Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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

Simple air cooling system

All of these

Simple evaporative air cooling system

Bootstrap air cooling system

2. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes solid

3. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Entropy lines

Pressure lines

4. The lowest thermal diffusivity is of

Rubber

Iron

Lead

Aluminium

5. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of cooling medium

Of freezing zone

At which refrigerant gas becomes liquid

6. 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

7. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Depends upon the make

Is less than 1

8. 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

9. 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

10. 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

Page 2 of 4

11. 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

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

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

Between the combustion chamber and the first heat exchanger

13. 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 refrigerant is used

One tonne is the total mass of machine

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

Back pressure

Discharge pressure

Suction pressure

Critical pressure

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

1 to 3 TR

3 to 5 TR

0.1 to 0.3 TR

5 to 7 TR

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

Equal

Bigger

Smaller/bigger depending on capacity

Smaller

17. 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

18. Choose the correct statement

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

A refrigerant should have low latent heat

19. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

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

Compressor

Expansion valve

Condenser

Evaporator

Page 3 of 4

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

Ammonia

Fluorine

Carbon dioxide

Sulphur dioxide

22. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

23. The dry bulb temperature during sensible heating of air

Remains constant

Increases

None of these

Decreases

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

Carbon dioxide

Lithium bromide

Sulphur dioxide

R-12

25. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Decreases

Remains constant

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

None of these

Less

Same

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

Liquid

Wet vapour

Saturated liquid

Sub-cooled liquid

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

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

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

None of these

Sub-cooled liquid region

Superheated vapour region

Wet vapour region

30. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Evaporator

Receiver

Expansion valve

Page 4 of 4

31. Carbon dioxide is

Colourless

Odourless

All of these

Non-flammable

32. 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

None of the above

Can be lower or higher than that of the entering air

33. 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

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

Before passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

After passing through the condenser

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

None of the above

The moisture present in it begins to condense

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

It is not affected by the moisture present in the air

36. 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

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

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

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

It is toxic to mucous membranes.

39. Reducing suction pressure in refrigeration cycle

All of these

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

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

None of the above

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

Equal to critical temperature

Refrigeration & Air-Conditioning Practice Set-2

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