Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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1. Presence of moisture in a refrigerant affects the working of

Compressor

Evaporator

Condenser

Expansion valve

2. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

3. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

4. If a gas is to be liquefied, its temperature must be

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

5. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents

Sub-cooled liquid region

None of these

Superheated vapour region

Wet vapour region

6. Dry bulb temperature is the temperature of air recorded by a thermometer, when

It is not affected by the moisture present in the air

None of the above

The moisture present in it begins to condense

Its bulb is surrounded by a wet cloth exposed to the air

7. Which of the following statement is correct for ammonia as a refrigerant?

It reacts with copper and its alloys.

All of these

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

8. In a bootstrap air evaporative cooling system, the evaporator is provided

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

9. The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.

Same

Less

None of these

10. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be

More/less depending on rating

Same

Less

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11. The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and

Lithium bromide

Sulphur dioxide

R-12

Carbon dioxide

12. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid will remain liquid

13. Condensing temperature in a refrigerator is the temperature

Of cooling medium

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

14. Carbon dioxide is

Non-flammable

Colourless

All of these

Odourless

15. The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by

(C.O.P.)_P = (C.O.P.)_R + 2

(C.O.P)_P = (C.O.P)_R - 1

(C.O.P)_P = (C.O.P)_R

(C.O.P.)_P = (C.O.P.)_R + 1

16. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

Much below critical pressure

17. The optimum effective temperature for human comfort is

Same in winter and summer

Not dependent on season

Lower in winter than in summer

Higher in winter than in summer

18. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

19. The evaporator changes the low pressure liquid refrigerant from the expansion valve into

Low pressure vapour refrigerant

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

None of these

20. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

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21. One ton of the refrigeration is

The refrigeration effect to produce 1 ton of ice at NTP conditions

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

22. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is equal to 1

Is less than 1

23. The dry bulb temperature during sensible heating of air

Increases

Remains constant

None of these

Decreases

24. The capacity of a domestic refrigerator is in the range of

5 to 7 TR

3 to 5 TR

0.1 to 0.3 TR

1 to 3 TR

25. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is

Smaller

Equal

Smaller/bigger depending on capacity

Bigger

26. The pressure at the inlet of a refrigerant compressor is called

Back pressure

Suction pressure

Critical pressure

Discharge pressure

27. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.

Equalize

Increase

Reduce

None of these

28. In refrigerators, the temperature difference between the evaporating refrigerant and the medium being cooled should be

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

Zero

29. In a vapour compression cycle, the refrigerant immediately after expansion valve is

Wet vapour

Sub-cooled liquid

Liquid

Saturated liquid

30. During heating and humidification, the final relative humidity of air

None of the above

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

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31. Which of the following refrigerant has the maximum ozone depletion potential in the stratosphere?

Carbon dioxide

Fluorine

Ammonia

Sulphur dioxide

32. The evolution of heat of solution takes place in ammonia absorption plant when

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

33. In aircraft, air refrigeration Cycle is used because of

Low temperature at high altitudes

High heat transfer rate

Low weight per tonne of refrigeration

Higher coefficient of performance

34. The air cooling system mostly used in transport type aircrafts is

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

Simple air cooling system

35. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid

Before passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

36. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

37. Choose the correct statement

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

If operating temperature of system is low, then refrigerant with low boiling point should be used

Superheat and sensible heat of a refrigerant are same

38. A one tonne refrigerating machine means that

One tonne refrigerant is used

One tonne is the total mass of machine

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

One tonne of water can be converted into ice

39. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Compressor discharge

Receiver

40. Pick up the wrong statement. A refrigerant should have

Tow specific heat of liquid

High latent heat of vaporisation

High boiling point

Higher critical temperature

Refrigeration & Air-Conditioning Practice Set-2

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