Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Stirling

Ericson

Carnot

Bell Coleman

2. 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

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

3. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

4. In a lithium bromide absorption refrigeration system

None of these

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

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

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

5. 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

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

Less

Same

More for small capacity and less for high capacity

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

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

Dew point temperature of air

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

Large latent heat

Good electrical conductor

High risibility with oil

Low boiling point

9. Which of the following statement is correct?

(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.

(D) Both (A) and (B)

10. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Axial

Miniature sealed unit

Centrifugal

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11. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Reversed Rankine

Carnot

12. 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

13. 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

Freon

Brine

Carbon dioxide

Ammonia

14. 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

(A) Heat dissipated to the surroundings

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

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

High

Low

Optimum

Any value

16. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dew point temperature

Relative humidity

Dry bulb temperature

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

Super-cooling

Normal cooling

None of these

Sub-cooling or under-cooling

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

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

19. A bootstrap air cooling system has

Three heat exchangers

Four heat exchangers

Two heat exchangers

One heat exchanger

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

Room air conditioners

All of these

Water coolers

Domestic refrigerators

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

10°C

20°C

15°C

5°C

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

Less

Equally

Unpredictable

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

Dry saturated vapour

Saturated liquid

Wet vapour

Superheated vapour

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

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

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

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

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

30 bar

8 bar

15 bar

2 bar

27. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

Much below critical temperature

At critical Temperature

28. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

29. The freezing point of sulphur dioxide is

-56.6°C

-77.7°C

-135.8°C

-75.2°C

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

0.1 ton

40 tons

5 tons

10 tons

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31. 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

2.15

5.12

32. 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

33. 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

34. 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

35. Freon group of refrigerants are

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

Toxic

36. 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)

37. 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 entropy

Takes place at constant temperature

Takes place at constant pressure

38. 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

4.33

2.33

3.33

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

1: 9

9: 1

1: 1

1: 3

40. The boiling point of ammonia is

-33.3°C

-10.5°C

-30°C

-77.7°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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