Refrigeration & Air-Conditioning Practice Set-3

Page 1 of 4

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

Optimum

Any value

High

Low

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

1.2

6

5

3. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

4. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Carnot

Reversed Rankine

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

All of these

Room air conditioners

Water coolers

Domestic refrigerators

6. 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

5.12

1.25

1

7. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

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

Bell Coleman

Carnot

Stirling

Ericson

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

15°C

10°C

5°C

20°C

10. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Miniature sealed unit

Piston type reciprocating

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

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

Involves no change in volume

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

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

Low boiling point

High risibility with oil

Good electrical conductor

Large latent heat

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

5 tons

10 tons

40 tons

0.1 ton

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

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

16. 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

0.67

0.376

0.4

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

Always less than unity

Always more than unity

Equal to unity

Any one of the above

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

2 to 5 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

1 to 2 h.p. per ton of refrigeration

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

Capillary tubes

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

20. 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)

(B) Heat stored in the human body

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

(A) Heat dissipated to the surroundings

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21. 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

1.33

3.33

2.33

4.33

22. 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 - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

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

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Detect liquid in vapour

24. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Two heat exchangers

Four heat exchangers

25. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

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

More for small capacity and less for high capacity

More

Less

Same

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

Equally

Less

More

Unpredictable

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

Condenser

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

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

15 bar

30 bar

8 bar

2 bar

30. 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

Ammonia

Freon

Brine

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31. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

32. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

33. The boiling point of ammonia is

-30°C

-33.3°C

-77.7°C

-10.5°C

34. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

35. 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.

(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.

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

Normal cooling

None of these

Sub-cooling or under-cooling

Super-cooling

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

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

38. In a lithium bromide absorption refrigeration system

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

None of these

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

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

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

1: 9

1: 1

1: 3

9: 1

40. 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

Zero

None of these

Positive

Refrigeration & Air-Conditioning Practice Set-3

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