Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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

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 pressure at the inlet of a refrigerant compressor is called

Discharge pressure

Critical pressure

Back pressure

Suction pressure

4. 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

5. Carbon dioxide is

Colourless

Non-flammable

All of these

Odourless

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

None of the above

Equal to critical temperature

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

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

Equal

Bigger

Smaller/bigger depending on capacity

Smaller

8. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

Of evaporator

At which refrigerant gas becomes liquid

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

Compressor

Evaporator

Condenser

Expansion valve

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

Low temperature at high altitudes

Higher coefficient of performance

Low weight per tonne of refrigeration

High heat transfer rate

Page 2 of 4

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

Reduce

Increase

None of these

Equalize

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

Same

Less

More

More/less depending on rating

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

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

Ammonia vapour goes into solution

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

Zero

As low as possible (3 to 11°C)

High, of the order of 25°

Any value

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

5 to 7 TR

0.1 to 0.3 TR

1 to 3 TR

3 to 5 TR

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

Simple evaporative air cooling system

Bootstrap air cooling system

All of these

Simple air cooling system

17. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

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

It is not affected by the moisture present in the air

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

The moisture present in it begins to condense

None of the above

19. Choose the correct statement

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

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

20. A one tonne refrigerating machine means that

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 of water can be converted into ice

One tonne refrigerant is used

One tonne is the total mass of machine

Page 3 of 4

21. During heating and dehumidification process, dry bulb temperature

None of these

Remains constant

Decreases

Increases

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

R-12

Sulphur dioxide

Lithium bromide

Carbon dioxide

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

Sub-cooled liquid

Saturated liquid

Wet vapour

Liquid

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

Sulphur dioxide

Fluorine

Carbon dioxide

Ammonia

25. The lowest thermal diffusivity is of

Rubber

Iron

Lead

Aluminium

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

Is higher than that of the entering air

Can be lower or higher than that of the entering air

Is lower than that of the entering air

None of the above

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

Superheated vapour region

None of these

Wet vapour region

Sub-cooled liquid region

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

High latent heat of vaporisation

Higher critical temperature

Tow specific heat of liquid

High boiling point

29. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

30. One ton of the refrigeration is

The standard unit used in refrigeration problems

The cooling effect produced by melting 1 ton of ice

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

Page 4 of 4

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

After passing through the condenser

Before entering the expansion valve

Before passing through the condenser

After passing through the expansion or throttle valve

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

High pressure liquid refrigerant

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

None of these

33. The COP of a domestic refrigerator

Is more than 1

Is less than 1

Depends upon the make

Is equal to 1

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

It is toxic to mucous membranes.

All of these

It reacts with copper and its alloys.

It requires large displacement per TR compared to fluoro carbons.

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

None of these

Same

More

Less

37. 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

38. Highest pressure encountered in a refrigeration system should be

Near critical pressure

Much above critical pressure

Critical pressure of refrigerant

Much below critical pressure

39. The dry bulb temperature during sensible heating of air

None of these

Increases

Remains constant

Decreases

40. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

Refrigeration & Air-Conditioning Practice Set-2

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