Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

2. 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)

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

4. 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

Zero

None of these

Positive

Negative

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. 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

3.33

1.33

7. 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)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

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

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Collect vapours

Superheat the vapour

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

Low boiling point

Good electrical conductor

Large latent heat

High risibility with oil

10. 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 temperature

Takes place at constant pressure

Takes place at constant entropy

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11. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

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

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

13. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Reversed Carnot

Rankine

Carnot

14. 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

0.67

0.4

0.6

15. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

16. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

17. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-77.7°C

-75.2°C

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

40 tons

0.1 ton

5 tons

10 tons

19. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Toxic

Nontoxic and non-inflammable

20. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

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21. 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

22. 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

23. 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

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

Low

Optimum

High

Any value

25. 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

2.15

1.25

26. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Four heat exchangers

Three heat exchangers

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

Water coolers

Domestic refrigerators

Room air conditioners

All of these

28. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following 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

0.5 to 0.8 h.p. per ton of refrigeration

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

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

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

30 bar

15 bar

8 bar

2 bar

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31. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

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

32. In a lithium bromide absorption refrigeration system

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

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

None of these

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

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

Less

Same

More for small capacity and less for high capacity

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

Equal to unity

Always more than unity

Always less than unity

Any one of the above

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

Carnot

Ericson

Stirling

Bell Coleman

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

20°C

10°C

5°C

15°C

37. The boiling point of ammonia is

-30°C

-77.7°C

-33.3°C

-10.5°C

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

Condenser, absorber and separator (rectifier)

Condenser

Evaporator

Absorber

39. 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

Freon

Carbon dioxide

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

Evaporator tubes

Capillary tubes

Condenser tubes

Refrigerant cooling 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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