r1 Subject1 Temperature Pressure Heat Transfer

8/3/2019 r1 Subject1 Temperature Pressure Heat Transfer

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R1 Fundamentals of Refrigeration

#1 Temperature, Pressure, & Heat Transfer
http://../Refrigeration%20Main%20Topics.ppthttp://../Refrigeration%20Main%20Topics.ppthttp://../Refrigeration%20Subjects.ppthttp://../Refrigeration%20Subjects.ppthttp://../Refrigeration%20Subjects.ppthttp://../Refrigeration%20Subjects.ppthttp://../Refrigeration%20Main%20Topics.ppthttp://../Refrigeration%20Main%20Topics.ppt


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2004 Refrigeration Training Services - R1 Subject 1 Temperature,Pressure & Heat Transfer v1.2 2

Heat and Cold

Cold is the absence of heat.

Heat migrates to cold.

Insulation slows the transfer of heat, not stop it.


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Summer Heat Gain

95Heat flows from hot to cold

75Heat Transfer


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Winter Heat Loss

070Heat Transfer

Heat flows from hot to cold


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Heat Rises, Cold Falls

Warm air rises, cooler air falls.

In a multistory house;

the heat tends to rise upstairs, the cold falls downstairs.


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Summer in a 3-StoryTownhouse

9575

75

75Fan running


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Summer in a 3-StoryTownhouse

9575

75

75Fan running

80

Fan stops

75

70

C

oldairfalls



Winter in a 3-Story Townhouse

70

70

70Fan running

0



70

Winter in a 3-Story Townhouse

70

70

Fan running

70

75

Fan stops

70

68Ho

tairrises

0



Temperature measurementFahrenheitCelsius

212F

32F

100C

0C

Water boils

F = (9/5 x C) + 32

F = (1.8 x C) + 32

F = (1.8 x 100) + 32F = (180) + 32

F = 212

Water freezesConvert C to F:

C = .55 x (F 32)

C = .55 x (32 -32)

C = 0



Barometer

Atmospherepushesdown

29.92In. Hg

5

0

10

15

20

25

30

Inches

Mercury (Hg)



Elevation and boiling temperatures

29.9

At sea level water boils at 212 F

25.0

At 5000 elevation water boils at 203 F

At 30,000 elevation water boils at 100 F

1.0



Evacuation & Boiling Points

80

in. Hg Microns Boil Point

29.92 760,000 212F10.00 258,000 162F2.00 52,000 102F1.00 25,000 80F

.20 5,000 35F

.10 2,500 20F

.04 1,000 5F

.02 500 0F

.01 250 -3F

VacuumPump

5

10

15

20

25

30

In.Hg

DROP

Water Mercury



Pressure and Boiling Points

0 psig

At 0 psig water boils at 212

30 psig

At 30 psig water reaches 271 before boiling



Absolute (psia) vs. Barometric (In. Hg)

Atmospherepushesdown

0

5

10

15

20

25

30

In. Hg.

29.92In. Hg

2.5

5

7.5

10

12.5

15

PSI Absolute

14.7PSIA

0

Mercury (Hg)


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60

25

R-134a

R-22

R-404a


Low Side Gauge (Compound Gauge)

7.4 psia15 in. Hg0 psia

0 in. Hg

30 psig44.7 psia

0 psig14.7 psia

29.92 in. Hg



Low Side & High Side Gauges

Low Side (suction) gauge

Bluefor cold

Compound gauge Both positive pressure and vacuum

High Side (discharge) gauge

Redfor hot


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Pressure GaugesHigh SideLow Side

60

25

R-134a

R-22

R-404a

10R-134a

R-404a

R-22


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Low Side Gauge

Read suction pressure

Read suction temperature

Read vacuum


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60

25

R-134a

R-22

R-404a


Reading the Low Side Gauge

40 (R22)

69 psig49 psig

25 (R22)


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High Side Gauge

Read condensing pressure

Read condensing temperature

R di th Hi h Sid G


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10

R-134a

R-404a

R-22


Reading the High Side Gauge

125 (R22)

278 psig

210 psig

105 (R22)


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Pressure / Temperature (PT) Charts

From the system pressure

You can find its temperature

If you know the evaporator temperatureYou can find the suction pressure

If you know the condensing temperature

You can find the discharge pressure

Pressure Temperatures


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Pressure TemperaturesPSIG 22 404A404A134a134a 22

180 123 94 82185 125 96 84190 127 98 86

195 128 100 88200 130 101 89210 134 105 92220 137 108 95230 140 111 99240 143 114

250 146 117 104260 149 120 107

102

270 152 123 110280 155 126 113290 128 115300 131 118

325 137 124350 143 129375 149 134400 155 139425 144450 149

475 154

If the condensingtemperature is 125,

What is the headpressure of:

R134a

R22

R404A

185 psig

278 psig

333 psig

If the head pressureof R22 is 210 psig,

The condensingtemperature would be?

105

P T


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Pressure Temperature

PSIG 22 404A404A48 52 24 1449 53 25 1550 54 26 1652 56 28 1754 57 29 1956 58 31 2058 60 32 2260 62 34 23

62 63 3564 65 37 2666 66 38 27

25

68 68 40 29

70 69 41 30

134a134a 22 What is the suctionpressure if,

the evaporatortemperature is:

40 for R22 A/C

25 for R22 Walk-in

68 psig

49 psig

25 for R404 Walk-in62 psig

What is the evaporatortemperature of R404,

if the suctionpressure 50 psig? 16

U d t di L t t & S ibl H t


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Heat required to raise temperature or change state of a substance:

Weight X Specific heat X Temperature Difference = BTU

Understanding Latent & Sensible Heatby Heating Ice From 0F to Steam @ 212F

0

212

160 340 1310

32

16 BTUH 144 BTUH

Latent Heat of Fusion

180 BTUH 970 BTUH

Latent Heat of Vaporization

How much heat is required to raise 1lb. of ice 1F?

1lb. ice X .5 (Specific heat of ice) X 1F = .5 BTU

How much heat to raise 0F ice to 32F ice?

1lb. ice X .50 (specific heat of ice) X (32-0)F = 16 BTU

How much heat to change 1lb. of 32F ice to 32F water?

1lb. ice X 144 BTU = 144 BTU (Latent heat of fusion)

How much to raise 1# of water from 32F to 212F?

1lb. water X (212-32) = 180 BTU

How much to change 212F water to 212F steam?

1lb. water X 970 BTU = 970 BTU (Latent heat of vaporization)


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Refrigeration effect of ice

Ice melts by absorbing heat,

Cools surrounding air.

Ton of refrigeration =

Latent heat of Ton of ice =

2000 lbs. (ton) x 144 BTU (latent heat of ice) =

288,000 Btu (to melt a ton of ice in 24 hours) =12,000 Btu per hour.

U T b M t


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U-Tube Manometer

0123

456

123

456

5 WC

Air flow causespressure in the duct

Pressure moveswater column

Pressure is measured in inches of water column (WC)


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Three States of Substance

Abovefreezing

Boiling

Solids exert pressureon their base

Liquids exert pressure

on the surfaces oftheir container

Gases exert pressureequally in all directions

S


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Summary:Forces Exerted by Three States of a Substance

SOLID

LIQUID VAPOR


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Pascals LawPressure applied upon a confined fluid is

transmitted equally in all directions.

First used in the development ofhydraulic brakes.

Refrigerant is a pressurized confined fluid.

Whether liquid, vapor, or a combination thepressures are the same within its part of the

system.The high side of the system maintains thesame pressure throughout, as does the lowside.

LIQUIDVAPOR

D lt L


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Daltons Law

NitrogenOxygen Mixture of Oxygenand Nitrogen

The total pressure of a confined mixture of gases is the

sum of the pressures of each of the gasses in the mixture.

30 psig 40 psig 70 psig

D it


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Density

Wood Density 38 lb/ft3

Turtle Density of ???IRON

Water @ Density of 62 lb/ft3

Iron Ball Densityof 480 lb/ft3

Specific Gravity:The density of a substance

relative to the density of water.Water = 62 62 = 1.0

Wood = 38 62 = .6 (Floats)

Iron = 480 62 = 7.7 (Sinks)

S ifi H t


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Specific Heat

Specific Heat (SH):

The amount of heat (Btu) required to raise(or lower) 1 pound of a substance 1 F.

SH of water = 1

SH of ice = .5

How much heat is needed to raise 1 lb. water 1

Q = W x SH x TQ =1lb. x 1 x 1 = 1Btu

1 Btu raises 1 lb. of water 1 F.


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r1 Subject1 Temperature Pressure Heat Transfer