Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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1. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Entropy lines

Temperature lines

Pressure lines

2. Carbon dioxide is

Colourless

All of these

Non-flammable

Odourless

3. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

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

Between the second heat exchanger and the cooling turbine

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

Back pressure

Suction pressure

Critical pressure

Discharge pressure

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

Less

More/less depending on rating

Same

7. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Increases power required per ton of refrigeration

All of these

Lowers compressor capacity because vapour is lighter

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

Superheated vapour region

Wet vapour region

None of these

Sub-cooled liquid region

9. 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

10. 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

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11. During heating and dehumidification process, dry bulb temperature

Decreases

None of these

Remains constant

Increases

12. The dry bulb temperature during sensible heating of air

Remains constant

Decreases

None of these

Increases

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

After passing through the expansion or throttle valve

After passing through the condenser

Before passing through the condenser

Before entering the expansion valve

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

Expansion valve

Compressor

Evaporator

Condenser

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

High boiling point

Higher critical temperature

Tow specific heat of liquid

High latent heat of vaporisation

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

Liquid

Sub-cooled liquid

Saturated liquid

Wet vapour

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

It requires large displacement per TR compared to fluoro carbons.

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

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

Low pressure vapour refrigerant

High pressure liquid refrigerant

None of these

Low pressure liquid and vapour refrigerant

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

Simple air cooling system

Bootstrap air cooling system

All of these

Simple evaporative air cooling system

20. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

At which refrigerant gas becomes liquid

Of evaporator

Page 3 of 4

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

Reduce

Increase

Equalize

None of these

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

Lithium bromide

R-12

Carbon dioxide

Sulphur dioxide

23. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne refrigerant is used

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

24. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

25. 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

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

None of these

Same

Less

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

Is higher than that of the entering air

None of the above

Can be lower or higher than that of the entering air

Is lower than that of the entering air

28. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Critical pressure of refrigerant

Near critical pressure

Much above critical pressure

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

Smaller

Equal

Bigger

Smaller/bigger depending on capacity

30. 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 + 2

(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

Page 4 of 4

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

Sulphur dioxide

Fluorine

Ammonia

Carbon dioxide

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

It is not affected by the moisture present in the air

The moisture present in it begins to condense

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

None of the above

33. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Can be avoided by proper design

Is immaterial

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

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

35. Choose the correct statement

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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

36. One ton of the refrigeration is

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

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

The standard unit used in refrigeration problems

37. The lowest thermal diffusivity is of

Lead

Iron

Aluminium

Rubber

38. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Receiver

Evaporator

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

Zero

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

40. The optimum effective temperature for human comfort is

Higher in winter than in summer

Same in winter and summer

Not dependent on season

Lower in winter than in summer

Refrigeration & Air-Conditioning Practice Set-2

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