Chapter3TheFirstLawof

Thermodynamics:

ClosedSystem

3-1-1ConservationofenergyprincipleEnergycanbeneithercreatednordestroyed;itcanonlychangeforms3-1IntroductionToTheFirst

LawofThermodynamics3-1-2TheFirstLawofThermodynamicsNeitherheatnorworkcanbedestroyed;theycanonlychangefromonetoanother,thatis:

3-1-2TheshortcomingsofQ=WCan’tbeemployedinengineeringcalculationCan’tshowthequalitydifferencebetweenheatandworkInengineeringareawewouldratheruseaformulalikethis:ThenetchangeinthetotalenergyofthesystemThenetenergytransferredtothesystem-Thenetenergytransferredfromthesystem=

3-2Work3-2-1Definition:workistheenergytransferassociatedwithaforceactingthroughadistanceWorkisenergyintransitionDenotedbyW----------kJworkonaunit-massbasisisdenotedbyww----------kJ/kgworkdoneperunittimeiscalledpowerpowerisdenotedas

3-2-2PositiveandnegativeSinceworkistheenergytransferredbetweensystemanditsboundary,thenwedefinethat:workdonebyasystemispositive;andworkdoneonasystemisnegative

3-3-1Movingboundarywork3-3MechanicalformsofWork

workdoneperunit:P-vChart

ReversibleProcessAprocessthatnotonlysystemitselfbutalsosystemandsurroundingkeepsequilibriumTheconditionoftheformulaIsthat:Systemundergoesareversibleprocess

3-3-2Gravitationalwork

3-3-3Accelerationalwork

3-3HeatTransfer3-3-1Definition:Heatisdefinedastheformofenergythatistransferredbetweentwosystemsduetotemperaturedifference.HeatisenergyintransitiondenoteasQ----------kJheattransferredperunitmassofasystemisdenotedasq----------kJ/kgWedefineheatabsorbedbyasystemispositive

3-3-3ModesofHeatTransfer:Conduction:3-3-2HistoricalBackground