Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. 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

Freon

Ammonia

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

Water coolers

Domestic refrigerators

All of these

Room air conditioners

3. Critical temperature is the temperature above which

Water will never evaporate

A gas will never liquefy

Water will evaporate

A gas will immediately liquefy

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

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

5. 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)

6. 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

7. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Piston type reciprocating

Centrifugal

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

Bell Coleman

Ericson

Carnot

Stirling

9. 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

2.33

1.33

3.33

4.33

10. In a lithium bromide absorption refrigeration system

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

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

None of these

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

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11. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-135.8°C

-75.2°C

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

Less

Same

More for small capacity and less for high capacity

13. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 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

14. 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: 3

1: 1

9: 1

15. Freon group of refrigerants are

Inflammable

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

16. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

17. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

18. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Above critical temperature

Near critical temperature of refrigerant

At critical Temperature

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

Any one of the above

Always more than unity

Always less than unity

Equal to unity

20. A bootstrap air cooling system has

Four heat exchangers

One heat exchanger

Two heat exchangers

Three heat exchangers

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21. 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

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

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

23. 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

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

10 tons

40 tons

5 tons

0.1 ton

25. 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

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

Takes place at constant entropy

Takes place at constant pressure

Takes place at constant temperature

Involves no change in volume

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

Superheated vapour

Wet vapour

Saturated liquid

Dry saturated vapour

28. 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.

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

Any value

Low

Optimum

High

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

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

Condenser and receiver

Page 4 of 4

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

Normal cooling

Sub-cooling or under-cooling

None of these

Super-cooling

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

10°C

20°C

5°C

15°C

33. 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)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

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

Good electrical conductor

Low boiling point

Large latent heat

High risibility with oil

35. 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

Positive

None of these

Zero

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

2 bar

15 bar

8 bar

30 bar

37. 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

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

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

Absorber

39. A thermostatic expansion valve in a refrigeration system

None of the above

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

40. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Dry bulb temperature

Wet bulb temperature

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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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