Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

2. The vapour compression refrigerator employs the following cycle

Reversed Carnot

Rankine

Carnot

Reversed Rankine

3. 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

2.33

1.33

3.33

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

Ammonia

Brine

Carbon dioxide

Freon

5. 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

6. 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

Positive

Negative

None of these

Zero

7. 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

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

15°C

20°C

10°C

5°C

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

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

Condenser tubes

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

Optimum

Any value

High

Low

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

Always more than unity

Equal to unity

Always less than unity

Any one of the above

12. The curved lines on a psychrometric chart indicates

Relative humidity

Dew point temperature

Dry bulb temperature

Wet bulb temperature

13. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

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

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

14. The boiling point of ammonia is

-77.7°C

-10.5°C

-30°C

-33.3°C

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

Less

More for small capacity and less for high capacity

Same

16. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

17. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

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

Bell Coleman

Stirling

Carnot

Ericson

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

0.1 ton

10 tons

40 tons

5 tons

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

Page 3 of 4

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

Evaporator and compressor

Compressor and condenser

Condenser and receiver

Receiver and evaporator

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

0.67

0.6

0.376

0.4

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

2 bar

15 bar

8 bar

30 bar

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

All of these

Room air conditioners

Domestic refrigerators

Water coolers

26. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

27. 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

28. 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

Super-cooling

None of these

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

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

Absorber

30. 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

Page 4 of 4

31. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Miniature sealed unit

Axial

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

High risibility with oil

Large latent heat

Good electrical conductor

Low boiling point

33. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

Toxic

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

1 to 2 h.p. per ton of refrigeration

35. 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

36. 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.

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

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

38. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Three heat exchangers

Two heat exchangers

39. 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 pressure

Takes place at constant entropy

Involves no change in volume

40. In a lithium bromide absorption refrigeration system

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

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

None of these

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

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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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