dsc測量比熱容課件

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)定義：在程序控制溫度下，測量物質(zhì)與參比物之間的能量差隨溫度變化關(guān)系的一種技術(shù)。DSC曲線峰包圍的面積正比于熱焓的變化可以測定多種熱力學和動力學參數(shù)，例如比熱容、反應熱、轉(zhuǎn)變熱、相圖、反應速率、結(jié)晶速率、高聚物結(jié)晶度、樣品純度等。該法使用溫度范圍寬（-175~725℃）、分辨率高、試樣用量少。適用于無機物、有機化合物及藥物分析。差示掃描量熱法（DSC）

（DifferentialScanningCalorimetry）

采用試樣和一標準物質(zhì)在相同條件下進行掃描，然后量出二者的縱坐標進行計算。要求標準物質(zhì)在所測溫度范圍內(nèi)沒有發(fā)生物理化學變化，且比熱容已知。常用的標準物質(zhì)是藍寶石。具體作法是在DSC內(nèi)先用兩個空樣品皿，以一定的升溫速度作一條基線，然后放入藍寶石樣品在相同條件下作一條DSC曲線，最后在同樣條件下作未知試樣的DSC曲線，如圖二、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.