Refrigeration & Air-Conditioning Practice Set-2

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. 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

Same

Less

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

Compressor

Evaporator

Condenser

Expansion valve

3. The higher temperature in vapour compression cycle occurs at

Compressor discharge

Evaporator

Receiver

Expansion valve

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

0.1 to 0.3 TR

1 to 3 TR

5 to 7 TR

3 to 5 TR

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

High pressure liquid refrigerant

Low pressure liquid and vapour refrigerant

None of these

Low pressure vapour refrigerant

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

Higher critical temperature

Tow specific heat of liquid

High boiling point

High latent heat of vaporisation

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

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

The moisture present in it begins to condense

None of the above

It is not affected by the moisture present in the air

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

Discharge pressure

Back pressure

Critical pressure

Suction pressure

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

Less

Same

None of these

10. Critical pressure of a liquid is the pressure

Above which liquid becomes solid

Above which liquid becomes gas

Above which liquid will remain liquid

Above which liquid becomes vapour

Page 2 of 4

11. During heating and dehumidification process, dry bulb temperature

Decreases

Remains constant

None of these

Increases

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

Sub-cooled liquid

Liquid

Saturated liquid

Wet vapour

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

Low weight per tonne of refrigeration

Higher coefficient of performance

High heat transfer rate

Low temperature at high altitudes

14. Condensing temperature in a refrigerator is the temperature

Of freezing zone

Of cooling medium

Of evaporator

At which refrigerant gas becomes liquid

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

Lithium bromide

R-12

Sulphur dioxide

Carbon dioxide

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

None of these

Wet vapour region

Superheated vapour region

Sub-cooled liquid region

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

Smaller/bigger depending on capacity

Equal

Bigger

Smaller

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

It is toxic to mucous membranes.

All of these

It requires large displacement per TR compared to fluoro carbons.

It reacts with copper and its alloys.

19. Vertical lines on pressure-enthalpy chart show constant

Pressure lines

Temperature lines

Entropy lines

Total heat lines

20. One ton of the refrigeration is

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

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

The standard unit used in refrigeration problems

Page 3 of 4

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

Ammonia

Carbon dioxide

Fluorine

Sulphur dioxide

22. 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

23. Highest pressure encountered in a refrigeration system should be

Much above critical pressure

Near critical pressure

Much below critical pressure

Critical pressure of refrigerant

24. 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)

Any value

High, of the order of 25°

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

Equal to critical temperature

Reduced to a value below its critical temperature

Increased to a value above its critical temperature

None of the above

26. The COP of a domestic refrigerator

Is more than 1

Depends upon the make

Is less than 1

Is equal to 1

27. Carbon dioxide is

All of these

Odourless

Colourless

Non-flammable

28. Formation of frost on evaporator in refrigerator

Results in loss of heat due to poor heat transfer

Is immaterial

Increases heat transfer rate

Can be avoided by proper design

29. A one tonne refrigerating machine means that

One tonne refrigerant is used

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

30. 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

Page 4 of 4

31. Reducing suction pressure in refrigeration cycle

Lowers compressor capacity because vapour is lighter

Lowers evaporation temperature

All of these

Increases power required per ton of refrigeration

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

Is higher than that of the entering air

Is lower than that of the entering air

None of the above

Can be lower or higher than that of the entering air

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

Ammonia vapour goes into solution

Ammonia vapour is driven out of solution

Weak solution mixes with strong solution

34. 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 + 2

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

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

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

Reduce

Increase

None of these

Equalize

36. The optimum effective temperature for human comfort is

Lower in winter than in summer

Higher in winter than in summer

Same in winter and summer

Not dependent on season

37. The lowest thermal diffusivity is of

Lead

Rubber

Aluminium

Iron

38. The dry bulb temperature during sensible heating of air

Remains constant

Increases

Decreases

None of these

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

Between the combustion chamber and the first heat exchanger

Between the first heat exchanger and the secondary compressor

Between the second heat exchanger and the cooling turbine

Between the secondary compressor and the second heat exchanger

40. 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

A refrigerant should have low latent heat

Pre-cooling and sub-cooling bf refrigerant are same

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