Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

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

Refrigerant cooling tubes

Capillary tubes

Evaporator tubes

Condenser tubes

3. 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

Super-cooling

None of these

4. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

5. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

One heat exchanger

Three heat exchangers

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

15 bar

2 bar

30 bar

8 bar

7. 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

8. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Above critical temperature

Much below critical temperature

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

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

10. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

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11. 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

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

Wet vapour

Dry saturated vapour

Saturated liquid

Superheated vapour

13. 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

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

Carnot

Bell Coleman

Stirling

Ericson

15. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

16. 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

0.4

0.376

0.6

17. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

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

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

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

Evaporator

Condenser

Absorber

Condenser, absorber and separator (rectifier)

20. 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)

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21. 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

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

22. In a lithium bromide absorption refrigeration system

Water 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

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

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

20°C

15°C

10°C

5°C

24. 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

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

Same

Less

More for small capacity and less for high capacity

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 temperature

Takes place at constant pressure

Involves no change in volume

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

Always less than unity

Any one of the above

Always more than unity

Equal to unity

28. 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

3.33

1.33

2.33

4.33

29. The boiling point of ammonia is

-10.5°C

-33.3°C

-30°C

-77.7°C

30. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-77.7°C

-56.6°C

Page 4 of 4

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

Domestic refrigerators

Water coolers

Room air conditioners

All of these

32. 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

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

0.1 ton

10 tons

40 tons

5 tons

34. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

35. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Carnot

Rankine

Reversed Carnot

36. 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: 9

1: 3

1: 1

37. 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

38. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

39. 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.

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

Optimum

Any value

Low

High

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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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