Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

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

1.33

2.33

3.33

4.33

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

Always more than unity

Always less than unity

Equal to unity

Any one of the above

4. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

5. Critical temperature is the temperature above which

Water will evaporate

Water will never evaporate

A gas will never liquefy

A gas will immediately liquefy

6. Which of the following statement is correct?

(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.

(D) Both (A) and (B)

7. 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

8. 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

1.2

0.2

9. 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 temperature

Involves no change in volume

Takes place at constant pressure

10. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

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11. 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

Negative

Zero

Positive

12. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-56.6°C

-77.7°C

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

Carnot

Stirling

Bell Coleman

Ericson

14. 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: 9

1: 1

15. 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

16. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

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

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

18. 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

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

None of these

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

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

20. 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

0.6

0.67

0.4

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

15 bar

30 bar

8 bar

2 bar

22. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

Above critical temperature

23. 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

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

(B) Heat stored in the human body

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

Room air conditioners

All of these

Domestic refrigerators

Water coolers

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

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

Condenser tubes

26. 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

1 to 2 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

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

High risibility with oil

Large latent heat

Good electrical conductor

Low boiling point

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

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

Condenser

29. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Nontoxic and non-inflammable

Inflammable

30. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

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31. 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

Unpredictable

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

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

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

5 tons

0.1 ton

10 tons

40 tons

34. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

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

More for small capacity and less for high capacity

Less

Same

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

Optimum

Any value

High

Low

37. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Two heat exchangers

Four heat exchangers

38. 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

Ammonia

Brine

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

Sub-cooling or under-cooling

Super-cooling

Normal cooling

None of these

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

20°C

5°C

15°C

10°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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