一维稳态导热-传热学-课件-03.ppt

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1、Chapter3一维稳态导热One-dimensionalsteady-stateconduction一维稳态导热One-dimensionalsteady-stateconduction物体温度不随时间而变有内热源Withheatgeneration无内热源Withnoheatgeneration1通过平壁的导热Heatconductionthroughaplanewall1.1第一类边界条件Constantsurfacetemperature热导率为常数，=constant微分方程Heatequation边界条件Boundarycondition温度分布Th

2、etemperaturevarieslinearlywithx热流密度Heatflux热流量Heatrate材料热导率随温度而变=0(1+bt)微分方程Heatequation边界条件Boundarycondition温度分布Temperaturedistribution热流密度Heatflux多层平壁Compositewall热流密度Heatflux1.2第三类边界条件Convectionsurfacecondition微分方程Heatequation边界条件Boundarycondition多层平壁Compositewall多层复合平壁Series-par

3、allelcompositewallA1B1C1A2B2C2A3B3C3q热阻、热流量近似算法说明：材料导热系数相差较大时，应按二维和三维温度场计算。2通过圆筒壁的导热Heatconductionthroughacylindricalwall2.1第一类边界条件Constantsurfacetemperature热导率=C，圆筒内径r1，外径r2，长L微分方程Heatequation边界条件Boundarycondition温度分布Temperaturedistribution热流密度Heatflux热流量Heatrate多层圆筒壁Compositecylin

4、dricalwall热流量Heatrate2.2第三类边界条件Convectionsurfacecondition已知：r=r1侧流体温度tf1，换热系数h1r=r2侧流体温度tf2，换热系数h2边界条件多层圆筒壁Compositecylindricalwall3通过空心球壁的导热Heatconductionthroughasphericalshell第一类边界条件Constantsurfacetemperature热导率=C,圆筒内径r1,外径r2,无内热源微分方程Heatequation边界条件Boundarycondition温度分布Temperature

5、distribution热流密度Heatflux热流量Heatrate4导热形状因子ConductionshapefactorWhereSistheconductionshapefactor.ConductionshapefactorOne-dimensionalconductioninaplanewallOne-dimensionalconductioninacylindricalwallOne-dimensionalconductioninasphericalwall5临界热绝缘直径(或半径)Criticalinsulationdiameter(orradiu

6、s)设管长L=1因此，Rtot存在极小值，即此时热损失最大。临界热绝缘直径(或半径)6接触热阻Thermalcontactresistance定义：当导热过程在两个直接接触的固体间进行时，由于表面不是理想的平整，所以界面容易出现点接触，给导热过程带来额外的热阻，称为接触热阻。符号：Rc单位：m2·K/W7延伸体的导热HeatconductionfromextendedsurfacesFinconfigurations延伸体的种类StraightFinsofuniformcrosssection7.1等截面直肋假设(Assumptions)One-dimension

7、alsteady-stateconductioninthexdirectionThermalconductivityisconstantRadiationfromthesurfaceisnegligibleConvectionheattransfercoefficienthisuniformoverthesurfaceBi=hlc/s<0.1where,BiisBiotnumber,adimensionalparameterlcischaracteristiclength(特征尺寸)lc=Cross-sectionalArea(截面积)/Perimeter(周长

8、)Rect