Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. A thermostatic expansion valve in a refrigeration system

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

None of the above

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

5°C

20°C

15°C

10°C

3. 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

0.376

0.6

4. Critical temperature is the temperature above which

Water will evaporate

A gas will immediately liquefy

A gas will never liquefy

Water will never evaporate

5. 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

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

Water coolers

Room air conditioners

Domestic refrigerators

All of these

7. The boiling point of ammonia is

-30°C

-77.7°C

-10.5°C

-33.3°C

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

0.2

1.2

9. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

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

Ericson

Carnot

Bell Coleman

Stirling

Page 2 of 4

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

Collect vapours

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

12. 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

13. 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.

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

Condenser tubes

Evaporator tubes

Capillary tubes

Refrigerant cooling tubes

15. 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

16. 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

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

17. 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

Ammonia

Freon

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

More for small capacity and less for high capacity

Same

Less

19. 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

9: 1

1: 1

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

Receiver and evaporator

Condenser and receiver

Compressor and condenser

Evaporator and compressor

Page 3 of 4

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

Any one of the above

Always less than unity

Always more than unity

Equal to unity

22. 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

3.33

1.33

23. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

Two heat exchangers

One heat exchanger

24. The domestic refrigerator uses following type of compressor

Axial

Piston type reciprocating

Miniature sealed unit

Centrifugal

25. 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

26. The curved lines on a psychrometric chart indicates

Dew point temperature

Dry bulb temperature

Wet bulb temperature

Relative humidity

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

Absorber

Evaporator

Condenser, absorber and separator (rectifier)

Condenser

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

Superheated vapour

Saturated liquid

Dry saturated vapour

Wet vapour

29. 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

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

None of these

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

10 tons

0.1 ton

5 tons

40 tons

Page 4 of 4

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

2 bar

15 bar

30 bar

8 bar

32. Freon group of refrigerants are

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

Toxic

33. 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

None of these

Negative

Zero

34. The freezing point of sulphur dioxide is

-56.6°C

-135.8°C

-77.7°C

-75.2°C

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

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

36. 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

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

(A) Heat dissipated to the surroundings

37. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

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

Optimum

High

Low

Any value

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

Large latent heat

Good electrical conductor

Low boiling point

High risibility with oil

40. 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 entropy

Takes place at constant pressure

Involves no change in volume

Share this Now with Friends:

VideRime

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

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection