Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

1. Choose the correct statement

A refrigerant should have low latent heat

Superheat and sensible heat of a refrigerant are same

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

2. The optimum effective temperature for human comfort is

Higher in winter than in summer

Not dependent on season

Lower in winter than in summer

Same in winter and summer

3. Reducing suction pressure in refrigeration cycle

All of these

Lowers evaporation temperature

Increases power required per ton of refrigeration

Lowers compressor capacity because vapour is lighter

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

Expansion valve

Condenser

Compressor

Evaporator

5. 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

6. 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

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

Less

Same

None of these

More

8. Highest pressure encountered in a refrigeration system should be

Much below critical pressure

Near critical pressure

Critical pressure of refrigerant

Much above critical pressure

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

3 to 5 TR

0.1 to 0.3 TR

5 to 7 TR

1 to 3 TR

10. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

Page 2 of 4

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

Bigger

Equal

Smaller/bigger depending on capacity

Smaller

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

Higher coefficient of performance

Low temperature at high altitudes

Low weight per tonne of refrigeration

High heat transfer rate

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

Same

More/less depending on rating

More

Less

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

Before passing through the condenser

After passing through the condenser

Before entering the expansion valve

After passing through the expansion or throttle valve

15. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

16. Carbon dioxide is

Non-flammable

All of these

Odourless

Colourless

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

Liquid

Saturated liquid

Wet vapour

Sub-cooled liquid

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

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

Between the combustion chamber and the first heat exchanger

19. 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.

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

Tow specific heat of liquid

High boiling point

Higher critical temperature

High latent heat of vaporisation

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

Superheated vapour region

None of these

22. The dry bulb temperature during sensible heating of air

None of these

Decreases

Remains constant

Increases

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

Equal to critical temperature

None of the above

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

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

Any value

Zero

High, of the order of 25°

As low as possible (3 to 11°C)

25. 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

26. 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

27. The lowest thermal diffusivity is of

Rubber

Aluminium

Iron

Lead

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

Carbon dioxide

Ammonia

Fluorine

Sulphur dioxide

29. The higher temperature in vapour compression cycle occurs at

Expansion valve

Compressor discharge

Evaporator

Receiver

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

Weak solution mixes with strong solution

Ammonia vapour is driven out of solution

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Page 4 of 4

31. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of evaporator

At which refrigerant gas becomes liquid

Of cooling medium

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

Is lower than that of the entering air

Can be lower or higher than that of the entering air

None of the above

Is higher than that of the entering air

33. Vertical lines on pressure-enthalpy chart show constant

Temperature lines

Total heat lines

Pressure lines

Entropy lines

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

Suction pressure

Discharge pressure

Critical pressure

Back pressure

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

All of these

Simple evaporative air cooling system

Simple air cooling system

Bootstrap air cooling system

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

Increase

Reduce

None of these

Equalize

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

Low pressure vapour refrigerant

None of these

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

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

The moisture present in it begins to condense

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

It is not affected by the moisture present in the air

None of the above

39. Formation of frost on evaporator in refrigerator

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

Results in loss of heat due to poor heat transfer

40. One ton of the refrigeration is

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

The standard unit used in refrigeration problems

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

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