Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

Above critical temperature

Much below critical temperature

At critical Temperature

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

Domestic refrigerators

All of these

Water coolers

Room air conditioners

3. 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

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

Superheated vapour

Wet vapour

Dry saturated vapour

Saturated liquid

5. 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

Superheat the vapour

Detect liquid in vapour

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

Condenser

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

7. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

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

Optimum

High

Any value

Low

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

Always more than unity

Equal to unity

Any one of the above

Always less than unity

10. The boiling point of ammonia is

-77.7°C

-10.5°C

-30°C

-33.3°C

Page 2 of 4

11. A thermostatic expansion valve in a refrigeration system

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

None of the above

12. 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.

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

Low boiling point

High risibility with oil

Large latent heat

Good electrical conductor

14. 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

2.33

3.33

1.33

4.33

15. 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: 3

9: 1

1: 9

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

30 bar

15 bar

2 bar

8 bar

17. A bootstrap air cooling system has

Two heat exchangers

Four heat exchangers

Three heat exchangers

One heat exchanger

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

40 tons

10 tons

5 tons

0.1 ton

19. The curved lines on a psychrometric chart indicates

Dew point temperature

Relative humidity

Wet bulb temperature

Dry bulb temperature

20. 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

Zero

None of these

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)

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

22. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Nontoxic and non-inflammable

Toxic

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

Takes place at constant entropy

Takes place at constant pressure

Involves no change in volume

Takes place at constant temperature

24. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Carnot

Reversed Rankine

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

Ericson

Bell Coleman

Stirling

Carnot

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

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

Capillary tubes

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

Unpredictable

Less

Equally

28. The freezing point of sulphur dioxide is

-56.6°C

-75.2°C

-135.8°C

-77.7°C

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

Receiver and evaporator

Condenser and receiver

Compressor and condenser

Evaporator and compressor

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

15°C

10°C

20°C

5°C

Page 4 of 4

31. 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

Carbon dioxide

Brine

Ammonia

32. In a lithium bromide absorption refrigeration system

None of these

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

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

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

33. 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

34. 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

0.4

0.6

0.376

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

Dew point temperature of air

Wet bulb temperature of air

Ambient air temperature

Dry bulb temperature of air

37. 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

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

Less

More for small capacity and less for high capacity

Same

39. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

Water will evaporate

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

Normal cooling

None of these

Super-cooling

Sub-cooling or under-cooling

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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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