Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Same

More/less depending on rating

Less

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

Lithium bromide

Sulphur dioxide

Carbon dioxide

R-12

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

None of these

Sub-cooled liquid region

Superheated vapour region

Wet vapour region

4. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Smaller/bigger depending on capacity

Bigger

Equal

Smaller

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

0.1 to 0.3 TR

1 to 3 TR

5 to 7 TR

3 to 5 TR

7. Carbon dioxide is

Odourless

Non-flammable

All of these

Colourless

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

None of these

Increase

Equalize

Reduce

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

Condenser

Evaporator

Compressor

Expansion valve

10. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

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

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

High pressure liquid refrigerant

12. The optimum effective temperature for human comfort is

Same in winter and summer

Lower in winter than in summer

Not dependent on season

Higher in winter than in summer

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

Critical pressure

Suction pressure

Back pressure

Discharge pressure

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

It requires large displacement per TR compared to fluoro carbons.

All of these

It reacts with copper and its alloys.

It is toxic to mucous membranes.

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

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

Bootstrap air cooling system

Simple evaporative air cooling system

Simple air cooling system

All of these

17. The lowest thermal diffusivity is of

Iron

Aluminium

Lead

Rubber

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

None of the above

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

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

Low weight per tonne of refrigeration

20. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

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21. 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

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

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

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

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

Wet vapour

Sub-cooled liquid

Liquid

Saturated liquid

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

Less

None of these

Same

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

Carbon dioxide

Sulphur dioxide

Fluorine

Ammonia

25. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne of water can be converted into ice

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 refrigerant is used

26. Condensing temperature in a refrigerator is the temperature

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

Of freezing zone

27. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Compressor discharge

Receiver

28. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

Is immaterial

29. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

30. The dry bulb temperature during sensible heating of air

Remains constant

None of these

Increases

Decreases

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

Between the secondary compressor and the second heat exchanger

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

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

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

33. Choose the correct statement

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

A refrigerant should have low latent heat

34. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Entropy lines

Total heat lines

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

Is higher than that of the entering air

None of the above

Can be lower or higher than that of the entering air

Is lower than that of the entering air

36. During heating and dehumidification process, dry bulb temperature

Remains constant

None of these

Increases

Decreases

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

Any value

High, of the order of 25°

Zero

As low as possible (3 to 11°C)

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

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

39. One ton of the refrigeration is

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

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

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

Tow specific heat of liquid

Higher critical temperature

High boiling point

High latent heat of vaporisation

Refrigeration & Air-Conditioning Practice Set-2

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