外文翻译-温差发电技术的研究进展及现状

Thermoelectricpowergeneration,alsocalledthermoelectricpowergeneration,isakindofgreenenvironmentalprotection.Thethermoelectricpowergenerationtechnologyhastheadvantagesofsimplestructure,stronganddurable,nomovingparts,nonoise,longservicelife,etc..Canmakereasonableuseofsolarenergy,geothermalenergy,industrialwasteheatandlowgradeenergyintoelectricity.Theresearchofthermoelectricpowergenerationtechnologybeganin1940s.Becauseofitssignificantadvantages,thermoelectricpowergenerationinaviation,militaryandotherfieldshasbeenwidelyused,theUnitedStates,formerSovietUnionhasdevelopedathousandsofradioisotopeornuclearreactortemperaturedifferencegeneratorusedasemptyasked,marineequipmentofpowersupply.Withtheincreasingdepletionoffossilenergy,theUnitedStates,Japan,theEuropeanUnionandotherdevelopedcountriespaymoreattentiontotheresearchofthermoelectricpowergenerationtechnologyinthecivilfield,andhasmadeconsiderableprogress.Researchindomesticthermalpowergeneration,mainlyinelectricaltheoryandthermoelectricmaterialsbyresearch,aimedattemperaturehairappliancesoptimizationandprovidetheoreticalguidanceforthepreparationofthermoelectricmaterialswithexcellentproperties,althoughChinaistheworldlargestsemiconductorthermoelectricdeviceoutputcountry,butinthetemperaturedifferencehairappliancesintegrateddesignandapplicationresearchisstillverylack.Therefore,thestudyofthermoelectricpowergenerationhasaveryrealisticsignificance.Isintroducedinthispaperprincipleofthermoelectrictechnology,reviewstheresearchprogressandstatusquoofdomesticandforeign,tocommoncommercialthermoelectricmoduleasanexample,thepowergenerationefficiencyofthermoelectricpowergenerationinthepresenceoflow,thermoelectricitycomponentandshortservicelife,reliabilityareanalyzed,andcountermeasuresareputforward.Withtheimprovementoftheperformanceofthermoelectricmaterialsandtheincreaseofthereliabilityofthermoelectriccomponents,theapplicationofthermoelectricpowergenerationhasabroadprospect.1workingprincipleCompletethetemperaturedifference,sothathightemperaturethermoelectricpowerisbasedonthermoelectricmaterialSeebeckeffectdevelopedapowergenerationtechnology,thePtypeandNtypetwokindofdifferenttypesofthermoelectricmaterials(Ptypeholerichmaterials,Ntypeiselectronrichmaterial)isconnectedtotheformationofaPNjunction,isplacedinahightemperaturestate,andtheotherendisformedatlowtemperature,duetothethermalexcitation,pifthereexistsalocallyconnected)typematerialendhole(electron)concentrationishigherthanthatofthelowtemperatureend,sointhisconcentrationgradientdrivenBu,holesandelectronstothelowtemperaturesidediffusion,resultingintheformationofelectricpotentialthermoelectricmaterialsthroughthelowtemperatureendofthehightemperatureendoftheinputofheatenergydirectlyintoelectricalenergy.APNjunctionalone,electromotiveforcecanbeformedisverysmall,andifsomanyseriesofPNjunctionCome,cangetenoughhighvoltage,becomeathermoelectricpowerplant2domesticandinternationalthermoelectricpowergenerationtechnologyresearchprogress2.1researchprogressinforeigncountriesSincethediscoveryoftheSeebeckeffectsince1821Seebeck,foreignthethermoelectricgenerationofalargenumberofstudies,in1947,firstthethermoelectricgeneratoravailable,efficiencyisonly1.5%.In1953,Loffeacademicianresearchteamsuccessfullydevelopedtheuseofcoaloillamps,tractorheatasaheatsourceofthermoelectricpowerplant,intheuseofelectricitydifficultareasforsmallpowersupply.Inthesixtiesofthe20thcentury,somematerialswithgoodthermoelectricproperties,theresearchupsurgeofthermoelectricpowergenerationreachedapeak,especiallytheformerSovietUnionandtheUnitedStates,duetothepromotionofnationaldefense,militaryandotherspecialindustry,applicationanddevelopmentofthermoelectricgenerationtechnologyrapidly.Bytheendof1960s,theformerSovietUnionhasmademorethan1000radioactiveisotopethermoelectricgenerator(RTG),whichiswidelyusedinsatellitepowersupply,beaconandnavigationmark,anditsaverageservicelifeismorethan10years.TheUnitedStatesisalsounwillingtolagbehind,anditsdevelopmentofthelongestRTGworkQuestionhasbeenover30years.June1961U.S.SNAP-3Aenergysystemsputintouse,theoutputpowerof2.7W,powergenerationefficiencyof5.1%.TheRTG}outputpower,whichwasusedonthelaunchofJupiterandSaturnin1977,hasreached155W.Inearly1980s,theUnitedStatescompletedthedevelopmentofthe500-1000Wmilitarythermoelectricgenerator,andinthelate80'stoenterthearmyequipment.Withtheenergycrisisandenvironmentalpollution,peoplebegantopayattentiontothevalueofthermoelectricpowergenerationinwasteheatutilization,manycountrieshavedevelopedthermoelectrictechnologyasamediumandlong-termenergydevelopmentplan.Japanlaunchedaseriesofto"solidwastecombustionenergyrecoveryresearchprogram"inthetitleofthegovernmentplanisstudiedforthesolidwasteincinerationfurnacewasteheatpowergenerationtechnology,combiningtheturbinesandthermoelectricgenerator,toachievemaximumutilizationoftheheatofthedifferentscalegarbageincineration.2003NovemberU.S.DepartmentofEnergyannouncedfundedPacificNorthwestNationalLaboratory,MichiganTechnologyUniversityandotherunits,focusingontheirresearchinhighperformancethermoelectricmaterialsandapplicationtechnology,especiallytheuseofindustrialwasteheat.Inrecentyears,theutilizationofthelowgradeheatsourcehasbecomethemaindirectionoftheresearchonthetechnologyofthermalpowergeneration.Maneewan,suchastheuseofsteelplateplacedontheroofofthesolarcollectortoabsorbtheheatandtheenvironmentofthetemperaturedifferencebetweenpowergeneration,todrivetheaxialflowwind})Ltoguidethenaturalconvectionoftheroofair,soastocooltheroof.Ridaandsoon,thethermalsideofthethermoelectricgeneratorisconnectedwiththeouterwallofthecookingstoveinthecountry,andthecoldendisarrangedintheair,andthetemperatureofthefurnacewallandtheenvironmentareusedtogenerateelectricity,andtheoutputpoweris4.2W.HASEBEetal.Thesummerhightemperaturesurfaceastheheatsource,heatexchangetubeforthecollector.By19groupsofthermoelectriccomponents.Intheheatpipeliquidflowrateis0.7L/min,outputpowerof3.6wthacher,fundedbytheU.S.DepartmentofenergyandNewYorkStateEnergyResearchanddevelopmentauthorityinthedevelopmentofvehicleexhaustwasteheatpowergenerationsystem,theuseofthegroupof20hz-20thermoelectricmodule,thermoelectricmaterialsforBitebasedmaterials,vehiclespeedof112km/h,maximumtemperaturedifference174DEGC,maximumoutputpowerof255W,2006,bsstscientistsandBMWjointlyannounced,commercialvehicletemperaturedifferencegeneratorwillbeputintooperationin2013.Douglasandsoonthedynamicchangeoftheheatsource,thedesignofmultimoduleInteractionLoopthermoelectricgenerator,underthesameheatsource,themaximumoutputpowerincreasedby25%.2.2domesticresearchprogressDomesticresearchonthermoelectricpowergenerationisrelativelylate,anditismainlyfocusedontheresearchofthetheoryandthepreparationofthermoelectricmaterials.ChenJincanresearchgroupfrom1980sbegantostudythebasictheoryofthermoelectricgenerator,thethermoelectricpropertiesoftheoptimizationandanalysis,getalotofmeaningfulresults[no.QuJianetal.LiYudongetal.Analysisoftheperformanceofthelowtemperaturedifferencegeneratorfromthepointofviewofexergy.JiaLeietal.TheinfluenceofThompsonGeontheoutputpowerofthelowtemperatureandlargetemperaturedifferenceconditionscannotbeignored.JiaYangEtc.atemperaturethermoelectriccouplinganalysismodel,tothenumericalcalculationmethodanalysisthethermoelectricmaterialparametersandtheirvariationonelectricalcharacteristicsof,drawtheconclusion,materialthermalconductivity,electricalresistivityandSeebeckcoefficientonthegeneratorefficiencyofconversionarenonlinear,whichinfluencecoefficientofthermalconductivityofthemostobvious.DePeng,andanalysisthethermoelectricthermalenvironment,looploadresistanceparametersandthermoelectricmonomersofconnectionwaysofoperatingperformanceoftheelectricappliance,itisconcludedthattoimprovethermoelectricgeneratoratthehotendheatfluxorincreasedcoldendoftheheattransfercoefficientcanincreasetheelectricaloutputpowerandtheefficiencyofthermoelectricconversionofconclusion.SuJingfangstudiedthesystem.Andtheenvironment,systemandsystemoffluxrelation,propertiesofthesystemtomakeoptimizationbasedthermoelectricgeneratoroptimizationdesignmodel,andusingVB6.0(MicrosoftVisualBasic6.0)languageasadevelopmenttool,ActiveXDataObjectAccessdatabase,thepreparationofthethermoelectricgeneratordesignsoftware.QianWeiqiangthroughstudyontheelectricalpropertiesoflowgradeheatsourceofsmallsemiconductortemperaturedifference,summarizestheelectromotiveforceandinternalresistanceandtransmissionpowerparameterchangeswiththeexternalcircuit,temperature,generatingmodulegeometryfactors.Wealsostudytheseriesandparallelconnectionthermoelectricmoduleperformance.Fromthepointofviewofnon-equilibriumthermodynamics,themodelofthelowtemperaturedifferenceofthesinglelayerandmultipleelectricappliancesinthelowtemperatureandlowtemperaturestabilitywasestablished.StudyonthermoelectricgeneratorintheinternalstructureandexternalforthemovementofthethermalconditionsBu,combinedwithexperiment,itisconcludedthatthebestmatchingcoefficients,poweroutputandefficiencyarewiththemaximumtemperaturedifferenceapproximatelinearly,andpointsoutthepowergenerationefficiencyislowintheroottherelyontheimprovementofthematerialproperties.Justeastoftheoreticalanalysisandexperimentalstudycombinedbysimulatingthetankventtubeneartheareaofrefrigeratingcondition,bycoolingconditionevaluationofinfraredstealtheffect,itisconcludedthattotankexhaustwasteheatastheheatsourcewillbetheapplicationofthermoelectrictechnologytothetanks,infraredstealthfeasibleconclusion.3.1generationefficiencyAtpresent,theefficiencyofthermoelectricpowergenerationisgenerally5%-7%,farlessthan40%ofthermalpowergeneration.Themainreasonisthattheperformanceofthermoelectricmaterialsisnotgood,ontheotherhandisthematchingofelectricalappliancesfactory.3.1.1thermoelectricmaterialsThermoelectricmaterials,asthecorepartofthermoelectricdevices,directlydeterminetheperformanceofthedevice.TheoptimalvalueofZTisthemostimportantparametertomeasuretheperformanceofthermoelectricmaterials.ThehighertheZTvalue,thebetterthethermoelectricpropertiesofthematerials,thehighertheenergyconversionefficiency.Bi2T3;roomtemperatureZTvalueofabout1,isthemostwidelyusedthermoelectricmaterials.ButthethermoelectricpowergenerationefficiencyofBi2T3materialsisstilllessthan10%.IftheZTvalueofthematerialcanbeincreasedtoabout3,thedifferenceintemperaturewillbecomparabletothatoftheconventionalpowergeneration.Therefore,peopleareactivelylookingforanddevelopmentofhighmeritofnewthermoelectricmaterials,thepresentresearchhotspots:cobaltbasedoxidethermoelectricmaterials,quasicrystalmaterials,superlatticethermoelectricmaterials,nanothermoelectricmaterials.TerasakidiscoveredforthefirsttimeNaCo2O4singlecrystalatroomtemperatureBuhasahigherSeebeckcoefficient,lowresistivityandlowthermalconductivity,thiscausedpeople'sattention,butNaCo2O4inairdeliquescentandmorethan1073Kvolatile,sopeoplelooktoanotherdrillbasedoxidesofCa-Co-Osystem.TheFunahashistudypredicts:Ca2Co2O5inT=873K,ZT=1.22.7.Quasicrystallinethermoelectricmaterialsin1984byShechtmanandotherfirstfoundthatinrecentyearscausedconcern.Thiskindofmaterialhasgoodthermodynamicstability,highresistivity,andhasanegativecoefficientofthermalconductivity,sotheconductiveperformanceisgood,andthethermalconductivityislow.AquasicrystallinethermoelectricmaterialwithZT=1.6atroomtemperaturewaspredicted.Thesuperlatticeisamultilayerheterogeneousstructureformedbytheperiodicalternatinggrowthoftwokindsofsemiconductorsinglecrystalfilms,andeachlayercontainsseveralorevenseverallayers.Duetothespecialstructureandsemiconductorsuperlatticeelectrons(orholes)energywillappearnewquantization,resultingintheincreaseofthedensityofStatesandthereforesuperlatticematerialwithmanynewfeatures.VenkatasubramanianandothermetalorganiccompoundsGasphasedeposition(MOCVE)methodtoprepareBi-Tebasedalloyfilm,ZTvaluereached2.4300K.DresselhausofBinanowiresandquantumwellsystemafteralargenumberofstudiespredictedthatthequantumconfinementeffectcanbeobtainedbysuperlatticeZTvalueofmorethan3ofthematerial.Nanothermoelectricmaterialsisanotherhotresearchtopicinthefieldofthermoelectricmaterials,andtheachievementsareoutstandinginthefieldofZhejiangUniversity.ZhaoXinbingandotherresearchfoundthatthetraditionalBi-Tebasedthermoelectricmaterialstoadd15%containingBi2T3;nanotubepowder,canmakethethermoelectricpropertiesofmaterialsincreasedbyabout20%.Cao,ZT=1.28(Bi,Sb)2Te3wereobtainedbyhydrothermalsynthesis.ZHAOandsoonthroughthenanometerpowderdoping,theZTvalueispreparedtoexceed1.5oftheBi2Te3-Sb2Te3andGeTe-AgSbTe2nanostructurematerials.3.1.2matchingproblemOutputpowerandpowergenerationefficiencyofthermoelectricgeneratorandhightemperatureendtemperature(Th).Lowtemperature(Tc),thermoelectricpowergenerationcircuitcurrent(I),loadresistance(R),electricalresistance(R)andotherfactorsarecloselyrelated.Underdifferentconditions,thedifferenceoftheperformanceofthethermoelectricgeneratorisgreat.QuJianandotherapplicationsoffinitetimethermodynamictheorytoanalyzetheworkingperformanceofthermoelectricgenerator,andgettheconclusionthatthereisthebestparameterworkingarea.PanYuZhuo,suchastheuseofnonequilibriumthermodynamicsoptimizationcontroltheoryanalysisofthermoelectricmodel,numericalsimulationresultsshowthatthematchingundertheconditionoftheworkingparametersofoutputpowerandgeneratingefficiencycanbewereincreasedby39%and20%electricalthermaldesignisalsoaffectingpowergenerationefficiencyareimportantfactors.Inordertomaintainahightemperature,oftenincreasetheheatdissipationdevicegeneratorinlowtemperatureside,sothattheheatdissipationinatimelymanner.Cheinstudynotedthatwhenthedevicethermalresistanceisgreaterthanthemaximumresistanceoftheradiator,theradiatorwillsmallcandispersewalkingdevicegeneratesheat,andthereforethermoelectricgeneratormatchingthecoldendheatdissipationwayalsoaffecttheelectricalperformanceoftheimportantfactors.Atpresentthemainheatdissipationmethod:airandliquidcoolingandheattransformation.Aircoolingisdividedintonaturalandforcedaircooling.Naturalair-cooledheatexchangerisacertainshapeoffinradiator.Theheatresistanceisdirectlyrelatedtothefindensityandtheareaoftheradiator.Thethermoelectricarewidelyappliedintheelectricapplianceisforcedaircooling,radiator(heatsink)combinedwiththefan,coldendheatconductiontothelargerareaoffinwithforcedcoolingheatdissipationintotheair.Thethermalresistancedependsonthewindspeed,thegreaterthewindspeed,thesmallerthethermalresistance.Forcedaircoolingcaneffectivelyimprovetheheattransfercoefficientoftheheatsink,reducetheheatdissipationarea,andthestructureissimple,easytoimplement,soitiswidelyused.Duetoaunitofliquidheatcapacitywassignificantlylargerthanthatofthegas,andliquidcoolingthanair-cooledhasbettercoolingeffect.Studieshaveshownthatliquidcoolingforheattransfercoefficientthanthenaturalaircoolingof100to1000times,sizeonthermalresistancemainlyandliquidflowvelocity,flowislarge,thermalresistanceislow.Atpresent,theliquidcoolingmethodsmainlyincludeliquidjetcooling,microchannelliquidcoolingandmacrowatercooling.Phasechangeheatdissipationistousephasechangematerialphasechangetoabsorbheattoheat.Theheatdissipationmethodissuitablefortheapplicationoftheintermittentworkingsituation,andthemostresearchistheheatdissipationwithphasechangeheatsiphontube.TheresultsofEsartetshowthatthephasetransitionheatsiphoncanobviouslyimprovetheuniformityofheatfluxontheheattransfersurface,reducethethermalresistanceandheatdissipation.3.2reliabilityissuesTheexistenceof3.2.1andmechanicalstressTocommonsandwichtypethermoelectricmodule,forexample,toachievehighpowergenerationefficiency,usuallyrequirepowercomponentsinhotandcoldendformingalargertemperaturedifference,whichwillcausecoldendisconnectedattheendoftheshrinkageorthermalconnectingsheetexpansion,resultinginmechanicalstress.MechanicalstressontheexistenceoftherigidjointsorP,narmiseasytofracturemayeventuallyleadtothedamageofthethermocouple,soastoshortentheservicelifeofthethermoelectricmodule.Inordertoincreasetheresistance,thethicknessofthetransitionlayerissmallerthan0.3mm;(3)thematrixmaterialischanged.Duetoitshighstrength,goodthermalconductivityandlowprice,ithasbecomeoneofthemostwidelyusedmatrixmaterials.Butthehardnessoftheceramicpieceislarge,itiseasytocauseP,Npowerarmbroken.Iftherearesomeflexibleandcansupporttheroleofnewmaterialstoreplacetheceramicpieces,throughtheflexibilityofthematrixtoalleviatethemechanicalstress,willbeabletoeffectivelysolvetheproblemofelectricalarmfracture.3.2.2environmentalfactors(1)moisture.Thereareatleastthreekindsofmaterials,thermoelectricmaterials,solderandconnectingsheetmaterials.Theingressofmoisture,inthecoldjunctionnearthecondensation,formingprimarybatteries,thusproducedtheeffectofelectrolyticcorrosionatthejoint,leadsolderresistanceincreases,finalweldingheadwascompletelydamaged.Itisbettertomakethethermoelectriccomponentsworkinvacuumortoprotecttheinsulationmaterial;(2)hightemperature.Hightemperaturecandamagetheaccelerator.Thereasonistheoxidationandsublimationofthesolder,whichacceleratesthediffusionofcopperandotherimpuritiesintothethermoelectricmaterials.Therearereportsof300K,thediffusionrateofimpuritiesis10-6cm/simpuritydiffusioncausedbymaterialSeebeckcoefficientandtheelectricalconductivitydecreasesrapidly.Atpresent,thecommonlyusedsolutionisinthecopperconnectionpieceandtheelementendsurfacenickelplating,butthenickelplatingprocessisnotideal.4conclusionsDuetoitsuniqueadvantages,thethermoelectricpowergenerationtechnologyhasshownagoodapplicationprospectinaerospaceandmilitaryfields.Atthesametime,asakindofgreenenvironmentalprotection,theapplicationofthecivilfieldinrecentyearshasdevelopedrapidly.Althoughtheefficiencyofthermoelectricpowergenerationisgenerallylowerthan10%,butwiththeelectricalresearchanddevelopmentofnewhighperformancethermoelectricmaterialsandreliableperformanceofthetemperaturedifference,temperaturedifferencepowergenerationtechnologywillbemoregreatlyplaytheadvantageoftheuseoflowgradeenergy.Accordingtotheresearchprogressofthermalpowergenerationtechnologyathomeandabroad,theresearchprogresscanbecarriedoutfromthefollowingthreeaspects:(1)theproblemoflowthermoelectricpowerefficiencyisthefirstonetobreakthroughtheimprovementoftheperformanceofthermoelectricmaterials.Doping,crystalstructure,lowdimensional,superlatticestructureandnanotechnologycanefficientlyimprovethethermoelectricfigureofmerit,andthusbecomethedevelopmentdirectionofthermoelectricmaterials;(2)byANSYSnumericalsimulationandexperimentalstudyoncombinedapproach,ofthethermoelectricelectricalparametersoptimization.Atthesametimeonthelowtemperaturesideimplementationreasonablethermalmanagement,makethetemperaturedifferencegeneratorinthematchingconditions,isalsoanimportantwaytoimprovetheefficiencyofpowergeneration;(3)temperaturedifferencepowergenerationapplicationsincreasinglywidespread,asapartofthesystem,thermoelectricitycomponentreliabilityproblemscannotbeignored.Structuralimprovementcaneffectivelyreducethemechanicalstress,someoftheauxiliarymeasurescanreducetheimpactofenvironmentalfactors,buttherearestillmanyneedstoimprovethework.温差发电技术的研究进展及现状温差发电又叫热电发电，是一种绿色环保的发电方式。温差发电技术具有结构简单，坚固耐用，无运动部件，无噪声，使用寿命长等优点。可以合理利用太阳能、地热能、工业余热废热等低品位能源转化成电能。温差发电技术的研究最早开始于20世纪40年代。由于其显著的优点，温差发电在航空、军事等领域得到了广泛的应用，美国，前苏联先后研发了数千个放射性同位素或核反应堆温差发电器用作空问、海洋装置的电源。随着化石能源的日趋枯竭，美国、日本、欧盟等发达国家更加重视温差发电技术在民用领域的研究，并取得了长足的进展。国内温差发电方面的研究，主要集中在发电器理论和热电材料制备方面的研究，旨在为温差发电器的优化提供理论指导和制备性能优良的热电材料，虽然我国是世界上最大的半导体热电器件输出国，但是在温差发电器综合设计和应用方面的研究还很欠缺，因此研究温差发电有着非常现实的意义。本文介绍了温差发电技术的原理，回顾了国内外的研究进展及现状，以常见的商用温差电组件为例，对温差发电中存在的发电效率低，温差电组件使用寿命短，可靠性不高等问题进行了分析，并提出了应对策略。随着热电材料性能的提高和温差电组件可靠性的增加，温差发电应用前景广阔。1工作原理温差发电是基于热电材料的塞贝克效应发展起来的一种发电技术，将P型和N型两种不同类型的热电材料(P型是富空穴材料，N型是富电子材料)一端相连形成一个PN结，置于高温状态，另一端形成低温，则由于热激发作用，P<N)型材料高温端空穴(电子)浓度高于低温端，因此在这种浓度梯度的驱动卜，空穴和电子就开始向低温端扩散，从而形成电动势，这样热电材料就通过高低温端问的温差完成了将高温端输入的热能直接转化成电能的过程。单独的一个PN结，可形成的电动势很小，而如果将很多这样的PN结串联起来，就可以得到足够高的电压，成为一个温差发电器厂2国内外温差发电技术的研究进展2.1国外研究进展自1821年Seebeck发现塞贝克效应以来，国外对温差发电进行了大量的研究，1947年，第一台温差发电器问世，效率仅为1.5%。1953年，Loffe院士研究小组成功研制出利用煤油灯、拖拉机热量作热源的温差发电装置，在用电困难地区作小功率电源之用。20世纪60年代，一些具有较好热电性能的材料，温差发电的研究热潮达到高峰，特别是前苏联和美国，由于国防、军事等特殊行业的推动，温差发电技术的应用发展迅速。到20世纪60年代末，前苏联先后制造了1000多个放射性同位素温差发电器（RTG)，广泛用于卫星电源、灯塔和导航标识，其平均使用寿命超过10年。美国也不甘落后，其开发的RTG最长工作时问已超30年。1961年6月美国SNAP-3A能源系统投入使用，输出功率为2.7W，发电效率5.1%。1977年发射的木星、土星探测器上使用的RTG}输出功率已达到155W。20世纪80年代初，美国又完成500-1000W军用温差发电机的研制，并于80年代末正式进入部队装备。随着能源危机和环境污染的加剧，人们开始关注温差发电在废余热利用中的价值，很多国家已将发展温差电技术列为中长期能源开发计划。日本开展了一系列以“固体废物燃烧能源回收研究计划”为题的政府计划，研究用于固体废物焚烧炉的废热发电技术，将透平机和温差发电机结合，实现不同规模垃圾焚烧热的最大利用。2003年11月美国能源部宣布资助太平洋西北国家实验室、密西根技术大学等单位，重点支持他们在高性能热电材料和应用技术方面的研究，特别是工业余热废热的利用。近年来，对低品位热源的利用成为温差发电技术研究的大方向。Maneewan等利用置于屋顶的钢板吸收太阳能集热升温与环境之问的温差发电，带动轴流风})L引导屋顶空气自然对流，从而给屋顶降温。Rida等将温差发电器热端与该国一种做饭的火炉外壁连接，冷端置于空气中，利用炉壁高温与环境的温差来发电，输出功率达4.2W。Hasebe等利用夏日路面高温做热源，热交换管为集热器，采用19组温差电组件，在热管管内液体流速为0.7L/min时，输出功率3.6WThacher等在美国能源部和纽约州能源研究开发权利机构资助下开发的汽车尾气余热发电系统，使用20组HZ-20温差电组件，热电材料为Bi-Te基材料，汽车时速112km/h时，最大温差174℃，最大输出功率255W，2006年，BSST的科学家和BMW联合宣布，商用的汽车温差发电器将于2013年投入使用。Douglas等针对热源动态变化情况，设计出多模块交互回路温差发电器，在相同热源下，输出功率最大提高25%。2.2国内研究进展国内在温差发电方面的研究起步相对较晚，主要集中在理论和热电材料的制备等方面的研究。陈金灿课题组从20世纪80年代开始对温差发电器的基础理论进行研究，对温差发电器的性能进行优化分析，得到很多有意义的成果[no。屈健等李玉东等提出从火用的角度对低温差下发电器的工作性能进行分析。贾磊等提出低温及大温差工况下汤姆逊热对输出功率的影响不可忽略的观点。贾阳等建立温差发电器热电祸合分析模型，以数值计算的方法分析了热电材料物性参数及其变化对发电器工作特性的影响，得出结论，材料的导热系数、电阻率及塞贝克系数对发电器转换效率的影响均为非线性，其中导热系数的影响最明显。德鹏等分析了温差发电器的热环境、回路中负载电阻等参数及温差电单体对的连接方式对发电器工作性能的影响，得出提高温差发电器热端加热热流或增加冷端的换热系数均能提高发电器的输出功率及热电转换效率的结论。苏景芳研究了系统与环境，系统与系统之问的热流关系，对系统的性能特性作出优化，建立温差发电器优化设计模型，同时以VB6.0(Mi-crosoftVisualBasic6.0)语言作为开发工具，ActiveX数据对象访问数据库，编写了温差发电器设计软件。钱卫强通过对低品位热源半导体小温差发电器性能的研究，总结了电动势、内阻及输功率等参数随外电路、温度、发电组件几何尺寸等因素的变化规律，另外研究了串、并联情况下温差电组件的性能。李伟江从非平衡热力学角度出发，建立单层多电偶发电器在低温差下稳定工作的模型。研究温差发电器在内部结构和外部换热条件变化情况下的运行规律，与实验相结合，得出最佳匹配系数下，输出功率和发电效率均随最大温差近似呈线性变化，同时指出解决发电效率低的问题根本上依靠的是材料性能的改善。刚现东理论分析和实验研究相结合，通过模拟坦克排气筒附近区域制冷状况，由降温情况评估红外隐身效果，得出以坦克尾气余热为热源将温差电技术应用于坦克红外隐身完全可行的结论。3.1发电效率目前，温差发电的效率一般为5%-7%，远低于火力发电的40%。最主要的原因是热电材料性能不理想，另一方面是发电器的匹配问题厂。3.1.1热电材料的限制热电材料作为热电器件的核心部分，性能的好坏直接决定器件效能的优劣。优值ZT是衡量热电材料性能最重要的参数。ZT值越高，材料的热电性能越好，能量转换效率越高。Bi2T3;室温下ZT值1左右，是使用最广泛的热电材料。但是以;Bi2T3材料制作的温差发电器发电效率依然低于10％。如果能把材料的ZT值提高到3左右，温差发电将可以与传统的发电方式相媲美。为此，人们积极寻找和开发具有较高优值的新型热电材料，目前的研究热点有:钻基氧化物热电材料、准晶体材料、超晶格薄膜热电材料、纳米热电材料等。Terasaki等首次发现NaCo2O4单晶在室温卜具有较高的Seebeck系数，较低的电阻率和较低的热导率，为此引起人们的关注，但是NaCo2O4在空气中易潮解且超过1073K时易挥发，所以人们把目光转向另一种钻基氧化物Ca-Co-O系。Funahashi的研究预测:Ca2Co2O5在T≥873K时，ZT=1.2一2.7。准晶体热电材料1984年由Shechtman等首次发现，近年来引起关注。这种材料热力学稳定性好，电阻率高，具有负的导热系数，故导电性能好，导热性能低。有研究预言室温下可得到ZT=1.6的准晶体热电材料。超晶格是由两种材料的半导体单晶薄膜周期性交替生长形成的多层异质结构，每层薄膜含几个以至几}一个原子层。由于这种特殊结构，半导体超晶格中的电子(或空穴)能量将出现新的量子化，进而引起态密度的提高，因此超晶格材料具有许多新的特性。Venkatasubramanian等采用金属有机化合物气相沉积(MOCVE)法将Bi-Te基合金制备成超晶格薄膜,300K时ZT值达到2.4。Dresselhaus对Bi纳米线及量子阱系统的大量研究后预言，通过超晶格量子限制效应可以得到ZT值大于3的材料。纳米热电材料是热电材料的另一研究热点，浙江大学在此领域成果卓著。赵新兵等研究发现传统Bi-Te基热电材料中添加15%的含有Bi2T3;纳米管粉末，可以使材料的热电性能提高20%左右。Cao等采用水热合成法热压后得到ZT=1.28的(Bi,Sb)2Te3;纳米热电材料。ZHAO等通过纳米粉末掺杂，制得ZT值均超过1.5的Bi2Te3-Sb2Te3和GeTe-AgSbTe2纳米结构材料。3.1.2匹配问题温差发电器的输出功率和发电效率与高温端温度(Th）。低温端温度(Tc)，温差发电回路电流(I)，负载电阻(R)，发电器内阻(r)等因素密切相关。在不同条件下，温差发电器的性能差别较大。屈健等应用有限时问热力学理论对半导体温差发电器的工作性能进行了分析，得到温差发电存在最佳参数工作区的结论。潘玉灼等采用非平衡态热力学优化控制理论分析温差电模型，数值模拟结果表明:最匹配参数工作条件下输出功率和发电效率可分别提高39%和20%发电器热设计也是影响发电效率的重要因素。为了保持较高的温差，往往在发电器低温端增加散热装置，以使热量及时散失。Chein研究指出当器件热阻大于散热器最大热阻时，散热器将小能够散走器件产生的热量，因此与温差发电器匹配的冷端散热方式也是影响发电器性能的重要因素。目前主要的散热方式有:风冷、液冷和相变散热。风冷又分为自然风冷和强制风冷。自然风冷换热器是一定形状的翅片散热器。热阻大小与翅片密度、散热器面积直接相关。目前温差发电器中应用较多的是强制风冷，散热器(如热沉)与风扇结合，低温端热量传导到更大面积的翅片上，借助强制散热将热量散失到空气中。热阻取决于风速，风速越大，热阻越小。强制风冷可有效地提高散热器的对流换热系数，减小散热面积，而且结构简单，易于实现，因而应用广泛。因液体的单位热容较气体大，因而液冷比风冷有更好的冷却效果，研究表明液冷换热系数比自然风冷散热大100-1000倍，热阻大小主要与液体的流速有关，流速越大，热阻越低。目前应用的液体散热方式主要有液体喷射冷却、微通道液体冷却和宏观水冷管路冷却。相变散热是利用相变材料相态变化时吸收热量来散热。这种散热方式适用于问歇式工作场合，目前研究最多的是带相变热虹吸管散热。Esartet的研究结果表明带相变热虹吸管可明显提高热流在传热面的均匀性，减小热阻，散热较好。3.2可靠性问题3.2.1和机械应力的存在以常见的三明治式温差电组件为例，要达到较高的发电效率，通常要求发电组件冷热端之问形成较大温差，这将造成冷端连接片收缩或热端连接片膨胀，从而产生机械应力。机械应力的存在使得刚性的接头或P,N电臂很容易断裂，最终可能导致温差电偶的损坏，从而缩短了温差电组件的使用寿命。为了小增加电阻，要求过渡层厚度小超过0.3mm;(3)改变基体材料。金属化陶瓷片由于强度高、导热性好、价格低廉，因而成为目前使用最广泛的基体材料。但是陶瓷片硬度大，极易造成P,N电臂折断。如果采用有一定柔性而又能起支撑作用的新材料来代替陶瓷片，通过基体的柔性来缓解机械应力，将能有效地解决电臂断裂的问题。3.2.2环境因索湿气。焊接处至少存在热电材料、焊料和连接片材料三种物质。湿气进入，在冷接头附近结露，