Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

Dry bulb temperature of air

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

Large latent heat

Good electrical conductor

Low boiling point

High risibility with oil

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

Evaporator

Absorber

Condenser

Condenser, absorber and separator (rectifier)

4. 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

5. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

One heat exchanger

Two heat exchangers

6. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

Inflammable

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 - T₁)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

8. 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

9: 1

1: 1

9. In a lithium bromide absorption refrigeration system

None of these

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

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

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

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

Stirling

Bell Coleman

Ericson

Carnot

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11. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Above critical temperature

Near critical temperature of refrigerant

At critical Temperature

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

Equal to unity

Always less than unity

Always more than unity

Any one of the above

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

High

Low

Optimum

Any value

14. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

15. 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

Ammonia

Freon

Carbon dioxide

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

Refrigerant cooling tubes

Evaporator tubes

Capillary tubes

Condenser tubes

17. 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

0.6

0.4

0.67

0.376

18. The domestic refrigerator uses following type of compressor

Centrifugal

Miniature sealed unit

Piston type reciprocating

Axial

19. 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

None of the above

Maintains different temperatures in evaporator in proportion to load

20. 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

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

(A) Heat dissipated to the surroundings

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21. 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

22. 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

None of these

Positive

Negative

Zero

23. The boiling point of ammonia is

-10.5°C

-33.3°C

-77.7°C

-30°C

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

Less

Same

More for small capacity and less for high capacity

25. 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

2.33

4.33

1.33

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

0.1 ton

40 tons

5 tons

10 tons

27. 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

2 to 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

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

Domestic refrigerators

All of these

Room air conditioners

Water coolers

29. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

30. 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

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31. 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.

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

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

33. The freezing point of sulphur dioxide is

-77.7°C

-56.6°C

-75.2°C

-135.8°C

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

Less

Unpredictable

Equally

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

5°C

10°C

15°C

20°C

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

15 bar

2 bar

30 bar

8 bar

37. 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

38. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

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

Collect vapours

Superheat the vapour

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

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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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