Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

2. 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 refrigerant is used

One tonne is the total mass of machine

One tonne of water can be converted into ice

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

Less

Same

More/less depending on rating

4. Formation of frost on evaporator in refrigerator

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

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

High, of the order of 25°

As low as possible (3 to 11°C)

Zero

Any value

6. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

7. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Evaporator

Receiver

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

Simple evaporative air cooling system

Bootstrap air cooling system

All of these

Simple air cooling system

9. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

10. 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

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11. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

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

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

Sulphur dioxide

Fluorine

Ammonia

Carbon dioxide

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

Same

None of these

Less

14. The COP of a domestic refrigerator

Is more than 1

Is less than 1

Is equal to 1

Depends upon the make

15. 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

Before entering the expansion valve

After passing through the condenser

16. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

Increases

None of these

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

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

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

19. 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

None of the above

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

3 to 5 TR

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

Page 3 of 4

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

None of these

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

22. The lowest thermal diffusivity is of

Aluminium

Lead

Iron

Rubber

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

Expansion valve

Condenser

Evaporator

Compressor

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

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

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

25. The optimum effective temperature for human comfort is

Lower in winter than in summer

Same in winter and summer

Higher in winter than in summer

Not dependent on season

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

High latent heat of vaporisation

High boiling point

Tow specific heat of liquid

Higher critical temperature

27. During heating and dehumidification process, dry bulb temperature

Increases

None of these

Remains constant

Decreases

28. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Temperature lines

Pressure lines

Total heat lines

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

Bigger

Equal

Smaller

Smaller/bigger depending on capacity

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

None of these

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

Page 4 of 4

31. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

Lowers compressor capacity because vapour is lighter

32. 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

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

Is lower than that of the entering air

None of the above

Is higher than that of the entering air

Can be lower or higher than that of the entering air

34. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid becomes solid

35. Carbon dioxide is

Colourless

Non-flammable

Odourless

All of these

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

Sulphur dioxide

Carbon dioxide

R-12

Lithium bromide

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

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

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

Suction pressure

Discharge pressure

Critical pressure

Back pressure

40. 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

Reduce

Equalize

Refrigeration & Air-Conditioning Practice Set-2

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