平均換熱系數(shù)公式及設(shè)置

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1、一）平均換熱系數(shù)公式平均換熱系數(shù)的計(jì)算公式為：，其中R為某一徑向坐標(biāo)，αR為該坐標(biāo)處的局部換熱系數(shù)。平均換熱系數(shù)局部換熱系數(shù)圖2.15下集管圓形射流壁面射流速度徑向變化曲線圖2.16下集管圓形射流換熱系數(shù)徑向分布曲線下集管圓形射流換熱特性的影響因素包括表面射流出口速度v0、射流的出口直徑D、射流出口距鋼板表面的距離H等。下集管射流的換熱系數(shù)隨射流出口距鋼板表面的距離H的增大而減小，其他因素對換熱特性的影響與上集管射流相同。下面還有設(shè)置平均平均換熱系數(shù)二）模型設(shè)置問題如圖WallFunc.HeatTran.Coef.定義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