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refrigeration theory [finalized!] > [D2L] Midterm > Flashcards

[D2L] Midterm Flashcards

1
Q

The refrigerant in the center of the evaporator is in what state?

A

Saturated

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2
Q

What pressures do Refrigeration Gauges read? MULTI-SELECT (Select 2)

Inches of Mercury in a vacuum
Psia
Psig
Inches of water column
volume in cubic inches

A

Inches of Mercury in a vacuum
Psig

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3
Q

When a liquid is lowered beyond its boiling point while at the boiling pressure is called

A

Subcooling

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4
Q

1 micron =

A

0.001 millimeters

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5
Q

What order does refrigerant flow? (start with the compressor)

A
  1. Compressor
  2. Condenser
  3. Metering device
  4. Evaporator
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6
Q

All matter is composed of molecules that are in constant motion.

T or F

A

True

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7
Q

Which of the following statements is true?

1) An increase in work equals an decrease in heat.
2) A decrease in work equals a decrease in heat
3) A decrease in work equals an increase in heat

A

A decrease in work equals a decrease in heat

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8
Q

What two heat concepts affect refrigeration significantly?

A

Superheating vapours and subcooling liquids

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9
Q

What principle is needed between two objects in order to transfer heat?

A

There must be a temperature difference

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10
Q

Which method of heat transfer uses liquids and gases and involves fast vibrating molecules take up more space than slower vibrating molecules?

A

Convection

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11
Q

You finish brazing and decide to grab the pipe, what type of exciting heat transfer do you experience?

A

Conduction

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12
Q

Radiation can travel through space.

T or F

A

True

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13
Q

What kind of mechanical energy do we use to transfer from a low zone to a high zone?

1) Pumps
2) Compressors
3) Fans
4) All of the above

A

All of the above

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14
Q

What is a Btu?

A

The amount of heat required to raise the temperature of 1 lb of water by one Fahrenheit degree.

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15
Q

The unit for specific heat is Btu/lb./Fahrenheit degree

T or F

A

True

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16
Q

Latent heat is considered hidden heat because it does not register on a thermometer.

T or F

A

True

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17
Q

What is the freezing temperature for water?

1) 32F
2) 32C
3) 0C
4) Both A & C

A

Both A & C

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18
Q

What makes up the sum of total heat?

1) Sensible heat
2) Latent heat
3) Both

A

Both

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19
Q

What is dry bulb temperature?

A

the sensible temperature of the air determined with a dry thermometer

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20
Q

Which has the fastest moving molecules?

1) A hot cup of water
2) a cold cup of water
3) both hot and cold cups of water have the same rate of molecular motion

A

A hot cup of water

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21
Q

What will a vapour changing to a liquid do to heat?

A

Release heat

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22
Q

Specific heat is the amount of heat required to changed one pound of substance by one Fahrenheit degree.

T or F

A

True

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23
Q

kinetic energy is energy based on position

T or F

A

False

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24
Q

What is positive displacement?

A

The process of moving a piston to squeeze vapour in a cylinder

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25
Q

How does a centrifugal compressor increase refrigerant pressure?

A

Forces the acceleration of refrigerant

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26
Q

Where does the refrigerant change pressure? (MULTI-SELECT)

1) Metering device
2) Condenser
3) Compressor
4) Evaporator

A

1) Metering device
3) Compressor

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27
Q

What is the order of the state change that occurs in the condenser?

A
  1. Desuperheat
  2. Condensing
  3. Subcooling
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28
Q

What should the state of the refrigerant be at the outlet of the evaporator?

1) High pressure vapour
2) High pressure liquid
3) Low pressure liquid
4) Low pressure vapour

A

4) Low pressure vapour

29
Q

What is superheating?

A

The process of adding sensible heat to a vapour while it remains at a constant pressure.

30
Q

List the order of state the refrigerant is in the evaporator.

A
  1. Mostly liquid
  2. 1/2 liquid and 1/2 vapour
  3. Complete vapour
31
Q

Absolute zero is when molecular motion stops.

T or F

A

True

32
Q

What temperature is absolute zero?

A

0R

33
Q

Which law is the sum of each individual gas equals the total pressure?

A

Daltons law

34
Q

There are 4 gauges attached to this closed vapour filled system. What pressure will each gauge read? you see 200psi

A

200 psi each (Pascal’s Law)

35
Q

It’s a cold winters day, your journeyman tells you to grab a bottle of R22 from his van outside, to a 85F degree mechanical room, what will happen to the pressure inside the cylinder?

A

Increase

36
Q

What will happen to the pressure inside a cylinder with a pressure of 30 psig and a volume of 10 cubic inches, if the piston moves upstroke and reduces the volume to 2 cubic inches?

A

Increase

37
Q

What will cause the most turbulent flow?

1) Deburred pipe
2) Bends made with pipe benders
3) Short radius 90’s
4) Couplings

A

Short radius 90’s

38
Q

You are working on a boiler in the basement of a 100’ tall hotel, if the pressure gauge in the basement shows 40psi, how much pressure should you expect on the top floor?

A

0psi

39
Q

What is the velocity of the refrigerant flowing through the refrigeration system?

A

Mass flow rate

40
Q

What is the amount of heat added by the compressor and the compression process during the refrigeration cycle?

A

Heat of Compression

41
Q

What is the amount of heat gained in the evaporator during the refrigeration cycle?

A

Net Refrigeration Effect

42
Q

What is the amount of heat rejected by the condensing process?

A

Heat of Rejection

43
Q

Lower CoP (Coefficient of Performance) values result in an effective performance

T or F

A

False

44
Q

Lower CR (Compression Ratio) values result in a greater system performance

A

True

45
Q

You grab a bottle labelled r410a from a 65F room and hook up you gauges to it. It reads 185.1psig. What is in the bottle?

A

saturated refrigerant

46
Q

You grab a bottle labelled r134a from the 65F storage room and hook up your gauges. It reads 140.5psig. What is in the bottle?

A

unknown/contaminated mixture

47
Q

A change of state from a solid directly to a vapour without having a liquid state

A

Sublimation

48
Q

Convert 5psia to “hg

A

19.8 “hg

49
Q

Convert 150kpaa to psig

A

7.07

50
Q

Convert 460F to K

A

510K

51
Q

Its a cold -40F day. you take a big birthday balloon from your car at -40F to inside at 70F, and it started at 4 cuft, what should the current volume of the balloon be?

A

5 cuft

52
Q

How much heat would be required to turn 1 lbs of 40F water into 412F steam @ 0.46

A

1234

53
Q

a compressed gas cylinder of 3cu/ft is filled to 150psig. Trent dropped the bottle from the building and dented it, reducing the volume to 2cu/ft. as the ambient temperature has remained constant, what is the new pressure in the bottle?

A

232psig

54
Q

Fluid pressure based on the height of a column of liquid

A

Static/Head Pressure

55
Q

Your boss can’t figure out what’s wrong with a cooler so he’s asked you to plot the system out on a PE chart for him. Plot the system below on a PE chart (provided) so your boss can figure out what’s wrong

Use the 134a PE Chart

SDT 140F

SST 20F

Superheat 60F

Subcooling 20F

What is H1 in Btu/Lbs? (H1 = TXV inlet)

(Answer to nearest whole number, no decimals, no units) Example: 74

A

Answer: 40

56
Q

Use the 134a PE Chart

SDT 140F

SST 20F

Superheat 60F

Subcooling 20F

What is H2 in Btu/Lbs? (H2 = TXV outlet)

(Answer to nearest whole number, no decimals, no units)

A

Answer: 40

57
Q

Use the 134a PE Chart

SDT 140F

SST 20F

Superheat 60F

Subcooling 20F

What is H3/H4 in Btu/Lbs? (H3 = Outlet of compressor, H4 = inlet of compressor, for this they are the same number)

(Answer to nearest whole number, no decimals, no units)

A

Answer: 110

58
Q

Use the 134a PE Chart

SDT 140F

SST 20F

Superheat 60F

Subcooling 20F

What is H5 in Btu/Lbs? (H5 = Outlet of Compressor)

(Answer to nearest whole number, no decimals, no units)

A

Answer: 130

59
Q

On a PE chart what component is on the far left?

A

TXV

60
Q

If you increase subcooling will it increase your NRE?

A

Yes

61
Q

Hooking up your gauges to the 134a system, you read 30psi and 230psi. What is the Compression ratio?

A

5.47:1

62
Q

Which type of compressor is a non-positive displacement compressor?

A

Centrifugal

63
Q

SST = 35F

SDT = 100F

Evap Supply temp = 50F

Evap Return temp = 70F

Condenser Supply Temp = 125F

Condenser Return Temp = 95F

What is the Temp Drop for this system?

A

20F

64
Q

What type of compressor did we take apart in class?

A

Semi-hermetic

65
Q

Energy travels from High energy position to Low energy position, AKA: Heat travels from Hot to Cold

T or F

A

True

66
Q

Leaving the metering device, what state is the refrigerant in?

A

80% Liquid, 20% Vapour

67
Q

You are working on a cooler and find the evaporator fan has died. What should you be worried about? (Hint: Evaporators fans push warm air across a colder coil)

A

Too little superheat

68
Q

You show up to a service call and the unit has tripped on high head pressure. What could the issue be? (MULTI-SELECT) (SELECT 6 of the Answers)

Undercharge (Low on refrigerant)

Overcharge (too much refrigerant)

Restricted/Dirty condenser

Restricted/Dirty Evaporator

Heavy Load (high return air temp)

Light Load (low return air temp)

Non-condensables in the system (moisture/bad gas in the system)

Low outdoor ambient

High outdoor ambient

Dead condenser fan motor

Dead evaporator fan motor

A

Overcharge (too much refrigerant)
Restricted/Dirty condenser
Non-condensables in the system (moisture/bad gas in the system)
High outdoor ambient
Dead condenser fan motor
Heavy Load (high return air temp)

refrigeration theory [finalized!] (20 decks)

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