Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. 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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

Superheated vapour region

None of these

Sub-cooled liquid region

Wet vapour region

3. 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

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

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

5. 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

6. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

Increases

None of these

7. The dry bulb temperature during sensible heating of air

None of these

Increases

Decreases

Remains constant

8. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

9. Carbon dioxide is

Non-flammable

Odourless

All of these

Colourless

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

Fluorine

Carbon dioxide

Ammonia

Sulphur dioxide

Page 2 of 4

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

Equal

Smaller

Bigger

Smaller/bigger depending on capacity

12. 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

None of the above

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

13. 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 - 1

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

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

None of these

Same

Less

15. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

Of evaporator

At which refrigerant gas becomes liquid

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

Increase

Reduce

Equalize

None of these

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

Can be lower or higher than that of the entering air

Is lower than that of the entering air

None of the above

Is higher than that of the entering air

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

More/less depending on rating

Less

Same

19. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Depends upon the make

Is less than 1

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

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

Between the second heat exchanger and the cooling turbine

Page 3 of 4

21. 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

22. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Pressure lines

Total heat lines

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

Saturated liquid

Liquid

Wet vapour

Sub-cooled liquid

24. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Higher critical temperature

High latent heat of vaporisation

Tow specific heat of liquid

High boiling point

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

3 to 5 TR

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

27. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

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

Expansion valve

Evaporator

Condenser

Compressor

29. The lowest thermal diffusivity is of

Aluminium

Iron

Rubber

Lead

30. One ton of the refrigeration is

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

The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

Page 4 of 4

31. 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.

It reacts with copper and its alloys.

All of these

32. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Expansion valve

Receiver

Evaporator

33. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

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

Suction pressure

Discharge pressure

Back pressure

Critical pressure

35. 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

36. 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

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

As low as possible (3 to 11°C)

Zero

Any value

High, of the order of 25°

38. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne of water can be converted into ice

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

39. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

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

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Refrigeration & Air-Conditioning Practice Set-2

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