第十章 对流换热

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1、第十章对流换热英文习题1.FindingconvectioncoefficientfromdragmeasurementA2m×3mflatplateissuspendedinaroom,andissubjectedtoairflowparalleltoitssurfacesalongits3-m-longside.Thefreestreamtemperatureandvelocityofairare20℃and7m/s.Thetotaldragforceactingontheplateismeasuredtobe0.86N.Determinetheav

2、erageconvectionheattransfercoefficientfortheplate(Fig.10-1).2.CoolingofahotblockbyforcedairathighelevationThelocalatmosphericpressureinDenver,Colorado(elevation1610m),is83.4kPa.Airatthispressureand20℃flowswithavelocityof8m/sovera1.5m×6mflatplatewhosetemperatureis140℃(Fig.10-2).De

3、terminetherateofheattransferfromtheplateiftheairflowsparalleltothe(a)6-m-longsideand(b)the1.5-mside.3.CoolingofasteelballbyforcedairA25-cm-diameterstainlesssteelball(ρ=8055kg/m3,andCp=480J/kg.℃)isremovedfromtheovenatauniformtemperatureof300℃.Theballisthensubjectedtotheflowofairat

4、1atmpressureand25℃withavelocityof3m/s.Thesurfacetemperatureoftheballeventuallydropsto200℃.Determinetheaverageconvectionheattransfercoefficientduringthiscoolingprocessandestimatehowlongtheprocesswilltake.4.FlowofoilinapipelinethroughtheicywatersofalakeConsidertheflowofoilat20℃ina3

5、0-cm-diameterpipelineatanaveragevelocityof2m/s(Fig.10-3).A200-m-longsectionofthepipelinepassesthroughicywatersofalakeat0℃.Measurementsindicatethatthesurfacetemperatureofthepipeisverynearly0℃.disregardingthermalresistanceofthepipematerial,determine(a)thetemperatureoftheoilwhenthep

6、ipeleavesthelake,(b)therateofheattransferfromtheoil.5.Heatlossthroughadouble-panewindowThevertical0.8-m-high,2-m-widedouble-panewindowshowninFig.10-3,consistsoftwosheetsofglassseparatedbya2-cmairgapatatmosphericpressure.Iftheglasssurfacetemperaturesacrosstheairgaparemeasuredtobe1

7、2℃and2℃,determinetherateofheattransferthroughthewindow.工程热力学与传热学第十章对流换热习题习题1.何谓表面传热系数？请写出其定义式并说明其物理意义。2.用实例简要说明对流换热的主要影响因素。3.对流换热微分方程组由几个方程组成，各自导出的理论依据是什么？4.何谓流动边界层和热边界层？他们的厚度是如何规定的？5.简述边界层理论的基本内容。6.边界层理论对求解对流换热问题有何意义？7.层流边界层和湍流边界层在传热机理上有何区别？8.何谓两个物理现象相似？9.简述相似理论的主要内容。10.如何判断两个现象

8、是否相似？11.相似理论对解决对流换热问题有何指导意义？12.分别写出努塞尔特数