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1、传热学复习1（Reviewofheattransfer1）Intermediateheatingin2009--reviewofheattransferanditsanswersFirst,conceptualquestions1.Trytoanalyzetheheatdissipationprocessofindoorradiator.Whatheattransfermodesarethereineachlink?Takehotwaterinradiatortubeasanexample.Answer:thefollowingheatexcha
2、ngelinksandheattransfermode:(1)fromthehotwatertotheinnerwalloftheradiatorpipe,theheattransfermodeisforcedconvectionheattransfer;(2)fromtheinnerwalltotheouterwalloftheradiator,theheattransfermodeissolidheatconduction;(3)fromtheouterwalloftheradiatorpipetotheindoorair,thereisna
3、turalconvectionheattransferandradiationheattransferintheheattransfermode.2,trytoanalyzethewinterindoorairandoutdoorairthroughthewalloftheheattransferprocess,eachlinkwhatheattransfermode?Answer:thefollowingheatexchangelinksandheattransfermode:(1)indoorairtothewallofthewall,the
4、heattransfermodeisnaturalconvectionheattransferandradiationheattransfer;(2)theinnerwalltotheouterwallofthewall,theheattransfermodeissolidheatconduction;(3)theouterwallofthewalltotheoutdoorair,theheattransfermodehasconvectionheatexchangeandradiationheattransfer.3.Whatisthenorm
5、alstageofunsteadyheatconduction?Writeoutitsmainfeatures.Answer:theobjectintheheatingorcoolingprocess,thetemperaturearoundtheobjectswithinthetimerateofchangehascertainregularity,influenceofinitialtemperaturedistributiongraduallydisappear,thisstageiscalledanormalstageofunsteady
6、heatconduction.4.WriteouttheexpressionsofNu,Re,PrandBinumbers,andillustratetheirphysicalmeaning.Answer:(1)Nusel(Nusselt)number,whichrepresentsthesizeofthedimensionlesstemperaturegradientonthesurface.(2)Reynoldsnumber(Reynolds),whichrepresentstherelativesizeofinertiaforceandvi
7、scousforce.(3)Prandtlnumber,whichrepresentstherelativesizeofthemomentumdiffusionthicknessandtheenergydiffusionthickness.(4)Biotnumber,whichrepresentstherelativesizeofinternalthermalresistanceandexternalthermalresistanceofheatconductingbody.6,accordingtotheheatconductionmechan
8、ism,thethermalconductivityofthestateinthethreestatesofgas,liquidands
