建筑环境与能源应用工程专业英语.ppt

,LessonFiveHeatTransfer,Topics,Wordslearning,Introducitonofheattransfer,Workingsitepictures,Textlerning,heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热(速)率temperaturedifference温差factorofsafety安全系数experimentalerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:conduction传导convection对流radiation辐射,heattransferequipment传热设备heatexchanger热交换器boiler锅炉condenser冷凝器radiator散热器refrigerator冰箱solarcollector太阳能集热器heattransferrate传热(速)率temperaturedifference温差factorofsafety安全系数experimentalerror实验误差operatingcondition运行条件heattransfercoefficient传热系数undertheseadverseconditions在最不利工况下threeformsofheattransfer:conduction传导convection对流radiation辐射,Topicone:Frequentlyusedwordsandphrases,HeatSensibleHeatLatentHeat,duetomolecularthermalmotion,Solidificationfusion,Liquefactionevaporation,Topictwo:Introducitonofheattransfer,Conduction,Convection,Radiation,Threeformsofheattransfer,Forsteady-stateheatconductioninonedimension,theFourierlawis,temperaturegradient,cross-sectionalareanormaltoflow,thermalconductivity,heatflowrate,Equation(1)statesthattheheatflowrateqinthexdirectionisdirectlyproportionaltothetemperaturegradientdt/dxandthecross-sectionalareaAnormaltotheheatflow.Theproportionalityfactoristhethermalconductivity.Theminussignindicatesthattheheatflowispositiveinthedirectionofdecreasingtemperature.Conductivityvaluesaresometimesgiveninotherunits,butconsistentunitsmustbeusedinEquation(1).,(1),Thefundamentalequationforunsteady-stateconductioninsolidsorfluidsinwhichthereisnosubstantialmotionis,wherethermaldiffusivityistheratio/cp;isthermalconductivity;,density;andcp,specificheat.Ifislarge(highconductivity,lowdensityandspecificheat,orboth),heatwilldiffusefaster.,Isthereanymistakes?,Heattransferinvolvingmotioninafluidduetothedifferenceindensityandtheactionofgravityiscallednaturalconvectionorfreeconvection.Heattransfercoefficientsassociatedwithgasesfornaturalconvectionaregenerallymuchlowerthanthoseforforcedconvection.Forcedaircoolersandheaters,forcedair-orwater-cooledcondensersandevaporators,areexamplesofequipmentthattransferheatprimarilybyforcedconvection.Whenfluidflowsoveraflatplate,aboundarylayerformsadjacenttotheplate.Thevelocityofthefluidattheplatesurfaceiszeroandincreasestoitsmaximumfreestreamvaluejustpasttheedgeoftheboundarylayer.,Radiation,oneofthebasicmechanismsforenergytransferbetweendifferenttemperatureregions,isdistinguishedfromconductionandconvectioninthatitdoesnotdependonanintermediatematerialasacarrierofenergybutratherisimpededbythepresenceofmaterialbetweentheregions.Therateofthermalradiantenergyemittedbyasurfacedependsonitsabsolutetemperature.Asurfaceiscalledblackifitcanabsorballincidentradiation.ThetotalenergyemittedperunittimeperunitareaofblacksurfaceWbtothehemisphericalregionaboveitisgivenbytheStefan-Boltzmannlaw.,whereWbisthetotalrateofenergyemissionperunitarea,andistheStefan-Boltzmannconstant5.670108W/(m2K4).,Infiltration,zeroenergybuildinglowenergybuilding,TypicalFeaturesIncreasedceilingandwallinsulationRadiantbarrierLowairinfiltrationrateHigh-performancewindowsEngineeredHVACTightductinstallationAll-fluorescentlightingPhotovoltaic(PV)solar-electricsystem,1.Introductionheattransferproblemsencounteredinpractice(1)rating(2)sizingtwokindsofapproachforthestudyofheattransfer(1)experimentally(2)analytically2.ModelinginHeatTransfermodelinginheattransferandtheproblemsencounteredaveryaccuratebutcomplexmodelasimplebutnot-so-accuratemodel3.EngineeringSoftwarePackagesNeitherwillengineeringsoftwarepackagesreplacethetraditionalengineeringcourses.Andwhy?,TopicFour:Textlearning,Theheattransferproblemsencounteredinpracticecanbeconsideredintwogroups:(1)ratingand(2)sizingproblems.2.However,thisapproachisexpensive,time-consuming,andoftenimpractical.3.thesizeofaheatingsystemofabuildingmustusuallybedeterminedbeforethebuildingisactuallybuiltonthebasisofthedimensionsandspecificationsgiven.,encounteredinpractice:现实中遇到的ratingproblem:速率问题sizingproblem:容量选择的问题,time-consuming:耗时的,dimension:规模尺寸、维3-D：？specification:（工程）说明书,4.theresultsobtainedaresubjecttotheaccuracyoftheassumptionsandidealizationsmadeintheanalysis.5.Inheattransferstudies,oftenagoodcompromiseisreachedbyreducingthechoicestojustafewbyanalysis,andthenverifyingthefindingsexperimentallyanddoingsomefine-tuning.,subjectto:受支配，取决于makeaassumption(idealization)in:在中作了假设（理想化）,reachacompromise:达到一种折衷或平衡fine:细微地,精巧地tune:调整fine-tuning：？,6.Inthelimitingcaseofinfinitesimalordifferentialchangesinvariables,weobtaindifferentialequationsthatprovideprecisemathematicalformulationsforthephysicalprinciplesandlawsbyrepresentingtheratesofchangesasderivatives.7.Theequationitselfisveryinstructiveasitshowsthedegreeofdependenceofsomevariablesonothers,andtherelativeimportanceofvariousterms.,infinitesimal:无穷小、无穷小的infinite:无穷大、无穷大的variable:变量constant:？differentialequation:微分方程integral：积分、积分的calculus:微积分derivative:派生的事物，导数,instructive:指导性的variousterms:不同变量,8.Manyprocessesthatseemtooccurinnaturerandomlyandwithoutanyorderare,infact,beinggovernedbysomevisibleornot-so-visiblephysicallaws.9.Thisiswherethepowerofanalysislies.10.Ananalystworkingonanengineeringproblemoftenfindshimselforherselfinapositiontomakeachoicebetweenaveryaccuratebutcomplexmodel,andasimplebutnot-so-accuratemodel.,occurrandomly:随机发生withoutanyorder:无序not-so-visible:不（那么）可见的not-so-+adj,lie:存在Thesolutionliesinresearch.?,makeachoicebetween:在之间作出选择（抉择）,11.Forexample,theprocessofbakingpotatoesorroastingaroundchunkofbeefinanovencanbestudiedanalyticallyinasimplewaybymodelingthepotatoortheroastasasphericalsolidballthathasthepropertiesofwater.12.Forexample,whenpurchasingaheatexchangerthatwillhandlehardwater,wemustconsiderthatsomecalciumdepositswillformontheheattransfersurfacesovertime,causingfoulingandthusagradualdeclineinperformance.,modelas:将模型化为，将视为spherical:球形的hemi-:“半”hemispherical:?hemisphere:?,calciumdeposits:钙的沉积物calciumcarbonate:碳酸钙fouling:结垢declineinperformance:性能的降低,13.Attheminimum,themodelshouldreflecttheessentialfeaturesofthephysicalproblemitrepresents.,Attheminimum:至少essentialfeatures:基本特征,14.Therearemanysignificantreal-worldproblemsthatcanbeanalyzedwithasimplemodel.,real-worldproblem:实际问题,15.Butitshouldalwaysbekeptinmindthattheresultsobtainedfromananalysisareasaccurateastheassumptionsmadeinsimplifyingtheproblem.16.Therefore,thesolutionobtainedshouldnotbeappliedtosituationsforwhichtheoriginalassumptionsdonothold.,hold:使有效、可行或真实Thetheoryholds.Thisisanobservationthatstillholdstrue.,bekeptinmind:牢记,17.Asolutionthatisnotquiteconsistentwiththeobservednatureoftheproblemindicatesthatthemathematicalmodelusedistoocrude.18.Thusanysolutiontoaproblemshouldbeinterpretedwithinthecontextofhowthatproblemisformulated.19.Afterall,almostalltheheattransferproblemswearelikelytoencounterinpracticecanbesolvedusingoneofseveralsophisticatedsoftwarepackagesreadilyavailableinthemarkettoday.,beconsistentwith:与一致crude:粗略的，天然的、未加工的crudeoil:?crudesalt:?,softwarepackage:软件包readily:容易地,interpret:解释、说明context:上下文、背景formulate:用公式表示,Thesesoftwarepackagesnotonlygivethedesirednumericalresults,butalsosupplytheoutputsincolorfulgraphicalformforimpressivepresentations.Itisunthinkabletopracticeengineeringtodaywithoutusingsomeofthesepackages.,impressive:给人印象深刻的presentation:表达、表现,practice:从事engineering:工程（学）theCollegeofCivilEngineering:?BuiltEnvironmentandServiceEngineering:?theChineseAcademyofengineering:?theChineseAcademyofSciences:?theChineseAcademyofSocialSciences:?,22.Thistremendouscomputingpoweravailabletousatthetouchofabuttonisbothablessingandacurse.,atthetouchofabutton:按一下按键,23.Inthehandsofpoorlyeducatedpeople,thesesoftwarepackagesareasdangerousassophisticatedpowerfulweaponsinthehandsofpoorlytrainedsoldiers.,poorlyeducated：未受过良好教育的highlyeducated:受过良好教育的sophisticated:尖端的、先进的poorlytrained:未受过良好培训的,24.Ifitweretruethattheengineeringstudentsdonotneedallthesefundamentalcoursestheyaretakingbecausepracticallyeverythingcanbedonebycomputersquicklyandeasily,thenitwouldalsobetruethattheemployerswouldnolongerneedhigh-salariedengineerssinceanypersonwhoknowshowtouseaword-processingprogramcanalsolearnhowtousethosesoftwarepackages.,engineeringstudents:工科学生sciencestudents:理科学生artsstudents:文科学生high-salaried:高薪的word-processingprogram:文字处理程序,25.Butthestatisticsshowthattheneedforengineersisontherise,notonthedecline,despitetheavailabilityofthesepowerfulpackages.26.Weshouldalwaysrememberthatallthecomputingpowerandtheengineeringsoftwarepackagesavailabletodayarejusttools,andtoolshavemeaningonlyinthehandsofmasters.,statistics:统计数字统计学mathematicalstatistics:?theoryofprobability:?show:显示、表明resultsshowthat:结果表明,howtotranslate?,27.Havingthebestword-processingprogramdoesnomakeapersonagoodwriter,butitcertainlymakesthejobofagoodwritermucheasierandmakesthewritermoreproductive.,make注意用法howtotranslate?,28.Thatis,moretimewillbespentintheclassroomsdiscussingthephysicalaspectsoftheproblemsingreaterdetail,andlesstimeonthemechanicsofsolutionprocedures.,mechanics:技巧，机械学、力学,29.Neitherwillengineeringsoftwarepackagesreplacethetraditionalengineeringcourses.30.Theywillsimplycauseashiftinemphasisinthecoursesfrommathematicstophysics.,traditional:传统的conventional:?traditionalmethodtraditionalmodeltraditionalapproach,shift:转变、轮（换）班,轮班职工;轮班工作时间aneight-hourshift:八