Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

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

Smaller/bigger depending on capacity

Bigger

Smaller

Equal

2. 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

3. 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

None of the above

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

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

Back pressure

Critical pressure

Discharge pressure

Suction pressure

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

Before passing through the condenser

After passing through the condenser

After passing through the expansion or throttle valve

Before entering the expansion valve

6. One ton of the refrigeration is

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

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

The cooling effect produced by melting 1 ton of ice

7. Condensing temperature in a refrigerator is the temperature

At which refrigerant gas becomes liquid

Of evaporator

Of freezing zone

Of cooling medium

8. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid will remain liquid

Above which liquid becomes vapour

Above which liquid becomes gas

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

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

Between the combustion chamber and the first heat exchanger

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

Wet vapour region

Sub-cooled liquid region

Superheated vapour region

None of these

Page 2 of 4

11. The dry bulb temperature during sensible heating of air

Decreases

Increases

Remains constant

None of these

12. During heating and dehumidification process, dry bulb temperature

None of these

Decreases

Remains constant

Increases

13. 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 refrigerant is used

One tonne is the total mass of machine

One tonne of water can be converted into ice

14. The higher temperature in vapour compression cycle occurs at

Receiver

Compressor discharge

Expansion valve

Evaporator

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

Less

Same

None of these

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

Saturated liquid

Liquid

Sub-cooled liquid

Wet vapour

17. 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.

18. 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

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

Sulphur dioxide

Carbon dioxide

Lithium bromide

R-12

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

Increased to a value above its critical temperature

Reduced to a value below its critical temperature

None of the above

Equal to critical temperature

Page 3 of 4

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

Sulphur dioxide

Carbon dioxide

Fluorine

Ammonia

22. The optimum effective temperature for human comfort is

Not dependent on season

Same in winter and summer

Higher in winter than in summer

Lower in winter than in summer

23. The COP of a domestic refrigerator

Is more than 1

Is equal to 1

Is less than 1

Depends upon the make

24. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Increases heat transfer rate

Is immaterial

Can be avoided by proper design

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

Simple evaporative air cooling system

All of these

Bootstrap air cooling system

Simple air cooling system

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

Low pressure vapour refrigerant

None of these

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

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

Low weight per tonne of refrigeration

Higher coefficient of performance

Low temperature at high altitudes

High heat transfer rate

28. 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

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

1 to 3 TR

3 to 5 TR

0.1 to 0.3 TR

5 to 7 TR

30. 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

Page 4 of 4

31. Carbon dioxide is

Odourless

Non-flammable

All of these

Colourless

32. 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

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

Compressor

Expansion valve

Condenser

Evaporator

34. Vertical lines on pressure-enthalpy chart show constant

Total heat lines

Temperature lines

Entropy lines

Pressure lines

35. 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

36. 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 higher than that of the entering air

Is lower than that of the entering air

37. The lowest thermal diffusivity is of

Aluminium

Lead

Iron

Rubber

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

Less

More/less depending on rating

Same

39. Highest pressure encountered in a refrigeration system should be

Critical pressure of refrigerant

Much below critical pressure

Near critical pressure

Much above critical pressure

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

High, of the order of 25°

Zero

As low as possible (3 to 11°C)

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