Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

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

Good electrical conductor

Large latent heat

High risibility with oil

Low boiling point

3. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

Inflammable

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

High

Low

Any value

Optimum

5. 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

6. A thermostatic expansion valve in a refrigeration system

None of the above

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

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

Condenser tubes

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

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

40 tons

5 tons

0.1 ton

10 tons

9. 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

10. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will evaporate

Water will never evaporate

Page 2 of 4

11. Which of the following statement is correct?

(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.

(D) Both (A) and (B)

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

Compressor and condenser

Condenser and receiver

Receiver and evaporator

Evaporator and compressor

13. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

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

8 bar

15 bar

30 bar

2 bar

15. 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

16. 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

(A) Heat dissipated to the surroundings

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

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

0.376

0.6

0.67

0.4

18. 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

19. 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

1 to 2 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

20. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Piston type reciprocating

Axial

Centrifugal

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21. 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: 1

1: 3

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

Ericson

Bell Coleman

Stirling

Carnot

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

Equally

Unpredictable

Less

24. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

25. 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

Zero

None of these

26. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

At critical Temperature

27. 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

28. In a lithium bromide absorption refrigeration system

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

Water 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

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

5°C

15°C

20°C

10°C

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

Water coolers

All of these

Room air conditioners

Domestic refrigerators

Page 4 of 4

31. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

Three heat exchangers

One heat exchanger

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

1.33

2.33

4.33

33. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-75.2°C

-77.7°C

34. The boiling point of ammonia is

-77.7°C

-33.3°C

-10.5°C

-30°C

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

Condenser, absorber and separator (rectifier)

Evaporator

Absorber

Condenser

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

Same

Less

More for small capacity and less for high capacity

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 entropy

Takes place at constant temperature

Takes place at constant pressure

38. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

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

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

Collect vapours

Detect liquid in vapour

40. 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

Brine

Ammonia

Carbon dioxide

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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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