Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Two heat exchangers

Three heat exchangers

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

1: 1

9: 1

1: 3

1: 9

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

Superheated vapour

Dry saturated vapour

Wet vapour

Saturated liquid

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

Condenser

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

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/ (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

6. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Toxic

Inflammable

7. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

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

40 tons

5 tons

10 tons

0.1 ton

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

Super-cooling

None of these

Normal cooling

Sub-cooling or under-cooling

10. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

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11. 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)

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

12. 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)

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

13. 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

1.33

4.33

2.33

14. A thermostatic expansion valve in a refrigeration system

None of the above

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

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

5°C

20°C

10°C

15°C

16. 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

Freon

Carbon dioxide

Ammonia

17. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-75.2°C

-135.8°C

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

Same

Less

More for small capacity and less for high capacity

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

Ericson

Bell Coleman

Stirling

Carnot

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

Equally

Unpredictable

Less

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21. 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

5.12

2.15

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

Domestic refrigerators

Water coolers

Room air conditioners

All of these

23. 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

24. The boiling point of ammonia is

-77.7°C

-10.5°C

-33.3°C

-30°C

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

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

26. 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 temperature

Takes place at constant pressure

27. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Miniature sealed unit

Centrifugal

Axial

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

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Collect vapours

Detect liquid in vapour

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

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

30. 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

Negative

Zero

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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

0.6

0.67

0.4

0.376

32. 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

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

2 bar

30 bar

15 bar

8 bar

34. In a lithium bromide absorption refrigeration system

None of these

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

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

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

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

High

Optimum

Low

Any value

36. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Wet bulb temperature

Dry bulb temperature

37. 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

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

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

39. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

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

Large latent heat

Low boiling point

Good electrical conductor

High risibility with oil

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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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