Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. 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)

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

Stirling

Bell Coleman

Carnot

Ericson

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

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

4. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

5. In a lithium bromide absorption refrigeration system

None of these

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

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

3.33

2.33

1.33

7. The boiling point of ammonia is

-30°C

-10.5°C

-33.3°C

-77.7°C

8. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

None of the above

9. 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

10. 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

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

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

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

12. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

13. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

15. Freon group of refrigerants are

Inflammable

Non-inflammable and toxic

Toxic

Nontoxic and non-inflammable

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

Receiver and evaporator

Condenser and receiver

Compressor and condenser

Evaporator and compressor

17. 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

Positive

None of these

Negative

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

Absorber

Condenser

Condenser, absorber and separator (rectifier)

Evaporator

19. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

A gas will never liquefy

Water will evaporate

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

5 tons

40 tons

0.1 ton

10 tons

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21. 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

Ammonia

Brine

Carbon dioxide

Freon

22. 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: 1

1: 3

1: 9

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

Good electrical conductor

High risibility with oil

Large latent heat

Low boiling point

24. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Wet bulb temperature

Relative humidity

Dew point temperature

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

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

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

Room air conditioners

Domestic refrigerators

Water coolers

All of these

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

8 bar

15 bar

2 bar

30 bar

28. 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

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

Any value

Low

High

Optimum

30. The freezing point of sulphur dioxide is

-77.7°C

-75.2°C

-56.6°C

-135.8°C

Page 4 of 4

31. 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

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

Same

More for small capacity and less for high capacity

Less

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

Takes place at constant pressure

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

34. Which of the following statement is correct?

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

(D) Both (A) and (B)

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

35. 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

36. 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

0.376

0.4

0.6

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

20°C

5°C

15°C

10°C

38. 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

39. 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

Superheat the vapour

Collect vapours

40. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

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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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