Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

Compressor and condenser

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

Domestic refrigerators

All of these

Water coolers

Room air conditioners

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

High

Any value

Low

Optimum

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

Super-cooling

Normal cooling

None of these

Sub-cooling or under-cooling

5. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

6. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

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

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

Absorber

8. 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

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

Wet vapour

Dry saturated vapour

Superheated vapour

Saturated liquid

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

Condenser tubes

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Page 2 of 4

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

Low boiling point

Large latent heat

High risibility with oil

Good electrical conductor

12. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

Much below critical temperature

13. The freezing point of sulphur dioxide is

-135.8°C

-56.6°C

-75.2°C

-77.7°C

14. 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 temperature

Takes place at constant pressure

Takes place at constant entropy

15. 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

0.376

0.4

0.67

16. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

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

Less

Same

More for small capacity and less for high capacity

18. In a lithium bromide absorption refrigeration system

None of these

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

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

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

19. 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

Ammonia

Carbon dioxide

Freon

20. 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

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

Page 3 of 4

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

Wet bulb temperature of air

Dry bulb temperature of air

Dew point temperature of air

Ambient air temperature

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

10 tons

0.1 ton

40 tons

5 tons

23. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

Inflammable

24. 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

1.25

2.15

5.12

25. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

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

Stirling

Bell Coleman

Ericson

Carnot

27. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

28. 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

Zero

Negative

Positive

29. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

30. The boiling point of ammonia is

-77.7°C

-30°C

-10.5°C

-33.3°C

Page 4 of 4

31. 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

32. 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)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

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

Superheat the vapour

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

34. 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.

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

8 bar

15 bar

30 bar

2 bar

36. 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

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

Always less than unity

Always more than unity

Any one of the above

Equal to unity

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

1: 9

9: 1

1: 1

1: 3

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

20°C

10°C

5°C

15°C

40. 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)

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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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