Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

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Page 1 of 4

1. The lowest thermal diffusivity is of

Rubber

Lead

Iron

Aluminium

2. 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

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

4. 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

5. Choose the correct statement

A refrigerant should have low latent heat

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

6. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

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

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

High pressure liquid refrigerant

8. The higher temperature in vapour compression cycle occurs at

Expansion valve

Receiver

Compressor discharge

Evaporator

9. 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

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

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Page 2 of 4

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

The moisture present in it begins to condense

None of the above

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

It is not affected by the moisture present in the air

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

Is lower than that of the entering air

Can be lower or higher than that of the entering air

Is higher than that of the entering air

None of the above

13. The COP of a domestic refrigerator

Depends upon the make

Is more than 1

Is equal to 1

Is less than 1

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

Bigger

Equal

Smaller/bigger depending on capacity

Smaller

15. The dry bulb temperature during sensible heating of air

Decreases

Remains constant

None of these

Increases

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

Same

More/less depending on rating

Less

17. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Entropy lines

Pressure lines

Temperature lines

18. Carbon dioxide is

Odourless

Colourless

All of these

Non-flammable

19. 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

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

Higher coefficient of performance

Low temperature at high altitudes

High heat transfer rate

Low weight per tonne of refrigeration

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.

None of these

Reduce

Increase

Equalize

22. 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

After passing through the condenser

Before entering the expansion valve

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

Liquid

Saturated liquid

Wet vapour

Sub-cooled liquid

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

Higher critical temperature

Tow specific heat of liquid

High latent heat of vaporisation

High boiling point

25. 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 combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

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

5 to 7 TR

0.1 to 0.3 TR

3 to 5 TR

1 to 3 TR

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

High, of the order of 25°

As low as possible (3 to 11°C)

Zero

Any value

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

Simple evaporative air cooling system

Simple air cooling system

All of these

Bootstrap air cooling system

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

Sub-cooled liquid region

Wet vapour region

None of these

Superheated vapour region

30. Formation of frost on evaporator in refrigerator

Is immaterial

Increases heat transfer rate

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Page 4 of 4

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

None of these

Less

Same

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

33. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid becomes solid

34. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

Much below critical pressure

35. 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

(C.O.P.)_P = (C.O.P.)_R + 2

(C.O.P.)_P = (C.O.P.)_R + 1

36. During heating and dehumidification process, dry bulb temperature

Remains constant

Increases

None of these

Decreases

37. 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 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

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

Expansion valve

Compressor

Condenser

Evaporator

39. 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

Equal to critical temperature

None of the above

40. 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

Refrigeration & Air-Conditioning Practice Set-2

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