Refrigeration & Air-Conditioning Practice Set-3

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

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

2. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Axial

Centrifugal

3. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

4. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-56.6°C

-75.2°C

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

Receiver and evaporator

Compressor and condenser

Evaporator and compressor

Condenser and receiver

6. 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

Negative

Positive

Zero

None of these

7. In a lithium bromide absorption refrigeration system

None of these

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

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

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

8. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

9. 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

Carbon dioxide

Freon

Brine

Ammonia

10. 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

1: 9

1: 1

9: 1

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

Room air conditioners

Domestic refrigerators

All of these

Water coolers

12. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

13. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

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

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

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

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

Always less than unity

Any one of the above

Always more than unity

Equal to unity

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

Evaporator

Condenser

Absorber

Condenser, absorber and separator (rectifier)

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

5 tons

40 tons

0.1 ton

10 tons

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

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

19. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Two heat exchangers

Three heat exchangers

20. 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

1.25

1

2.15

5.12

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21. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

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

Same

More

Less

More for small capacity and less for high capacity

23. 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

24. 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

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

More

Equally

Unpredictable

Less

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

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

Condenser tubes

27. 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

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

15°C

20°C

10°C

5°C

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

Carnot

Ericson

Bell Coleman

Stirling

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

High risibility with oil

Low boiling point

Large latent heat

Good electrical conductor

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31. 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

32. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Carnot

Reversed Rankine

33. 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

0.6

0.4

0.376

0.67

34. Which of the following statement is correct?

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

(D) Both (A) and (B)

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

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

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

0.5 to 0.8 h.p. per ton of refrigeration

1 to 2 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

36. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

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

Low

High

Any value

Optimum

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

8 bar

30 bar

2 bar

15 bar

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

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

Refrigeration & Air-Conditioning Practice Set-3

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