20. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

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21. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Positive

Zero

Negative

None of these

22. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Carnot

Ericson

23. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

24. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

None of these

Super-cooling

Normal cooling

25. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

26. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

27. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.6

0.376

28. Rating of a domestic refrigerator is of the order of

10 tons

40 tons

5 tons

0.1 ton

29. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

Domestic refrigerators

All of these

30. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

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31. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

9: 1

1: 9

1: 1

32. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1

1.25

2.15

33. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Axial

Centrifugal

34. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

35. For obtaining high COP, the pressure range of compressor should be

High

Optimum

Low

Any value

36. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

More

37. Which of the following statement is correct?

(D) Both (A) and (B)

(C) The warm air increases the rate of radiation of heat from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

38. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

39. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

2.33

1.33

4.33

40. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

Takes place at constant pressure

Refrigeration & Air-Conditioning Practice Set-3

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