dsc测量比热容.ppt

A,1,Newproposedmethodologyforspecificheatcapacitydeterminationofmaterials,forthermalenergystorage(TES)byDSC,Abstract,1.Introduction,2.Materials,3.Methodology,4.Results,5.Conlusions,abstract,Thisstudypresentsamethodologytodeterminethespecificheatcapacity(Cp)ofmaterialsforthermalenergystorage(TES)byDSC.ThreedifferentDSCmethodsareconsideredtobeappliedinthemethodology,andareexplainedandcomparedinthisstudyinordertoselectthemostproperoneforCpdetermination.Toperformthisstudy,theCpofthreematerialscommonlyusedinsensibleTESsystems,slate,water,andpotassiumnitrate(KNO3),isdetermined.,一、introduction,lackoffossilenergeticresourcesitspriceneedtodecreaseCO2emissionsleadtodedevelopnewenergysystemsabletotakeprofitofrenewableenergyandbeenvironmentallyfriendlyandlessexpensive,TESsystemsareapossiblesolutionSblem:asthehoursofmaximumenergydemandmatchwiththehoursofnosolarirradiation,withtheaimtofillthisexistingenergysupplygap,TESsystemsarepresentedasthesolutiontostoretheenergyanduseitanytime,TEStechnologiessensibleheatstoragetheprocessbywhichtheheatisaccumulatedduetotheincreaseofthematerialtemperaturewithoutexperimentingstructuralchanges,nophasechangelatentheatstoragephasechange,thermochemicalenergymaterialselectionAhighstoragecapacityTherefore,needahighspecificheatcapacity.,(1),定义：在程序控制温度下，测量物质与参比物之间的能量差随温度变化关系的一种技术。DSC曲线峰包围的面积正比于热焓的变化可以测定多种热力学和动力学参数，例如比热容、反应热、转变热、相图、反应速率、结晶速率、高聚物结晶度、样品纯度等。该法使用温度范围宽（-175725）、分辨率高、试样用量少。适用于无机物、有机化合物及药物分析。,差示扫描量热法（DSC）（DifferentialScanningCalorimetry）,采用试样和一标准物质在相同条件下进行扫描，然后量出二者的纵坐标进行计算。要求标准物质在所测温度范围内没有发生物理化学变化，且比热容已知。常用的标准物质是蓝宝石。具体作法是在DSC内先用两个空样品皿，以一定的升温速度作一条基线，然后放入蓝宝石样品在相同条件下作一条DSC曲线，最后在同样条件下作未知试样的DSC曲线，如图,threeDSCmethodsforCpmeasurementThedynamicmethodhastraditionallybeenusedtomeasurePCMlatentheatbutalsoforCpmeasurementsapplyinghighheatingratesinthetemperaturerangeofstudyTheareasmethodisbasedontheCpvalue,thus,howmuchheatfluxisneededtoheatupamaterialfortemperatureincrease,andconsistsofconsecutiveisothermalstagesdiffering1withnoheatingsegmentsamidTheisostepmethodisanintermediatebetweenthesetwo,asitisasuccessionofdynamicmethodsappliedtoheatupthematerialjust1betweenisothermalsegments.Thismethodhasbeentestedinglasstransitionpharmaceuticalstudieswithgoodresultsobtained,butithasnotbeenusedforTESmaterialsCpdetermination,therebyitsselectionforthisstudy,A,9,二、Materials,Toensuretheperformanceofthemethodologyinarepresentativevarietyofmaterialphaseformsandchemicalstructures,threedifferentmaterialswidelyusedinsensibleheatstoragesystemshavebeenchosentoperformthisstudy.Water.Itsthermalpropertiesarewellknown,andtherefore,thesevaluescanbeusedasareferencetoseetheapproachonthemeasurementseachmethodhas.CommercialBi-distillatedwaterfromPanreachasbeenusedtoperformtheexperimentsSlate.Itisawidelyusedconstructionmaterialanditsperformancedependsonitsspecificheatcapacity,thereforeauthorsfinditaninterestingmaterialtobetested.TheslatesamplesusedinthisstudyweretakenfromaquarryintheCatalanPyrenees.Potassiumnitrate.Itisaninorganicsaltmainlyusedasmoltensaltinconcentratedsolarpowerplants(CSPPlants).Ithashighmeltingpoint(320)and,asallinorganicsalts,acomplexchemicalstructure,andthatiswhyitisalsofoundtobeusefulforthispaperspurpose.ItisimportanttoremarkthatthismaterialselectionrespondstotheneedtotestthemethodologyandnottotieittoaconcretematerialtypeoraspecificTESapplication.Therefore,materialsusedindifferentTESsystemsandwithwhichauthorscommonlyworkhavebeenselected.,determinedbydifferentialscanningcalorimetry(DSC)Standard40uLaluminiumcruciblesweighwithaanalyticalbalancewithaprecisionof0.01mg.Theproceduretodeterminethespecificheatcapacityofamaterialconsistsofthreedifferentmeasurements,alldoneunderthesameconditions,thus,usingthesameDSCmethod:Blankmeasurement.Itisnecessarytorunanexperimentwithanemptycrucibletomeasuretheheatfluxthatcorrespondstothecruciblematerialinordertosubtractthissignalandconsideronlythesapphireandmaterialsampleones.Sapphiremeasurement.Sapphireisthematerialusedasreferenceasitsspecificheatcapacityiswellknownateverytemperatureanditssignalishugelystableovertemperature,datanecessaryforthematerialsCpcalculation.Materialmeasurement.NeededtodeterminetheCpvalueofthematerialunderstudy.,三、Methodology,mW,K/S,(2),Thesensitivityoftheanalysisistiedtotheheatingrateandthesamplemass.literaturestudiesfoundhighheatingratesofabout1020K/minaredesiredEq.(2)shows,minorsamplemassesareneeded.TheCpwasmeasuredbetween15and16,2526and3536forallthematerialsunderstudy.Thesemeasurementrangeswereselectedinordertoensurethatwaterwasinliquidstateandtobeabletotakethecertainknownwater4.18J/gCpvalueat25asareferencetoevaluateeachmethodperformance.,3.1.DSCmeasurementmethods3.1.1.DynamicmethodItisatemperaturecontrolledmethodthatachievesthethermalequilibriumbeforeandafteracontrolledheatingsegment,itconsistsofthreesegments.1015mintohomogenizethematerialtemperaturehighheatingrateanotherisothermalstageagainfor1015minthelowerandhighertemperaturesofthemethodcanbe150,（3）,A,12,Similartothepreviousexplaineddynamicmethod,theisostepmethodThismethodusesEq.(3)tocalculatetheCpofthematerialalongeachheatingsegment.,3.1.2.isostepmethod,3.1.3.AreasmethodTheareasmethodconsistsofconsecutiveisothermalsegmentswithnoheatingstagesamid.Eachofthepeakscorrespondstoeverytemperaturestepofthemethod.Thetemperaturedifferencebetweenisothermsisof1.,whereAsJ/gistheintegratedpeakareaforthesapphirecurve,Inthisstudy,resultsaregivenwithanerrorof3%,includingbothequipmentandcalculationerrors.Thedynamicmethodgivesacontinuoussignalalongthewholetemperaturestudyrange,asshowninredThreedifferentcontinuoussignalsareobtainedwiththeisostepmethod,oneforeachheatingsegmentforthe1516C,2526Cand3536Csteps.However,asthemeasurementtemperaturerangeisofjust1Candthematerialisheatedatareallyfastrate,四、results,thethreesignalsarereallysteepandnocleartendencycanbeseenintheresults,factthatalreadyshowsthelowsensitivitythismethodhasforCpcalculation.Nevertheless,andinordertocomparethemethods,anaveragevalueofthemostconstantpartsofthesethreesignalsispresentedinthegraphics.Contrary,theareasmethodprovidesjustthreepoints,oneforeachtemperatureincrementbetweentheisothermalsegments,hence,oneat16C,oneat26Candoneat36C.,4.1water,areasmethodgetscloservaluestothetheoreticaivaluesThedynamicmethodinconsistentvaluesarefoundinthebeginingandtheend,thatindicatessensitivityproblemsinthesetwomeasurementparts.theisostepmethodaretheaverageofthemostconstantpartsoftheobtainedsignal,beingthestandarddeviationforwaterof0.08J/g.,Thesensitivityproblems.Duetotheabrupttemperaturechangeonbothinitialandendpoints,theDSCtemperaturesensorcannotreactfastenoughtoreadtherealtemperature.Thisfacthasgreatersignificanceintheisostepmethodresultsduetothehigherrelationbetweenheatingrateandtemperatureincrease.,A,16,resultsshowthattheareasmethodisthemethodthatprovidesCpclosetothetheoreticalrangedynamicmethodtheisostepmethod,withastandarddeviationof0.03J/g.mostinconsistent,4.2.slate,4.3.potassiumnitrate,sameconditionsamereason,bothdynamicandisostepmethodmeasurementsarelimitedbythehighheatingratesapplied,paringthethreematerialresultsanaly