Refrigeration & Air-Conditioning Practice Set-2

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

Suction pressure

Critical pressure

Back pressure

Discharge pressure

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

Liquid

Wet vapour

Sub-cooled liquid

Saturated liquid

3. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

5. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Temperature lines

Pressure lines

Total heat lines

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

Smaller/bigger depending on capacity

Bigger

Smaller

Equal

7. 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

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

Increase

None of these

Equalize

Reduce

9. The dry bulb temperature during sensible heating of air

Increases

Decreases

None of these

Remains constant

10. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Much below critical pressure

Critical pressure of refrigerant

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11. The lowest thermal diffusivity is of

Iron

Lead

Rubber

Aluminium

12. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Is immaterial

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

13. 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 produce 1 ton of ice at NTP conditions

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

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

Same

More

None of these

Less

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

None of the above

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

Compressor

Expansion valve

Evaporator

Condenser

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 - 1

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

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

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

It is toxic to mucous membranes.

It reacts with copper and its alloys.

All of these

It requires large displacement per TR compared to fluoro carbons.

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

Sulphur dioxide

Lithium bromide

R-12

Carbon dioxide

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

All of these

Simple air cooling system

Simple evaporative air cooling system

Bootstrap air cooling system

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21. The optimum effective temperature for human comfort is

Not dependent on season

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

22. 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

23. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

24. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Receiver

Compressor discharge

25. 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

26. 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

Is lower than that of the entering air

None of the above

27. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Depends upon the make

Is less than 1

28. 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

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

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

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

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

After passing through the expansion or throttle valve

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

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

None of these

Low pressure vapour refrigerant

32. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

All of these

Lowers evaporation temperature

Increases power required per ton of refrigeration

33. A one tonne refrigerating machine means that

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 is the total mass of machine

One tonne refrigerant is used

34. 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

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

Same

Less

More/less depending on rating

More

36. 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

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

Superheated vapour region

Wet vapour region

Sub-cooled liquid region

None of these

38. Carbon dioxide is

All of these

Colourless

Non-flammable

Odourless

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

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

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

Any value

Refrigeration & Air-Conditioning Practice Set-2

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