chap1-introduction传热传质

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1、FundamentalsofHeatandMassTransferWhystudyheattransfer?HowtostudyChapter1IntroductionThermodynamics(热力学)dealswiththeendstatesoftheprocessduringwhichinteraction(workorheat)occursandprovidesnoinformationconcerningthenatureoftheinteractionorthetimerateatwhichitoccurs.Theobjectiveofthi

2、stext:toextendthermodynamicanalysisthroughstudyofthemodesofheattransferandthroughdevelopmentofrelationstocalculateheattransferrates.Chapter1IntroductionTheobjectivesofthischapter:(1)todevelopanappreciationforthefundamentalconceptsandprinciplesthatunderlieheattransferprocess;(2)toi

3、llustratethemannerinwhichaknowledgeofheattransfermaybeusedwiththefirstlawofthermodynamics(conservationofenergy)tosolveproblemsrelevanttotechnologyandsociety.1.1WhatandHow?Whatisheattransfer?(Definition):Heattransfer(orheat)isthermalenergyintransitduetoatemperaturedifference.Whenev

4、erthereexistsatemperaturedifferenceinamediumorbetweenmedia,heattransfermustoccur.Differencebetweenheattransferandthermodynamics:Thermodynamics:equilibrium,reversible,endstatesH.T:interaction,process,timerateHowisheattransferred?(H.T.Types,3modes)Werefertodifferenttypesofheattransf

5、erprocessesasmodes.Conduction(导热)Convection(对流)Radiation(热辐射)ConductionWhenatemperaturegradientexistsinastationarymedium,whichmaybeasolidorafluid,weusethetermconductiontorefertotheheattransferthatwilloccuracrossthemedium.ConvectionIncontrast,thetermconvectionreferstoheattransferth

6、atwilloccurbetweenasurfaceandamovingfluidwhentheyareatdifferenttemperatures.ThermalradiationAllsurfacesoffinitetemperatureemitenergyintheformofelectromagneticwaves.Hence,intheabsenceofaninterveningmedium,thereisnetheattransferbyradiationbetweentwosurfacesatdifferenttemperatures.1.

7、2PhysicalOriginsandRateEquations1.2.1Conduction:Atomic&molecularactivity(分子运动),EnergydiffusionConductionmaybeviewedasthetransferofenergyfromthemoreenergetictothelessenergeticparticlesofasubstanceduetointeractionsbetweenparticles.Gas:existstemperaturegradient,nobulkmotionHighertemp

8、eratureareassociatedwithhighermol