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

Weak solution mixes with strong solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

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

Can be lower or higher than that of the entering air

Is higher than that of the entering air

None of the above

Is lower than that of the entering air

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

Equal to critical temperature

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

4. Condensing temperature in a refrigerator is the temperature

Of evaporator

At which refrigerant gas becomes liquid

Of freezing zone

Of cooling medium

5. 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

6. 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.

7. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

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

Smaller/bigger depending on capacity

Smaller

Bigger

Equal

9. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes solid

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

Less

Same

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

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

The moisture present in it begins to condense

None of the above

It is not affected by the moisture present in the air

12. 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 - 1

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

13. 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

14. The lowest thermal diffusivity is of

Lead

Rubber

Iron

Aluminium

15. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

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

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

17. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

18. One ton of the refrigeration is

The standard unit used in refrigeration problems

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

The cooling effect produced by melting 1 ton of ice

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

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

None of these

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

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

Carbon dioxide

R-12

Lithium bromide

Sulphur dioxide

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21. 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

22. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

Increases

None of these

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

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

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

25. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Pressure lines

Entropy lines

Total heat lines

26. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

Lowers evaporation temperature

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

Low temperature at high altitudes

Low weight per tonne of refrigeration

Higher coefficient of performance

High heat transfer rate

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

Expansion valve

Compressor

Condenser

Evaporator

29. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is equal to 1

Is less than 1

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

Saturated liquid

Liquid

Wet vapour

Sub-cooled liquid

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31. 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

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

Same

None of these

Less

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

Bootstrap air cooling system

All of these

Simple evaporative air cooling system

Simple air cooling system

34. Carbon dioxide is

Non-flammable

All of these

Odourless

Colourless

35. 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

36. 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

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

Sub-cooled liquid region

Superheated vapour region

None of these

Wet vapour region

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

Ammonia

Sulphur dioxide

Carbon dioxide

Fluorine

39. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Compressor discharge

Receiver

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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