平均换热系数公式及设置

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1、一）平均换热系数公式平均换热系数的计算公式为：，其中R为某一径向坐标，αR为该坐标处的局部换热系数。平均换热系数局部换热系数图2.15下集管圆形射流壁面射流速度径向变化曲线图2.16下集管圆形射流换热系数径向分布曲线下集管圆形射流换热特性的影响因素包括表面射流出口速度v0、射流的出口直径D、射流出口距钢板表面的距离H等。下集管射流的换热系数随射流出口距钢板表面的距离H的增大而减小，其他因素对换热特性的影响与上集管射流相同。下面还有设置平均平均换热系数二）模型设置问题如图WallFunc.HeatTran.Coef.定义WallFunc.HeatTran.Coef.isdefine

2、dbytheequation(30.4-44)whereisthespecificheat,istheturbulencekineticenergyatpoint,andisdefinedinEquation12.10-5.Thelaw-of-the-wallimplementedinFLUENThasthefollowingcompositeform:(12.10-5)whereiscomputedbyusingtheformulagivenbyJayatilleke[165]:(12.10-6)and=turbulentkineticenergyatpointP=densit

3、yoffluid=specificheatoffluid=wallheatflux=temperatureatthecelladjacenttowall=temperatureatthewall=molecularPrandtlnumber()=turbulentPrandtlnumber(0.85atthewall)=VanDriestconstant(=26)=meanvelocitymagnitudeatNotethat,forthepressure-basedsolver,thetermsandwillbeincludedinEquation12.10-5onlyforc

4、ompressibleflowcalculations.Thenon-dimensionalthermalsublayerthickness,,inEquation12.10-5iscomputedasthevalueatwhichthelinearlawandthelogarithmiclawintersect,giventhemolecularPrandtlnumberofthefluidbeingmodeled.Theprocedureofapplyingthelaw-of-the-wallfortemperatureisasfollows.Oncethephysicalp

5、ropertiesofthefluidbeingmodeledarespecified,itsmolecularPrandtlnumberiscomputed.Then,giventhemolecularPrandtlnumber,thethermalsublayerthickness,,iscomputedfromtheintersectionofthelinearandlogarithmicprofiles,andstored.Duringtheiteration,dependingonthevalueatthenear-wallcell,eitherthelinearort

6、helogarithmicprofileinEquation12.10-5isappliedtocomputethewalltemperatureorheatflux(dependingonthetypeofthethermalboundaryconditions).ThefunctionforgivenbyequationEquation12.10-6isrelevantforthesmoothwalls.Fortheroughwalls,however,thisfunctionismodifiedasfollows:(12.10-7)whereisthewallfunctio

7、nconstantmodifiedfortheroughwalls,definedby.Tofindadescriptionoftheroughnessfunction,youmayrefertoEquation7.13-3inSection7.13.1.SurfaceHeatTransferCoef.(intheWallFluxes...category),asdefinedinFLUENT,isgivenbytheequation(30.4-33)whereisthecomb