Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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1. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

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

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

Back pressure

Suction pressure

Critical pressure

Discharge pressure

3. 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 secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

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

Wet vapour region

Sub-cooled liquid region

None of these

Superheated vapour region

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

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

Less

None of these

Same

7. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

8. 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

9. The lowest thermal diffusivity is of

Iron

Rubber

Aluminium

Lead

10. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

Not dependent on season

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

0.1 to 0.3 TR

5 to 7 TR

3 to 5 TR

1 to 3 TR

12. 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

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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

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

Tow specific heat of liquid

High boiling point

Higher critical temperature

High latent heat of vaporisation

15. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

16. 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

17. 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

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

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

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

None of the above

Is higher than that of the entering air

Is lower than that of the entering air

Can be lower or higher than that of the entering air

19. 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

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

Before entering the expansion valve

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

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

Reduce

Equalize

None of these

Increase

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

Zero

Any value

High, of the order of 25°

As low as possible (3 to 11°C)

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

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

Low weight per tonne of refrigeration

24. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Evaporator

Receiver

25. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Critical pressure of refrigerant

Much below critical pressure

Much above critical pressure

26. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Increases heat transfer rate

Is immaterial

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

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

The moisture present in it begins to condense

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

Bigger

Smaller

Equal

Smaller/bigger depending on capacity

29. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

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

Bootstrap air cooling system

Simple air cooling system

All of these

Simple evaporative air cooling system

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

32. Carbon dioxide is

Colourless

Non-flammable

Odourless

All of these

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

Equal to critical temperature

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

34. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Total heat lines

Entropy lines

Temperature lines

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

Sulphur dioxide

Fluorine

Carbon dioxide

Ammonia

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

All of these

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

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

Condenser

Expansion valve

Compressor

Evaporator

38. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

Increases

None of these

39. Choose the correct statement

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

Pre-cooling and sub-cooling bf refrigerant are same

Superheat and sensible heat of a refrigerant are same

A refrigerant should have low latent heat

40. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is equal to 1

Is more than 1

Refrigeration & Air-Conditioning Practice Set-2

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