Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

2. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Is immaterial

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

All of these

Simple evaporative air cooling system

Simple air cooling system

Bootstrap air cooling system

4. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

Not dependent on season

5. 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

6. During heating and dehumidification process, dry bulb temperature

Increases

Decreases

None of these

Remains constant

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

More

More/less depending on rating

Less

Same

8. 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

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

Higher critical temperature

High boiling point

High latent heat of vaporisation

Tow specific heat of liquid

10. 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 cooling effect produced by melting 1 ton of ice

The standard unit used in refrigeration problems

Page 2 of 4

11. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Pressure lines

Entropy lines

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

Sub-cooled liquid region

Wet vapour region

Superheated vapour region

None of these

13. The lowest thermal diffusivity is of

Aluminium

Rubber

Iron

Lead

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

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

The moisture present in it begins to condense

It is not affected by the moisture present in the air

None of the above

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

3 to 5 TR

1 to 3 TR

5 to 7 TR

0.1 to 0.3 TR

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

High heat transfer rate

Low temperature at high altitudes

Higher coefficient of performance

Low weight per tonne of refrigeration

17. 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

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

Equal

Smaller

Bigger

Smaller/bigger depending on capacity

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

None of these

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

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

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

All of these

It is toxic to mucous membranes.

Page 3 of 4

21. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid will remain liquid

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

Carbon dioxide

Sulphur dioxide

Fluorine

Ammonia

23. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Depends upon the make

Is equal to 1

24. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Much above critical pressure

Near critical pressure

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

More

Same

None of these

Less

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

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

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

Critical pressure

Suction pressure

Discharge pressure

Back pressure

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

Liquid

Sub-cooled liquid

Saturated liquid

Wet vapour

29. 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°

30. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Receiver

Evaporator

Page 4 of 4

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

Condenser

Evaporator

Compressor

Expansion valve

32. The dry bulb temperature during sensible heating of air

None of these

Remains constant

Decreases

Increases

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

R-12

Carbon dioxide

Lithium bromide

Sulphur dioxide

34. 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

35. Carbon dioxide is

Non-flammable

Colourless

Odourless

All of these

36. 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 + 1

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

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

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

Equal to critical temperature

None of the above

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

38. Condensing temperature in a refrigerator is the temperature

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

Of evaporator

39. A one tonne refrigerating machine means that

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

One tonne is the total mass of machine

One tonne of water can be converted into ice

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

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

Refrigeration & Air-Conditioning Practice Set-2

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