Refrigeration & Air-Conditioning Practice Set-3

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

5 tons

40 tons

0.1 ton

10 tons

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

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

3. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

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

Equally

More

Unpredictable

Less

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

9: 1

1: 3

1: 9

1: 1

6. In a lithium bromide absorption refrigeration system

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

None of these

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

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

7. 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

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

8. 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

Carbon dioxide

Freon

Brine

9. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

10. 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

2.15

1.25

5.12

1

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

None of these

Normal cooling

Sub-cooling or under-cooling

Super-cooling

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

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

13. 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)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

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

(A) Heat dissipated to the surroundings

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

(B) Heat stored in the human body

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

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

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

Condenser

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

5°C

10°C

15°C

20°C

17. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Rankine

Reversed Carnot

Carnot

18. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

19. The boiling point of ammonia is

-30°C

-33.3°C

-77.7°C

-10.5°C

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

Ericson

Bell Coleman

Stirling

Carnot

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21. 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

0.2

6

1.2

5

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

More for small capacity and less for high capacity

More

Less

Same

23. Which of the following statement is correct?

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

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

(D) Both (A) and (B)

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

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

2 bar

8 bar

30 bar

15 bar

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

High

Any value

Low

Optimum

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

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

28. 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

2.33

1.33

3.33

4.33

29. 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

0.376

0.6

0.67

0.4

30. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

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

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

32. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

33. 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

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

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

35. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

Toxic

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

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

37. 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

None of these

Zero

Negative

Positive

38. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

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

Domestic refrigerators

Water coolers

All of these

Room air conditioners

40. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

Refrigeration & Air-Conditioning Practice Set-3

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