Refrigeration & Air-Conditioning Practice Set-3

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

Ericson

Carnot

Stirling

Bell Coleman

2. 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

5

1.2

6

3. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

4. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

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: 9

1: 3

1: 1

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

Positive

None of these

Zero

Negative

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

Compressor and condenser

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

8. A bootstrap air cooling system has

Four heat exchangers

Two heat exchangers

One heat exchanger

Three heat exchangers

9. 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

10. 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

Brine

Ammonia

Carbon dioxide

Freon

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

Good electrical conductor

Large latent heat

High risibility with oil

Low boiling point

12. 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

13. 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)

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

(B) Heat stored in the human body

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

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

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

Room air conditioners

Domestic refrigerators

All of these

Water coolers

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

5°C

15°C

10°C

20°C

17. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Carnot

Reversed Rankine

Rankine

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

Wet vapour

Superheated vapour

Dry saturated vapour

Saturated liquid

19. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

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

2.15

5.12

1.25

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21. Which of the following statement is correct?

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

(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.

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

Any value

Optimum

High

Low

23. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-77.7°C

-56.6°C

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

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

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

30 bar

8 bar

2 bar

15 bar

26. 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

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

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

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

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

Less

More for small capacity and less for high capacity

Same

More

29. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Above critical temperature

Much below critical temperature

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

More

Less

Equally

Unpredictable

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31. 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

32. The boiling point of ammonia is

-30°C

-77.7°C

-10.5°C

-33.3°C

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

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

Superheat the vapour

34. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

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

Always more than unity

Equal to unity

Always less than unity

Any one of the above

36. 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

4.33

3.33

1.33

2.33

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

40 tons

10 tons

0.1 ton

5 tons

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)

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

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

Condenser

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

40. In a lithium bromide absorption refrigeration system

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

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

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

None of these

Refrigeration & Air-Conditioning Practice Set-3

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