Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. 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 first heat exchanger and the secondary compressor

Between the secondary compressor and the second heat exchanger

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

Reduced to a value below its critical temperature

None of the above

Increased to a value above its critical temperature

Equal to critical temperature

3. Formation of frost on evaporator in refrigerator

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

4. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

5. Carbon dioxide is

Non-flammable

Odourless

Colourless

All of these

6. 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

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

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

The moisture present in it begins to condense

8. The dry bulb temperature during sensible heating of air

None of these

Decreases

Remains constant

Increases

9. 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

10. 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

Superheat and sensible heat of a refrigerant are same

Pre-cooling and sub-cooling bf refrigerant are same

Page 2 of 4

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

Condenser

Evaporator

Expansion valve

Compressor

12. The COP of a domestic refrigerator

Is equal to 1

Is more than 1

Is less than 1

Depends upon the make

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

Low temperature at high altitudes

Higher coefficient of performance

High heat transfer rate

Low weight per tonne of refrigeration

14. 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

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

Wet vapour region

Sub-cooled liquid region

None of these

Superheated vapour region

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

Ammonia vapour goes into solution

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

Low pressure vapour refrigerant

None of these

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

More

Same

More/less depending on rating

Less

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

Bigger

Smaller/bigger depending on capacity

Equal

Smaller

20. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

Page 3 of 4

21. During heating and dehumidification process, dry bulb temperature

Remains constant

Decreases

Increases

None of these

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

Reduce

Equalize

Increase

None of these

23. 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

(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 + 2

24. 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

25. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes solid

Above which liquid becomes gas

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

Before entering the expansion valve

After passing through the expansion or throttle valve

Before passing through the condenser

After passing through the condenser

27. The higher temperature in vapour compression cycle occurs at

Evaporator

Expansion valve

Compressor discharge

Receiver

28. Vertical lines on pressure-enthalpy chart show constant

Entropy lines

Total heat lines

Temperature lines

Pressure lines

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

Sulphur dioxide

R-12

Carbon dioxide

Lithium bromide

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

Critical pressure

Back pressure

Suction pressure

Discharge pressure

Page 4 of 4

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

None of these

More

Less

Same

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

Is lower than that of the entering air

Is higher than that of the entering air

None of the above

Can be lower or higher than that of the entering air

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

Wet vapour

Liquid

Sub-cooled liquid

Saturated liquid

34. Reducing suction pressure in refrigeration cycle

All of these

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

35. 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 standard unit used in refrigeration problems

The refrigeration effect to produce 1 ton of ice at NTP conditions

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

Fluorine

Carbon dioxide

Sulphur dioxide

Ammonia

37. The lowest thermal diffusivity is of

Aluminium

Rubber

Lead

Iron

38. The optimum effective temperature for human comfort is

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

Not dependent on season

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

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

All of these

40. 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

Refrigeration & Air-Conditioning Practice Set-2

Related

Leave a ReplyCancel reply

Secured Payments

Protection

Refrigeration & Air-Conditioning Practice Set-2

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Secured Payments

Protection