dsc测量比热容课件

Newproposedmethodologyforspecificheatcapacitydeterminationofmaterialsforthermalenergystorage(TES)byDSCAbstract1.Introduction2.Materials3.Methodology4.Results5.ConlusionsabstractThisstudypresentsamethodologytodeterminethespecificheatcapacity(Cp)ofmaterialsforthermalenergystorage(TES)byDSC.ThreedifferentDSCmethodsareconsideredtobeappliedinthemethodology,andareexplainedandcomparedinthisstudyinordertoselectthemostproperoneforCpdetermination.Toperformthisstudy,theCpofthreematerialscommonlyusedinsensibleTESsystems,slate,water,andpotassiumnitrate(KNO3),isdetermined.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（-175~725℃）、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，如图二、MaterialsToensuretheperformanceofthemethodologyinarepresentativevarietyofmaterialphaseformsandchemicalstructures,threedifferentmaterialswidelyusedinsensibleheatstoragesystemshavebeenchosentoperformthisstudy.Water.Itsthermalpropertiesarewellknown,andtherefore,thesevaluescanbeusedasareferencetoseetheapproachonthemeasurementseachmethodhas.CommercialBi-distillatedwaterfromPanreachasbeenusedtoperformtheexperimentsSlate.Itisawidelyusedconstructionmaterialanditsperformancedependsonitsspecificheatcapacity,thereforeauthorsfinditaninterestingmaterialtobetested.TheslatesamplesusedinthisstudyweretakenfromaquarryintheCatalanPyrenees.Potassiumnitrate.Itisaninorganicsaltmainlyusedasmoltensaltinconcentratedsolarpowerplants(CSPPlants).Ithashighmeltingpoint(320℃)and,asallinorganicsalts,acomplexchemicalstructure,andthatiswhyitisalsofoundtobeusefulforthispaper’spurpose.ItisimportanttoremarkthatthismaterialselectionrespondstotheneedtotestthemethodologyandnottotieittoaconcretematerialtypeoraspecificTESapplication.Therefore,materialsusedindifferentTESsystemsandwithwhichauthorscommonlyworkhavebeenselected.determinedbydifferentialscanningcalorimetry(DSC)Standard40uLaluminiumcruciblesweighwithaanalyticalbalancewithaprecisionof0.01mg.Theproceduretodeterminethespecificheatcapacityofamaterialconsistsofthreedifferentmeasurements,alldoneunderthesameconditions,thus,usingthesameDSCmethod:Blankmeasurement.Itisnecessarytorunanexperimentwithanemptycrucibletomeasuretheheatfluxthatcorrespondstothecruciblematerialinordertosubtractthissignalandconsideronlythesapphireandmaterialsampleones.Sapphiremeasurement.Sapphireisthematerialusedasreferenceasitsspecificheatcapacityiswellknownateverytemperatureanditssignalishugelystableovertemperature,datanecessaryforthematerial’sCpcalculation.Materialmeasurement.NeededtodeterminetheCpvalueofthematerialunderstudy.三、MethodologymWK/S(2)Thesensitivityoftheanalysisistiedtotheheatingrateandthesamplemass.

literaturestudiesfoundhighheatingratesofabout10–20K/minaredesiredEq.(2)shows,minorsamplemassesareneeded.TheCpwasmeasuredbetween15and16℃,25–26℃and35–36℃forallthematerialsunderstudy.Thesemeasurementrangeswereselectedinordertoensurethatwaterwasinliquidstateandtobeabletotakethecertainknownwater4.18J/g℃Cpvalueat25℃asareferencetoevaluateeachmethodperformance.3.1.DSCmeasurementmethods3.1.1.DynamicmethodItisatemperaturecontrolledmethodthatachievesthethermalequilibriumbeforeandafteracontrolledheatingsegment,itconsistsofthreesegments.10–15mintohomogenizethematerialtemperaturehighheatingrateanotherisothermalstageagainfor10–15minthelowerandhighertemperaturesofthemethodcanbe150℃（3）3..1.3.AreasmethodTheareasmethodconsistsofconsecutiveisothermalsegmentswithnoheatingstagesamid.Eachofthepeakscorrespondstoeverytemperaturestepofthemethod.Thetemperaturedifferencebetweenisothermsisof1℃.whereAs[J/g]istheintegratedpeakareaforthesapphirecurveInthisstudy,resultsaregivenwithanerrorof3%,includingbothequipmentandcalculationerrors.Thedynamicmethod

givesacontinuoussignalalongthewholetemperaturestudyrange,asshowninredThreedifferentcontinuoussignalsareobtainedwiththeisostepmethod,oneforeachheatingsegmentforthe15–16C,25–26Cand35–36Csteps.However,asthemeasurementtemperaturerangeisofjust1Candthematerialisheatedatareallyfastrate,四、resultsthethreesignalsarereallysteepandnocleartendencycanbeseenintheresults,factthatalreadyshowsthelowsensitivitythismethodhasforCpcalculation.Nevertheless,andinordertocomparethemethods,anaveragevalueofthemostconstantpartsofthesethreesignalsispresentedinthegraphics.Contrary,theareasmethodprovidesjustthreepoints,oneforeachtemperatureincrementbetweentheisothermalsegments,hence,oneat16C,oneat26Candoneat36C.4.1waterareasmethodgetscloservaluestothetheoreticaivaluesThedynamicmethodinconsistentvaluesarefoundinthebeginingandtheend,thatindicatessensitivityproblemsinthesetwomeasurementparts.theisostepmethodaretheaverageofthemostconstantpartsoftheobtainedsignal,beingthestandarddeviationforwaterof0.08J/g℃.Thesensitivityproblems.Duetotheabrupttemperaturechangeonbothinitialandendpoints,theDSCtemperaturesensorcannotreactfastenoughtoreadtherealtemperature.Thisfacthasgreatersignificanceintheisostepmethodresultsduetothehigherrelationbetweenheatingrateandtemperatureincrease.154.3.potassiumnitratesameconditionsamereasonbothdynamicandisostepmethodmeasurementsarelimitedbythehighheatingratesapplied,paringthethreematerialresultsanalysis,atthispointitisclearthattheareasmethodis,byfar,thebestmethodappliedinthisstudytodeterminethespecificheatcapacityofamaterial.4.4.