Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

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

Sub-cooling or under-cooling

Normal cooling

None of these

Super-cooling

2. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Wet bulb temperature

Dry bulb temperature

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

Absorber

Condenser

Evaporator

Condenser, absorber and separator (rectifier)

4. 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

Freon

Carbon dioxide

Ammonia

Brine

5. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

6. Freon group of refrigerants are

Inflammable

Toxic

Nontoxic and non-inflammable

Non-inflammable and toxic

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

Bell Coleman

Ericson

Stirling

Carnot

8. 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

9. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

10. 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

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

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

12. 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

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

13. 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.

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

Equal to unity

Always more than unity

Always less than unity

Any one of the above

15. 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: 1

1: 3

1: 9

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

Condenser tubes

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

17. 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

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

8 bar

15 bar

30 bar

2 bar

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

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

20. In a lithium bromide absorption refrigeration system

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

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

None of these

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

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

Domestic refrigerators

Water coolers

All of these

Room air conditioners

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

Low

Any value

Optimum

High

23. 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

0.376

0.4

0.6

0.67

24. 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

4.33

1.33

3.33

2.33

25. 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)

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

5 tons

0.1 ton

40 tons

10 tons

27. 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

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

(B) Heat stored in the human body

28. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

None of the above

Ensures the evaporator completely filled with refrigerant of the load

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

15°C

5°C

20°C

10°C

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

High risibility with oil

Good electrical conductor

Low boiling point

Large latent heat

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31. 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

5.12

1.25

2.15

32. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Centrifugal

Miniature sealed unit

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

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

34. The boiling point of ammonia is

-30°C

-33.3°C

-77.7°C

-10.5°C

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

Wet vapour

Saturated liquid

Dry saturated vapour

Superheated vapour

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

Involves no change in volume

Takes place at constant pressure

Takes place at constant entropy

Takes place at constant temperature

38. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

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

More for small capacity and less for high capacity

Less

Same

40. The vapour compression refrigerator employs the following cycle

Reversed Rankine

Carnot

Rankine

Reversed Carnot

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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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