Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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1. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

3 to 5 TR

1 to 3 TR

0.1 to 0.3 TR

5 to 7 TR

3. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

None of these

Increases

4. Choose the correct statement

A refrigerant should have low latent heat

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

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

Can be lower or higher than that of the entering air

None of the above

Is higher than that of the entering air

Is lower than that of the entering air

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

None of these

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

7. Formation of frost on evaporator in refrigerator

Is immaterial

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

8. 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

None of the above

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

9. 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

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

Simple evaporative air cooling system

Simple air cooling system

All of these

Bootstrap air cooling system

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

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

High heat transfer rate

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 + 2

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

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

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

Sulphur dioxide

Carbon dioxide

Ammonia

Fluorine

14. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

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

Expansion valve

Condenser

Evaporator

Compressor

16. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Expansion valve

Evaporator

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

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

High boiling point

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

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

None of these

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

Wet vapour

Liquid

Sub-cooled liquid

Saturated liquid

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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21. 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

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

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

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

None of these

Less

Same

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

Discharge pressure

Back pressure

Suction pressure

Critical pressure

26. A one tonne refrigerating machine means that

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 refrigerant is used

One tonne of water can be converted into ice

27. 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

28. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

29. The optimum effective temperature for human comfort is

Higher in winter than in summer

Same in winter and summer

Lower in winter than in summer

Not dependent on season

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

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31. The lowest thermal diffusivity is of

Aluminium

Lead

Iron

Rubber

32. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

33. One ton of the refrigeration is

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

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 cooling effect produced by melting 1 ton of ice

34. 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

35. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

36. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

All of these

Lowers evaporation temperature

37. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Entropy lines

Pressure lines

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

High, of the order of 25°

Zero

Any value

As low as possible (3 to 11°C)

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

Equal

Bigger

Smaller

Smaller/bigger depending on capacity

40. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

Refrigeration & Air-Conditioning Practice Set-2

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