Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

None of these

Less

More

Same

2. A one tonne refrigerating machine means that

One tonne of water can be converted into ice

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

3. The dry bulb temperature during sensible heating of air

Decreases

Increases

Remains constant

None of these

4. The COP of a domestic refrigerator

Is equal to 1

Depends upon the make

Is more than 1

Is less than 1

5. 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

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

Evaporator

Expansion valve

Condenser

Compressor

7. Critical pressure of a liquid is the pressure

Above which liquid becomes vapour

Above which liquid will remain liquid

Above which liquid becomes gas

Above which liquid becomes solid

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

Increase

Equalize

Reduce

None of these

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

None of the above

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

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

Higher coefficient of performance

High heat transfer rate

Low weight per tonne of refrigeration

Low temperature at high altitudes

Page 2 of 4

11. The higher temperature in vapour compression cycle occurs at

Expansion valve

Evaporator

Compressor discharge

Receiver

12. 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

13. During heating and dehumidification process, dry bulb temperature

Decreases

Increases

None of these

Remains constant

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

Low pressure liquid and vapour refrigerant

None of these

High pressure liquid refrigerant

Low pressure vapour refrigerant

15. Carbon dioxide is

Odourless

Non-flammable

Colourless

All of these

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

Ammonia

Fluorine

Carbon dioxide

Sulphur dioxide

17. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Much above critical pressure

Near critical pressure

Critical pressure of refrigerant

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

Sub-cooled liquid

Wet vapour

Saturated liquid

Liquid

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

Lithium bromide

Sulphur dioxide

R-12

Carbon dioxide

20. 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

Less

More

Same

Page 3 of 4

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

Sub-cooled liquid region

Wet vapour region

None of these

Superheated vapour region

22. 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.

It requires large displacement per TR compared to fluoro carbons.

All of these

23. The optimum effective temperature for human comfort is

Same in winter and summer

Lower in winter than in summer

Not dependent on season

Higher in winter than in summer

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

Smaller/bigger depending on capacity

Equal

Smaller

Bigger

25. The lowest thermal diffusivity is of

Lead

Aluminium

Iron

Rubber

26. 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 + 2

(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

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

Between the combustion chamber and the first heat exchanger

Between the secondary compressor and the second heat exchanger

Between the second heat exchanger and the cooling turbine

Between the first heat exchanger and the secondary compressor

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

After passing through the expansion or throttle valve

Before passing through the condenser

Before entering the expansion valve

After passing through the condenser

29. 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

Pre-cooling and sub-cooling bf refrigerant are same

A refrigerant should have low latent heat

30. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Entropy lines

Total heat lines

Pressure lines

Page 4 of 4

31. 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

32. 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

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

0.1 to 0.3 TR

5 to 7 TR

1 to 3 TR

3 to 5 TR

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

None of the above

Reduced to a value below its critical temperature

Equal to critical temperature

Increased to a value above its critical temperature

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

Back pressure

Discharge pressure

Critical pressure

Suction pressure

36. Reducing suction pressure in refrigeration cycle

Increases power required per ton of refrigeration

Lowers evaporation temperature

All of these

Lowers compressor capacity because vapour is lighter

37. One ton of the refrigeration is

The cooling effect produced by melting 1 ton of ice

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

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

38. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Results in loss of heat due to poor heat transfer

Can be avoided by proper design

Is immaterial

39. Condensing temperature in a refrigerator is the temperature

Of freezing zone

At which refrigerant gas becomes liquid

Of evaporator

Of cooling medium

40. 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

Refrigeration & Air-Conditioning Practice Set-2

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection

Refrigeration & Air-Conditioning Practice Set-2

Share this Now with Friends:

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection