Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. During heating and dehumidification process, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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

Less

Same

None of these

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

Sulphur dioxide

Ammonia

Carbon dioxide

Fluorine

4. 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 refrigeration effect to produce 1 ton of ice at NTP conditions

The cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

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

Back pressure

Discharge pressure

Suction pressure

Critical pressure

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

It is toxic to mucous membranes.

It reacts with copper and its alloys.

All of these

It requires large displacement per TR compared to fluoro carbons.

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

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

Higher coefficient of performance

8. 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

9. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

All of these

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

10. 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

Page 2 of 4

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

Smaller/bigger depending on capacity

Equal

Bigger

Smaller

12. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Is immaterial

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

13. The COP of a domestic refrigerator

Is less than 1

Depends upon the make

Is equal to 1

Is more than 1

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

Sub-cooled liquid

Wet vapour

Liquid

Saturated liquid

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

5 to 7 TR

1 to 3 TR

0.1 to 0.3 TR

3 to 5 TR

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

High pressure liquid refrigerant

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

17. 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

Ammonia vapour is driven out of solution

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

High, of the order of 25°

Any value

As low as possible (3 to 11°C)

Zero

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

Equal to critical temperature

20. The lowest thermal diffusivity is of

Lead

Iron

Aluminium

Rubber

Page 3 of 4

21. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Pressure lines

Total heat lines

22. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Not dependent on season

Same in winter and summer

23. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

None of these

Increases

24. 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

25. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

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

None of these

Reduce

Increase

Equalize

28. Carbon dioxide is

Odourless

Non-flammable

All of these

Colourless

29. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Receiver

Compressor discharge

30. 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

Page 4 of 4

31. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

If operating temperature of system is low, then refrigerant with low boiling point should be used

32. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

33. A one tonne refrigerating machine means that

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

One tonne is the total mass of machine

34. 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

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

Compressor

Condenser

Expansion valve

Evaporator

36. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Critical pressure of refrigerant

Near critical pressure

Much below critical pressure

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

None of the above

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

38. 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

39. 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

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

Sulphur dioxide

R-12

Carbon dioxide

Lithium bromide

Refrigeration & Air-Conditioning Practice Set-2

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