Refrigeration & Air-Conditioning Practice Set-2

Page 1 of 4

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

Can be lower or higher than that of the entering air

None of the above

Is lower than that of the entering air

Is higher than that of the entering air

2. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Receiver

Evaporator

Expansion valve

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

High heat transfer rate

Low weight per tonne of refrigeration

Low temperature at high altitudes

Higher coefficient of performance

4. 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

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

It reacts with copper and its alloys.

All of these

It is toxic to mucous membranes.

It requires large displacement per TR compared to fluoro carbons.

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

Evaporator

Compressor

Condenser

Expansion valve

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

None of these

Low pressure vapour refrigerant

Low pressure liquid and vapour refrigerant

High pressure liquid refrigerant

8. 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

(C.O.P)_P = (C.O.P)_R - 1

(C.O.P.)_P = (C.O.P.)_R + 1

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

1 to 3 TR

5 to 7 TR

3 to 5 TR

0.1 to 0.3 TR

10. 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 standard unit used in refrigeration problems

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

The cooling effect produced by melting 1 ton of ice

Page 2 of 4

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

Bigger

Smaller

Equal

Smaller/bigger depending on capacity

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 pressure at the inlet of a refrigerant compressor is called

Discharge pressure

Critical pressure

Suction pressure

Back pressure

14. A one tonne refrigerating machine means that

One tonne is the total mass of machine

One tonne refrigerant is used

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

15. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is equal to 1

Is less than 1

16. 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

17. 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

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

The moisture present in it begins to condense

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

None of the above

19. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Can be avoided by proper design

Increases heat transfer rate

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

Equalize

None of these

Reduce

Increase

Page 3 of 4

21. During heating and dehumidification process, dry bulb temperature

None of these

Increases

Remains constant

Decreases

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

Higher critical temperature

Tow specific heat of liquid

High latent heat of vaporisation

High boiling point

23. Reducing suction pressure in refrigeration cycle

Lowers evaporation temperature

Lowers compressor capacity because vapour is lighter

All of these

Increases power required per ton of refrigeration

24. Critical pressure of a liquid is the pressure

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

Above which liquid becomes solid

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

Ammonia

Fluorine

Carbon dioxide

Sulphur dioxide

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

Simple evaporative air cooling system

Bootstrap air cooling system

Simple air cooling system

All of these

27. The optimum effective temperature for human comfort is

Not dependent on season

Higher in winter than in summer

Same in winter and summer

Lower in winter than in summer

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

Between the second heat exchanger and the cooling turbine

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

29. Condensing temperature in a refrigerator is the temperature

Of evaporator

Of cooling medium

At which refrigerant gas becomes liquid

Of freezing zone

30. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Pressure lines

Entropy lines

Temperature lines

Page 4 of 4

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

As low as possible (3 to 11°C)

Any value

Zero

High, of the order of 25°

32. 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

33. The dry bulb temperature during sensible heating of air

Increases

Remains constant

Decreases

None of these

34. The lowest thermal diffusivity is of

Rubber

Aluminium

Lead

Iron

35. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

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

Same

More

None of these

Less

37. Carbon dioxide is

Colourless

All of these

Odourless

Non-flammable

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

Liquid

Sub-cooled liquid

Wet vapour

Saturated liquid

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

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

None of these

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

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

Equal to critical temperature

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