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

Super-cooling

None of these

Sub-cooling or under-cooling

Normal cooling

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

10 tons

5 tons

40 tons

0.1 ton

3. 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

2.33

1.33

3.33

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

High risibility with oil

Good electrical conductor

Large latent heat

Low boiling point

5. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following 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

2 to 5 h.p. per ton of refrigeration

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

0.67

0.6

0.4

0.376

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

Always less than unity

Any one of the above

Equal to unity

Always more than unity

8. 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

None of these

Positive

Zero

9. 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

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

8 bar

30 bar

15 bar

2 bar

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

Ericson

Stirling

Bell Coleman

Carnot

12. 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

13. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Relative humidity

Wet bulb temperature

14. 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

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

Evaporator and compressor

Compressor and condenser

Condenser and receiver

Receiver and evaporator

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

Less

More for small capacity and less for high capacity

Same

18. A bootstrap air cooling system has

Two heat exchangers

One heat exchanger

Four heat exchangers

Three heat exchangers

19. 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

20. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

Water will never evaporate

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21. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

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

Room air conditioners

Water coolers

Domestic refrigerators

All of these

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

Condenser tubes

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

24. 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.

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

5°C

15°C

10°C

20°C

26. 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

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

27. The boiling point of ammonia is

-30°C

-10.5°C

-33.3°C

-77.7°C

28. 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

29. 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

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

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Superheat the vapour

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31. 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)

32. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

33. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

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

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

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

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

36. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Axial

Centrifugal

37. 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

38. 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

9: 1

1: 3

1: 9

39. 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

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

Optimum

Any value

High

Low

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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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