Thermodynamics

ThermodynamicsThermodynamics

Laws & PropertiesLaws & Properties

Temperature & Pressure Temperature & Pressure ScalesScales

Thermodynamic CyclesThermodynamic Cycles

ThermodynamicsThermodynamicsBranch of science dealing with the Branch of science dealing with the

interchange of thermal & interchange of thermal & mechanical energymechanical energy

2 2 LawsLaws 6 6 PropertiesProperties 3 3 PhasesPhases 3 3 ModesModes of Heat Transfer of Heat Transfer 2 2 EffectsEffects of Heat Transfer of Heat Transfer

Thermodynamic LawsThermodynamic Laws 11stst Law: Law: Conservation of EnergyConservation of Energy(you can’t win—the best you can do is tie)

HEATIN

WORKOU

T

WORKIN

HEATOUT

SYSTEM

with stored, internal energy

U

HEATIN – HEATOUT = WORKOUT – WORKIN + U

The 1The 1stst Law is an accounting rule Law is an accounting rule

HHinin HHoutout HHnetnet WWoutout WWinin WWnetnet UU

6060 2020 4040 7575 5050 2525 1515

4040 8080 -40-40 100100 4040 6060 -20-20

200200 5050 150150 450450 300300 150150 00

00 150150 -150-150 00 150150 -150-150 00

9090 00 9090 9090 00 9090 00

1 BTU = 778 lb-ft = 1055 joules = 252 calories1 BTU = 778 lb-ft = 1055 joules = 252 calories

Thermodynamic LawsThermodynamic Laws 22stst Law: Law: Not all processes are reversibleNot all processes are reversible

(sometimes you can’t even tie)

HEATIN

WORKOU

T

WORKIN

HEATOUT

SYSTEM

with stored, internal energy

U

HEATOUT = WORKIN (can happen)

HEATIN = WORKOUT (cannot happen)


2 2 LawsLaws6 6 PropertiesProperties3 3 PhasesPhases3 3 ModesModes of Heat Transfer of Heat Transfer2 2 EffectsEffects of Heat of Heat

TransferTransfer

Thermodynamic Thermodynamic PropertiesProperties

Define the “state” of a systemDefine the “state” of a system

TemperatureTemperature, , TT ( (ooF, F, ooC, C, ooR, R, ooK)K)

PressurePressure, , PP (psi, bar, in. Hg) (psi, bar, in. Hg) Internal EnergyInternal Energy, , uu (BTU/lb) (BTU/lb) Specific VolumeSpecific Volume, , vv (cu.in./lb) (cu.in./lb) EnthalpyEnthalpy, , hh (BTU/lb) (BTU/lb) EntropyEntropy, , ss (BTU/lb) (BTU/lb)

P

Thermodynamic Thermodynamic PropertiesProperties

T PTPT

6 properties linked—measure any two 6 properties linked—measure any two calculate (or look up) other 4 calculate (or look up) other 4

Which two are you probably Which two are you probably going to observe (measure)?going to observe (measure)?

Temperature ScalesTemperature Scales Relative scales:Relative scales: Fahrenheit Fahrenheit && Celsius Celsius Absolute scales:Absolute scales: RankineRankine & & KelvinKelvin

494 oF

212 oF

98.6 oF72 oF32 oF0 oF

Freezing

Room Temp

Boiling (Atmos)

Body Temp

TSES Boiler

961 oR

672 oR

492 oR

0 oR

257 oC

100 oC

37 oC22 oC

0 oC

530 oK

373 ok

273 oK

0 oK Absolute Zero-460 oF -273 oC

180o 100o

Pressure ScalesPressure Scales Relative scales:Relative scales: psig, inches (Hg) of Vacuumpsig, inches (Hg) of Vacuum

14.7 psiAStandard

Atmosphere

TSES Boiler

Perfect Vacuum

29.92 “Hg0 “Hg

0 psiA 0 “Hg29.92 “Hg

614.7 psiA 600 psig

“gage pressure”

“inches of vacuum”

Vacuum measureVacuum measure

29.92 “Hg

Perfect Vacuum

Atmospheric Pressure A Barometer is used to measure

atmospheric pressure via comparison to a (very nearly) perfect vacuum

Vacuum measureVacuum measure

29.92 “HgAtmospheric Pressure

0 psia

20.0 “Hg

10.0 “Hg

0.0 “Hg

5 psia10 psia14.7 psia

A Vacuum Gage is used to measure the pressure in an evacuated space via comparison to atmospheric pressure

Evacuated Space



TransferTransfer

3 Phases of matter3 Phases of matterSolid Solid – – maintains shapemaintains shapeLiquid Liquid – – lower surface & sides lower surface & sides

conform to shape of container; conform to shape of container; upper surface flat & horizontalupper surface flat & horizontal

Vapor (Gas) – Vapor (Gas) – conforms to conforms to shape of containershape of container

A A FluidFluid is either a liquid or vapor is either a liquid or vapor which flows and can be pumpedwhich flows and can be pumped



TransferTransfer

3 Modes of heat 3 Modes of heat transfertransfer RadiationRadiation– – transfer through space transfer through space

viavia electromagnetic waves; travel in a electromagnetic waves; travel in a straight line (may reflect off surfaces)straight line (may reflect off surfaces)

ConductionConduction– – transfer through transfer through solids (molecule vibration)solids (molecule vibration)

ConvectionConvection– – transfer via transfer via movement of a fluidmovement of a fluid

NoteNote: : HeatHeat is thermal energy in is thermal energy in transition from a high temperature transition from a high temperature area to a lower temperature areaarea to a lower temperature area

Heat transferHeat transfer

BOILER TUBE

Transfer from Transfer from FURNACEFURNACE to to Boiler TubeBoiler Tube by by radiationradiation and and convectionconvection

Transfer Transfer through Boiler Tube wallthrough Boiler Tube wall by by conductionconduction Transfer to Transfer to Steam DrumSteam Drum via circulation of fluid via circulation of fluid

((convectionconvection))



TransferTransfer

2 Effects of heat 2 Effects of heat transfertransferWhen heat is transferred to/from a substance, When heat is transferred to/from a substance,

oneone of two effects may be realized of two effects may be realized

Temperature changeTemperature change–– a rise or fall a rise or fall in temperature is a in temperature is a sensible heatsensible heat effecteffect

Phase changePhase change– – (liquid-vapor, vapor-liquid, (liquid-vapor, vapor-liquid,

solid-liquid, liquid-solid)solid-liquid, liquid-solid) is a is a latent heatlatent heat effecteffect But not both simultaneouslyBut not both simultaneously

at least not in the same at least not in the same spacespace

LATENT heat

212o liquid

212o vapor

Saturation Conditions

300o steam

88o of SUPERHEAT

BOILER

SUPERHEATERSENSIBLE

heat

SENSIBLE heat

Transferring heat to 1 lb of Transferring heat to 1 lb of HH22OO

(at atmospheric pressure)(at atmospheric pressure) Temp (oF)

Heat (BTU)

SO

LID

SO

LID

-LIQ

UID

MIX

LIQ

UID

VA

PO

R

Sensible

Latent32

212LIQUID-VAPOR MIX

0

Transferring heat to 1 lb of Transferring heat to 1 lb of HH22OO

(at atmospheric pressure)(at atmospheric pressure)Temp (oF)

Heat (BTU)

Superheated VAPOR

212

LIQUID-VAPOR MIXSaturation Conditions: 0 psig; 212oF

0

Sub-cooled LIQUID

Sensible Heat 0.5 BTU/oF

0% “quality” (100% liquid)

BOILING

CONDENSINGLatent Heat *of vaporization) 970 BTU/lb

50% “quality” (50% liquid()

100% “quality” (0% liquid()

“wet” steam

Sensible Heat 1.0 BTU/oF

Boiling (saturation) Boiling (saturation) Temperature linked to Temperature linked to

pressurepressure

162o liquid

5 psig

1 Atm(14.7 psia)

0 psia

230o liquid

162o vapor

230o vapor

0 psia

1 Atm

10”Hg(bar)

20”Hg(VAC)

Saturation Temperatures & Saturation Temperatures & PressuresPressures

Temp (oF)

Heat (BTU)

212 1 Atm (14.7 psia, 0 psig)

0

92

490

570

600 psig

1200 psig

28.5 “Hg (VAC)

970 BTU/lb

1040 BTU/lb

728 BTU/lb

610 BTU/lb

STEAM DOMESTEAM DOME

Thermodynamic Thermodynamic CYCLESCYCLES

5 components:5 components:– Heat sourceHeat source– Heat sinkHeat sink– EngineEngine– PumpPump– Working FluidWorking Fluid

Closed Cycle:Closed Cycle: working fluid reused working fluid reused Open Cycle:Open Cycle: working fluid discarded working fluid discarded

Closed CycleClosed Cycle

ENGINE

HEAT SOURCE

HEAT SINK

PUMP

WORKING FLUID

W

HH

W

Open CycleOpen Cycle

ENGINEHEAT SOURCE

HEAT SINK

PUMP

WORKING FLUID

W

HH

W

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Thermodynamics