Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. 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

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

0.1 ton

10 tons

40 tons

5 tons

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

Sub-cooling or under-cooling

Super-cooling

Normal cooling

None of these

4. 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

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

More for small capacity and less for high capacity

Less

Same

6. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Centrifugal

Piston type reciprocating

7. 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)

8. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

9. 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

Positive

Negative

10. 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

1.33

4.33

3.33

2.33

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

10°C

5°C

20°C

15°C

12. 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

0.6

0.376

0.67

13. The freezing point of sulphur dioxide is

-77.7°C

-75.2°C

-56.6°C

-135.8°C

14. In a lithium bromide absorption refrigeration system

None of these

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

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

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

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

8 bar

30 bar

15 bar

2 bar

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

Compressor and condenser

Evaporator and compressor

Receiver and evaporator

Condenser and receiver

17. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

18. 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

Carbon dioxide

Brine

Ammonia

Freon

19. 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

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

Absorber

Condenser, absorber and separator (rectifier)

Evaporator

Condenser

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21. Freon group of refrigerants are

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

Inflammable

22. 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

23. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Four heat exchangers

Three heat exchangers

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

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

Wet bulb temperature of air

25. 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.

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

Always more than unity

Always less than unity

Any one of the above

Equal to unity

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

Takes place at constant pressure

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

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

Good electrical conductor

High risibility with oil

Low boiling point

Large latent heat

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

30. 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

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

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

Optimum

Any value

Low

High

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

Stirling

Bell Coleman

Carnot

Ericson

33. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

A gas will never liquefy

34. 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

35. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

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

Room air conditioners

Water coolers

Domestic refrigerators

All of these

37. The boiling point of ammonia is

-10.5°C

-77.7°C

-30°C

-33.3°C

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

Capillary tubes

Evaporator tubes

Condenser tubes

Refrigerant cooling tubes

39. 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

40. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

None of the above

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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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