Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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1. 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

2. During heating and dehumidification process, dry bulb temperature

Increases

Remains constant

Decreases

None of these

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

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

Fluorine

Carbon dioxide

Ammonia

Sulphur dioxide

5. Formation of frost on evaporator in refrigerator

Is immaterial

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

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

Less

None of these

Same

7. Carbon dioxide is

Colourless

All of these

Odourless

Non-flammable

8. A one tonne refrigerating machine means that

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 is the total mass of machine

One tonne refrigerant is used

One tonne of water can be converted into ice

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

Expansion valve

Evaporator

Condenser

Compressor

10. The optimum effective temperature for human comfort is

Higher in winter than in summer

Same in winter and summer

Not dependent on season

Lower in winter than in summer

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11. 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

12. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Receiver

Compressor discharge

13. 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

Equalize

Reduce

Increase

14. The lowest thermal diffusivity is of

Iron

Aluminium

Rubber

Lead

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

Low weight per tonne of refrigeration

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

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

1 to 3 TR

0.1 to 0.3 TR

3 to 5 TR

5 to 7 TR

17. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

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

Wet vapour

Sub-cooled liquid

Saturated liquid

Liquid

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

High, of the order of 25°

Any value

Zero

As low as possible (3 to 11°C)

20. The dry bulb temperature during sensible heating of air

None of these

Decreases

Remains constant

Increases

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

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

Smaller/bigger depending on capacity

Bigger

Equal

Smaller

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

None of the above

Can be lower or higher than that of the entering air

Is lower than that of the entering air

Is higher than that of the entering air

24. 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 - 1

(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

25. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

Much above critical pressure

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

Carbon dioxide

Sulphur dioxide

R-12

Lithium bromide

27. Choose the correct statement

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

Superheat and sensible heat of a refrigerant are same

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

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

Higher critical temperature

High latent heat of vaporisation

High boiling point

Tow specific heat of liquid

29. 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

30. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes solid

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

Simple air cooling system

All of these

Bootstrap air cooling system

Simple evaporative air cooling system

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

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

None of the above

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

Sub-cooled liquid region

Superheated vapour region

Wet vapour region

None of these

34. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Entropy lines

Pressure lines

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

Critical pressure

Suction pressure

Back pressure

Discharge pressure

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

It reacts with copper and its alloys.

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

All of these

37. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Is equal to 1

Depends upon the make

38. One ton of the refrigeration is

The standard unit used in refrigeration problems

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 cooling effect produced by melting 1 ton of ice

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

40. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

Of cooling medium

Refrigeration & Air-Conditioning Practice Set-2

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