Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of cooling medium

Of evaporator

2. Reducing suction pressure in refrigeration cycle

All of these

Increases power required per ton of refrigeration

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

3. The lowest thermal diffusivity is of

Rubber

Lead

Aluminium

Iron

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

High boiling point

High latent heat of vaporisation

Higher critical temperature

Tow specific heat of liquid

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

Any value

As low as possible (3 to 11°C)

Zero

High, of the order of 25°

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

Compressor

Condenser

Evaporator

Expansion valve

7. 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

Less

More

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

3 to 5 TR

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

9. Choose the correct statement

Superheat and sensible heat of a refrigerant are same

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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

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

Less

More

None of these

Same

Page 2 of 4

11. 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

12. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

13. 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

Weak solution mixes with strong solution

14. 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

15. 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.

All of these

It reacts with copper and its alloys.

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

Fluorine

Sulphur dioxide

Carbon dioxide

Ammonia

17. The optimum effective temperature for human comfort is

Same in winter and summer

Higher in winter than in summer

Not dependent on season

Lower in winter than in summer

18. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

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

Smaller

Bigger

Equal

Smaller/bigger depending on capacity

20. 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

Page 3 of 4

21. 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

22. 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

None of the above

The moisture present in it begins to condense

It is not affected by the moisture present in the air

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

Higher coefficient of performance

Low weight per tonne of refrigeration

Low temperature at high altitudes

High heat transfer rate

24. 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

25. A one tonne refrigerating machine means that

One tonne refrigerant is used

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

26. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

27. The dry bulb temperature during sensible heating of air

None of these

Increases

Decreases

Remains constant

28. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Temperature lines

Total heat lines

Entropy lines

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

Wet vapour

Liquid

Sub-cooled liquid

Saturated liquid

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

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

Before passing through the condenser

Page 4 of 4

31. 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

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

33. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Evaporator

Receiver

Expansion valve

34. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

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 refrigeration effect to produce 1 ton of ice at NTP conditions

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

None of these

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

High pressure liquid refrigerant

36. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes solid

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

Sulphur dioxide

Carbon dioxide

R-12

Lithium bromide

38. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

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

Equal to critical temperature

Increased to a value above its critical temperature

None of the above

Reduced to a value below its critical temperature

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

Simple air cooling system

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

Refrigeration & Air-Conditioning Practice Set-2

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