资源描述：
《传热专题小论文》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、WeaponstoFightAgainstColdWinterItbecomesmoreandmoreannoyingtogetthroughsuchcoldwinter.Girlsareborntobecrazyaboutbeauty,theycouldnotstandwearinglikeazongzi.Inanotherwords,westudentsdon’thaveanelectricstove,nottomentionanairconditioner,towarmourselves.Accordingtosuchcond
2、itions,somenewkindofheatingtoolsappear.Whenitcomestowarmingourselves,hot-waterbagscomefirst,nearly80%girlsaroundmeareusingthem,andevensomeboysarefansofthem.It’sconveniencemakethepopularity,asyoujustneedchargeitandafewminuteslater,youwillgetaheatedbag.Itisactuallyanener
3、gychangingprocessasitcovertselectricityintoheatbyboilingthewaterintheclosedbag.itappliesasimpleforcedcirculationsystemwithaseriespathjustasconvectionthroughtheliquidboundarylayerandintheformofboiling,conductionacrossthePVCcoverofthebag,conductionbetweenthebagandourhand
4、s.Firstlytheelectricitychangedintoheatviaanelectricresistance,thelargervaluetheresistanceis,themoreheatcanbeconverted.Andthentheheatfluxflowstothewaterbyconvectionthroughtheliquidboundarylayeradjacenttothemetalsurface.Itisfollowedthatthedensityofthoseheatedwaterdecreas
5、es,theyneedmoreroombutasvolumeislimitedtheywillmixwithothercoldwater,atlast,thewaterwouldbeboiledasaresultofthelocaltemperaturedifferenceandbubblesformedattheheattransfersurface.itisakindofphasechangeheatconvection.Afterthat,heatconductsfromtheinsidewalltotheoutsidewal
6、lofthebag.Moreoftenthannot,thebagismadeofPVCmaterialwithsomepropertiessuchasimpermeabilitytowaterandantioxidation.Takingconsumers’safetyintoconsideration,theconductivityofthePVCbagshouldbeneithertoogoodortoobad.Ifitconductsheatverywell,peoplemaybescaldoruncomfortable.C
7、onversely,badconductivitycouldnotmeetpeople’srequirement.What’smore,thewaterinthebagisnotthenormalwater,someionsareaddedtoimproveitsspecificheatcapacityandelectricalconductivity.Inaddition,heatpitch,inChinesewecalled“nuanbaobao”,isananotherkindofthelatestfashionablehea
8、ttool.Juststickitonourinnerclothesanditcangenerateheatover20hoursatmost.Manygirls,especiallythosewholikewearingskirts
