Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. 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

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

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

Good electrical conductor

High risibility with oil

Low boiling point

Large latent heat

3. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Two heat exchangers

Three heat exchangers

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

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

5. 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

5.12

1.25

2.15

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

5 tons

10 tons

0.1 ton

40 tons

7. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Carnot

Reversed Carnot

Rankine

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

Same

Less

More for small capacity and less for high capacity

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. Most thermostatic expansion valves are set for a superheat of

20°C

5°C

15°C

10°C

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

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

12. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

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

(B) Heat stored in the human body

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

14. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

15. Critical temperature is the temperature above which

A gas will never liquefy

Water will evaporate

Water will never evaporate

A gas will immediately liquefy

16. In a lithium bromide absorption refrigeration system

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

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

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

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

18. 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

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

30 bar

2 bar

8 bar

15 bar

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

Equal to unity

Any one of the above

Always more than unity

Always less than unity

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21. Which of the following statement is correct?

(D) Both (A) and (B)

(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.

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

23. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

24. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Inflammable

Non-inflammable and toxic

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

Absorber

Condenser

Condenser, absorber and separator (rectifier)

Evaporator

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

Optimum

Low

Any value

High

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

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

28. 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

29. 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

4.33

1.33

30. 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

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31. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-56.6°C

-135.8°C

32. 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

Positive

None of these

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

All of these

Domestic refrigerators

Water coolers

Room air conditioners

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

Unpredictable

Equally

Less

35. 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 pressure

Involves no change in volume

Takes place at constant temperature

36. 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

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

Bell Coleman

Carnot

Ericson

Stirling

38. 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

0.67

0.376

39. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Piston type reciprocating

Miniature sealed unit

40. The boiling point of ammonia is

-10.5°C

-77.7°C

-33.3°C

-30°C

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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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