Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Sub-cooling or under-cooling

None of these

Normal cooling

Super-cooling

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

Same

Less

More for small capacity and less for high capacity

3. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

4. 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

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

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

Absorber

6. 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

0.4

0.67

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

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

8. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

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

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

9. Which of the following statement is correct?

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

(D) Both (A) and (B)

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

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

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

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11. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Bell Coleman

Carnot

Stirling

Ericson

13. 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 - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

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

0.1 ton

10 tons

5 tons

40 tons

15. 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

Brine

Carbon dioxide

Ammonia

Freon

16. 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

17. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

18. 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

19. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

20. 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

2.15

5.12

1.25

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21. The boiling point of ammonia is

-33.3°C

-10.5°C

-77.7°C

-30°C

22. In a lithium bromide absorption refrigeration system

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

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

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

All of these

Room air conditioners

Water coolers

Domestic refrigerators

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

25. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

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

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

27. 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

28. 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

29. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

30. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Carnot

Reversed Rankine

Rankine

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31. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-75.2°C

-77.7°C

32. 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: 3

1: 9

1: 1

33. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

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

2 bar

15 bar

8 bar

30 bar

35. 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

36. 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

Negative

Positive

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

Low

Optimum

High

Any value

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

15°C

20°C

5°C

10°C

39. 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

40. 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

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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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