Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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Page 1 of 4

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

Any one of the above

Always more than unity

Always less than unity

Equal to unity

2. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Axial

Piston type reciprocating

3. 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

4. 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

Negative

Zero

Positive

5. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Toxic

Non-inflammable and toxic

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

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

Condenser

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

Domestic refrigerators

Room air conditioners

Water coolers

All of these

8. 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

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

Same

More for small capacity and less for high capacity

Less

10. 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

Page 2 of 4

11. 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

Freon

Ammonia

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

Compressor and condenser

Receiver and evaporator

Evaporator and compressor

Condenser and receiver

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

Capillary tubes

Refrigerant cooling tubes

Evaporator tubes

Condenser tubes

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

1: 3

1: 9

1: 1

9: 1

15. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Near critical temperature of refrigerant

Much below critical temperature

Above critical temperature

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

High risibility with oil

Good electrical conductor

Large latent heat

Low boiling point

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

Bell Coleman

Ericson

Stirling

Carnot

18. The boiling point of ammonia is

-33.3°C

-30°C

-10.5°C

-77.7°C

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

40 tons

5 tons

10 tons

0.1 ton

20. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Reversed Rankine

Carnot

Rankine

Page 3 of 4

21. 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)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

(T₂ - T₁)/T₁

22. 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

0.67

0.4

0.376

23. 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

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

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

25. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

26. 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

27. A bootstrap air cooling system has

Three heat exchangers

Two heat exchangers

Four heat exchangers

One heat exchanger

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

Sub-cooling or under-cooling

None of these

Normal cooling

Super-cooling

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

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

30. 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

3.33

2.33

1.33

Page 4 of 4

31. 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

32. A thermostatic expansion valve in a refrigeration system

None of the above

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

33. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-56.6°C

-135.8°C

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

20°C

5°C

10°C

15°C

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

Low

Optimum

Any value

High

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

8 bar

2 bar

15 bar

30 bar

37. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

38. Critical temperature is the temperature above which

Water will never evaporate

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

39. 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

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

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

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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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