Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

2. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-56.6°C

-75.2°C

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

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

4. In a lithium bromide absorption refrigeration system

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

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

5. 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

0.5 to 0.8 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

6. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

7. 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

0.4

0.376

0.67

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

Any one of the above

Equal to unity

Always more than unity

Always less than unity

9. 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

10. 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.

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11. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

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

10 tons

0.1 ton

5 tons

40 tons

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

Ammonia

Brine

Carbon dioxide

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

5°C

10°C

15°C

20°C

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

30 bar

8 bar

2 bar

15 bar

16. 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

17. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Reversed Carnot

Carnot

18. 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: 3

1: 1

19. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

20. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

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

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

Detect liquid in vapour

22. 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

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

More for small capacity and less for high capacity

Same

Less

24. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Wet bulb temperature

Dry bulb temperature

25. 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

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

Capillary tubes

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

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

Ericson

Bell Coleman

Stirling

Carnot

28. 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

Is suitable only for constant load systems

None of the above

29. 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

30. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

At critical Temperature

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

Water coolers

All of these

Domestic refrigerators

Room air conditioners

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

Super-cooling

None of these

Normal cooling

Sub-cooling or under-cooling

33. 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

34. 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

1.25

2.15

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

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

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)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

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

Any value

Low

High

Optimum

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

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

39. The domestic refrigerator uses following type of compressor

Axial

Centrifugal

Miniature sealed unit

Piston type reciprocating

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

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

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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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