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

Good electrical conductor

High risibility with oil

Large latent heat

2. 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

Ammonia

Freon

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

Same

Less

More for small capacity and less for high capacity

4. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Carnot

Rankine

Reversed Rankine

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

Optimum

Any value

High

Low

6. 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

1.25

5.12

7. 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

8. The boiling point of ammonia is

-77.7°C

-10.5°C

-30°C

-33.3°C

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

15 bar

30 bar

8 bar

2 bar

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

15°C

5°C

10°C

20°C

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11. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dew point temperature

Dry bulb temperature

Relative humidity

12. Freon group of refrigerants are

Non-inflammable and toxic

Toxic

Inflammable

Nontoxic and non-inflammable

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

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

Evaporator tubes

14. 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.

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

Condenser and receiver

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

16. 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

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

None of these

17. The freezing point of sulphur dioxide is

-77.7°C

-135.8°C

-75.2°C

-56.6°C

18. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

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

Superheat the vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

20. 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

Page 3 of 4

21. 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

22. 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

23. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following 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

1 to 2 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

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

10 tons

5 tons

0.1 ton

40 tons

25. 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

26. 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

Negative

Positive

None of these

27. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

28. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

None of the above

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

Ericson

Stirling

Bell Coleman

Carnot

30. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

Four heat exchangers

One heat exchanger

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31. 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

32. 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

4.33

2.33

1.33

33. 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

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

Dew point temperature of air

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

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

Domestic refrigerators

Water coolers

All of these

Room air conditioners

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

Always less than unity

Equal to unity

Always more than unity

Any one of the above

37. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

Water will evaporate

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

Unpredictable

Equally

Less

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

Absorber

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

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

Dry saturated vapour

Wet vapour

Superheated vapour

Saturated liquid

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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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