Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Any value

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

2. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

Much below critical pressure

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

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

Before passing through the condenser

4. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid becomes vapour

5. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Entropy lines

Temperature lines

Pressure lines

6. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Can be avoided by proper design

Is immaterial

Results in loss of heat due to poor heat transfer

7. The dry bulb temperature during sensible heating of air

Decreases

Increases

Remains constant

None of these

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

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

Increased to a value above its critical temperature

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

Carbon dioxide

Sulphur dioxide

Fluorine

Ammonia

10. One ton of the refrigeration is

The standard unit used in refrigeration problems

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

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

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11. 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

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

It requires large displacement per TR compared to fluoro carbons.

All of these

It reacts with copper and its alloys.

It is toxic to mucous membranes.

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

Carbon dioxide

Lithium bromide

R-12

Sulphur dioxide

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

Is lower than that of the entering air

Is higher than that of the entering air

Can be lower or higher than that of the entering air

None of the above

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

Low weight per tonne of refrigeration

Higher coefficient of performance

High heat transfer rate

Low temperature at high altitudes

16. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

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

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

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

Smaller

Equal

Bigger

Smaller/bigger depending on capacity

19. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

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

Page 3 of 4

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

Higher critical temperature

High boiling point

Tow specific heat of liquid

High latent heat of vaporisation

22. 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

23. 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

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 + 2

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

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

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

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

None of these

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

Condenser

Expansion valve

Compressor

Evaporator

27. The optimum effective temperature for human comfort is

Higher in winter than in summer

Not dependent on season

Lower in winter than in summer

Same in winter and summer

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

Discharge pressure

Critical pressure

Suction pressure

Back pressure

29. 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

30. 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

Page 4 of 4

31. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

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

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

5 to 7 TR

33. 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

The moisture present in it begins to condense

None of the above

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

Equalize

Reduce

Increase

None of these

35. The lowest thermal diffusivity is of

Lead

Iron

Rubber

Aluminium

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

Same

None of these

Less

37. The COP of a domestic refrigerator

Depends upon the make

Is less than 1

Is more than 1

Is equal to 1

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

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

None of these

39. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

Wet vapour

Sub-cooled liquid

Liquid

Saturated liquid

Refrigeration & Air-Conditioning Practice Set-2

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