Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

2. 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

2.33

1.33

3.33

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

Large latent heat

Good electrical conductor

Low boiling point

High risibility with oil

4. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

At critical Temperature

5. 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)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

6. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

Four heat exchangers

One heat exchanger

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

Equal to unity

Always more than unity

Any one of the above

Always less than unity

8. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

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

0.2

1.2

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

All of these

Domestic refrigerators

Room air conditioners

Water coolers

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11. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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

Same

More for small capacity and less for high capacity

Less

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

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

15. 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

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

15°C

20°C

10°C

5°C

17. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

18. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-77.7°C

-56.6°C

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

Compressor and condenser

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

20. 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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21. Which of the following statement is correct?

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

22. 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

23. 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

0.6

0.4

0.376

24. 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: 1

1: 9

25. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Axial

Piston type reciprocating

26. 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

27. 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

Brine

Freon

Ammonia

28. In a lithium bromide absorption refrigeration system

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

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

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

Evaporator

Condenser

Absorber

Condenser, absorber and separator (rectifier)

30. 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

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31. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

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

15 bar

2 bar

8 bar

30 bar

33. 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

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

(B) Heat stored in the human body

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

(A) Heat dissipated to the surroundings

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

Optimum

High

Low

Any value

36. Freon group of refrigerants are

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

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

Bell Coleman

Carnot

Stirling

Ericson

38. 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

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

5 tons

10 tons

40 tons

0.1 ton

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

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

Evaporator tubes

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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