Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. 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

Positive

None of these

Zero

Negative

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

High risibility with oil

Low boiling point

Good electrical conductor

Large latent heat

3. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

5. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

6. 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.

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

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

8. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Rankine

Carnot

Reversed Carnot

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

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

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

10. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

Four heat exchangers

One heat exchanger

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11. 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

12. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

13. 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 temperature

Takes place at constant pressure

14. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Toxic

Non-inflammable and toxic

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

Any value

High

Low

Optimum

16. 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

0.1 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

17. 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

18. 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

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

Receiver and evaporator

Condenser and receiver

Evaporator and compressor

Compressor and condenser

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

1.25

5.12

2.15

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21. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

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

Condenser, absorber and separator (rectifier)

Condenser

Evaporator

Absorber

23. 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

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

8 bar

15 bar

2 bar

30 bar

25. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

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

None of these

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

26. The domestic refrigerator uses following type of compressor

Piston type reciprocating

Centrifugal

Axial

Miniature sealed unit

27. The freezing point of sulphur dioxide is

-135.8°C

-56.6°C

-77.7°C

-75.2°C

28. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

29. 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

1: 1

9: 1

1: 3

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

More for small capacity and less for high capacity

Less

Same

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31. 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/ (T₂ - T₁)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

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

Ericson

Bell Coleman

Carnot

Stirling

33. 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

0.4

0.376

0.6

0.67

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

10 tons

5 tons

0.1 ton

40 tons

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

5°C

20°C

10°C

15°C

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

Always less than unity

Equal to unity

Any one of the above

Always more than unity

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

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

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

Ambient air temperature

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

39. 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

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

Room air conditioners

All of these

Water coolers

Domestic refrigerators

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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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