Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Same

Less

More for small capacity and less for high capacity

2. 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

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

Domestic refrigerators

Water coolers

Room air conditioners

All of these

4. 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)

5. The boiling point of ammonia is

-10.5°C

-77.7°C

-30°C

-33.3°C

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

40 tons

5 tons

0.1 ton

10 tons

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

Large latent heat

Good electrical conductor

Low boiling point

High risibility with oil

8. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

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

Superheat the vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

10. 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

0.376

0.4

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11. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Carnot

Reversed Carnot

12. 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)

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

15°C

10°C

20°C

5°C

14. 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

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

Bell Coleman

Stirling

Ericson

Carnot

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

Freon

Brine

Carbon dioxide

Ammonia

17. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

None of the above

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

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

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

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

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

Absorber

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

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

Compressor and condenser

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21. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

One heat exchanger

Four heat exchangers

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

23. 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

24. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

25. 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

26. 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

Positive

Zero

Negative

27. 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

3.33

1.33

2.33

28. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

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

Optimum

High

Any value

Low

30. In a lithium bromide absorption refrigeration system

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

Ammonia 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

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31. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

Takes place at constant pressure

32. 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

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

(A) Heat dissipated to the surroundings

33. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

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

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

Evaporator tubes

35. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-56.6°C

-77.7°C

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

Always more than unity

Equal to unity

Always less than unity

Any one of the above

37. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

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

Normal cooling

Super-cooling

None of these

Sub-cooling or under-cooling

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

15 bar

8 bar

30 bar

2 bar

40. 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

1: 9

1: 3

9: 1

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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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