Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. The optimum effective temperature for human comfort is

Same in winter and summer

Not dependent on season

Higher in winter than in summer

Lower in winter than in summer

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

Reduce

Increase

None of these

Equalize

3. The higher temperature in vapour compression cycle occurs at

Receiver

Evaporator

Compressor discharge

Expansion valve

4. 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

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

Sub-cooled liquid

Liquid

Saturated liquid

Wet vapour

6. The lowest thermal diffusivity is of

Iron

Rubber

Lead

Aluminium

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

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

All of these

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

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

Same

Less

None of these

10. 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

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11. During heating and dehumidification process, dry bulb temperature

None of these

Remains constant

Increases

Decreases

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

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

14. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

None of these

Increases

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

Between the combustion chamber and the first heat exchanger

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

Between the first heat exchanger and the secondary compressor

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

Condenser

Expansion valve

Compressor

Evaporator

17. Carbon dioxide is

Odourless

All of these

Non-flammable

Colourless

18. The COP of a domestic refrigerator

Depends upon the make

Is equal to 1

Is more than 1

Is less than 1

19. 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

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

Equal to critical temperature

Reduced to a value below its critical temperature

None of the above

Increased to a value above its critical temperature

Page 3 of 4

21. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Pressure lines

Total heat lines

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

Fluorine

Sulphur dioxide

Carbon dioxide

Ammonia

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

0.1 to 0.3 TR

5 to 7 TR

1 to 3 TR

3 to 5 TR

24. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

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

Smaller

Smaller/bigger depending on capacity

Bigger

Equal

26. 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

27. Choose the correct statement

A refrigerant should have low latent heat

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

Pre-cooling and sub-cooling bf refrigerant are same

28. 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

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

None of these

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

30. 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

Page 4 of 4

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

Simple evaporative air cooling system

Simple air cooling system

Bootstrap air cooling system

All of these

32. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

One tonne is the total mass of machine

One tonne refrigerant is used

One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min

33. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

Increases power required per ton of refrigeration

All of these

34. 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

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

Tow specific heat of liquid

Higher critical temperature

High latent heat of vaporisation

High boiling point

36. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much above critical pressure

Near critical pressure

Much below critical pressure

37. 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

38. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of cooling medium

Of freezing zone

At which refrigerant gas becomes liquid

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

Any value

As low as possible (3 to 11°C)

High, of the order of 25°

Zero

40. 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

(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

Refrigeration & Air-Conditioning Practice Set-2

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