Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

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

10 tons

5 tons

0.1 ton

40 tons

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

Wet vapour

Saturated liquid

Superheated vapour

Dry saturated vapour

3. 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

0.6

0.4

0.376

4. 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

5. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

6. 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.

7. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 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

8. 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

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

Any value

High

Optimum

Low

10. 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

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

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

12. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

One heat exchanger

Four heat exchangers

13. The freezing point of sulphur dioxide is

-75.2°C

-56.6°C

-135.8°C

-77.7°C

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

10°C

5°C

15°C

20°C

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

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

Capillary tubes

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

None of these

Super-cooling

Normal cooling

Sub-cooling or under-cooling

17. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 9

1: 3

9: 1

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

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

Compressor and condenser

19. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

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

More for small capacity and less for high capacity

Same

Less

Page 3 of 4

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

Dry bulb temperature of air

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

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

Negative

Zero

None of these

Positive

23. 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

24. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

25. 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

(B) Heat stored in the human body

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

26. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

Water will evaporate

27. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

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

Low boiling point

Large latent heat

Good electrical conductor

High risibility with oil

29. Freon group of refrigerants are

Toxic

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

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

Stirling

Bell Coleman

Carnot

Ericson

Page 4 of 4

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

Always more than unity

Any one of the above

Equal to unity

Always less than unity

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

2 bar

30 bar

8 bar

15 bar

33. 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)

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

Room air conditioners

Water coolers

Domestic refrigerators

All of these

35. 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

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

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

37. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

38. The vapour compression refrigerator employs the following cycle

Rankine

Carnot

Reversed Rankine

Reversed Carnot

39. 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

Ammonia

Brine

Freon

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

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

Superheat the vapour

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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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