Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

2. 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

Is higher than that of the entering air

None of the above

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

Back pressure

Critical pressure

Discharge pressure

Suction pressure

4. The COP of a domestic refrigerator

Is less than 1

Is more than 1

Depends upon the make

Is equal to 1

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

Sulphur dioxide

Fluorine

Carbon dioxide

Ammonia

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

Saturated liquid

Wet vapour

Liquid

Sub-cooled liquid

7. 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 - 1

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

8. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

9. 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

10. Critical pressure of a liquid is the pressure

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes vapour

Page 2 of 4

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

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

After passing through the condenser

12. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

13. 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

Same

More

Less

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

Carbon dioxide

Sulphur dioxide

Lithium bromide

R-12

15. 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

16. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

17. The higher temperature in vapour compression cycle occurs at

Receiver

Compressor discharge

Evaporator

Expansion valve

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

Compressor

Expansion valve

Evaporator

Condenser

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

0.1 to 0.3 TR

3 to 5 TR

5 to 7 TR

1 to 3 TR

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

Bootstrap air cooling system

Simple air cooling system

Simple evaporative air cooling system

All of these

Page 3 of 4

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

Same

Less

More

None of these

22. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

23. One ton of the refrigeration is

The standard unit used in refrigeration problems

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

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

It is not affected by the moisture present in the air

None of the above

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

The moisture present in it begins to condense

25. 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.

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

Sub-cooled liquid region

None of these

Wet vapour region

Superheated vapour region

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

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

Low pressure vapour refrigerant

28. Carbon dioxide is

Non-flammable

All of these

Colourless

Odourless

29. 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

30. 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

Page 4 of 4

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

High heat transfer rate

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

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

Increased to a value above its critical temperature

Equal to critical temperature

Reduced to a value below its critical temperature

None of the above

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

Tow specific heat of liquid

High latent heat of vaporisation

Higher critical temperature

High boiling point

34. The optimum effective temperature for human comfort is

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

Same in winter and summer

35. The lowest thermal diffusivity is of

Lead

Aluminium

Iron

Rubber

36. 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

37. 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

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

High, of the order of 25°

Zero

As low as possible (3 to 11°C)

Any value

39. A one tonne refrigerating machine means that

One tonne is the total mass of machine

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

One tonne of water can be converted into ice

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

Equal

Smaller

Bigger

Smaller/bigger depending on capacity

Refrigeration & Air-Conditioning Practice Set-2

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