| Crystal hydrous salt is one of the most important phase change thermal storage materials with a melting point range from 0 to 120 oC.It has many advantages such has high thermal storage density,small change in phase change volume,great coefficient of thermal conductivity,extensive sources and low cost.Ba?OH?2·8H2O is a typical one of crystal hydrous salt,which has all the advantages mentioned above and is almost the best known crystal hydrous salt that being with the largest heat storage density?582 MJ/m3?so far now.It could be widely used in the fields of household and industrial heating,waste heat recovery for industry,hot water for life and heat rejection for electronic elements.Therefore,it is a phase change material with great potential and vast application prospects for heat storage.However,there are few systematic studies and analysis reports on Ba?OH?2·8H2O PCM at home and abroad and there is no industrial application for it until now.From performance requirements of PCM for their practical application in various fields,the paper mainly studied and discussed the dewatering process of Ba?OH?2·8H2O when heating,its improvement on heat storage and thermal conductivity through theoretical analysis and related analytical test.In order to find out the phase change process of Ba?OH?2·8H2O in heating and improve the heat storage performance.The DSC-TGA curve for Ba?OH?2·8H2O at 25500?was obtained by differential scanning calorimetry and thermogravimetric synthesis analyzer firstly.From the TGA curve,we got the amount of crystal water actually contained in experimental Ba?OH?2·8H2O samples by its proportion.Meanwhile,the detailed dehydration situation during the heating process was further analyzed according to the DSC curve.We got the actual melting point and latent heat of phase change for Ba?OH?2·8H2O sample by its DSC curve at the range of 25100?.In addition,we calculated and analyzed balanced data for thermodynamics during the process of heating up and dehydration in accordance with related theory of thermodynamics,and the process of melting and dehydration was verified theoretically.In addition,the effects of Ba?OH?2·8H2O heat storage performance,addition of nucleating agent and thickening agent were investigated in this paper.We conducted 100 melting-solidification thermal cycling tests on Ba?OH?2·8H2O crystal hydrous salt PCM,studied Ba?OH?2·8H2O samples change in melting,freezing point,latent heat of phase change and phase composition before and after 100 thermal cyclings by the time experimental curve during heating up and cooling,DSC and XRD analysis,furthermore,we comprehensively analyzed the thermal physical properties,supercooling property and thermal cycling stability of Ba?OH?2·8H2O.Furthermore,we tried to restrain the supercooling phenomenon of Ba?OH?2·8H2O and improve its cycling stability by adding different additives and finally found that BaCl2·2H2O and CMC could be used as effective nucleating agent and thickening agent respectively for Ba?OH?2·8H2O PCM.When the ratio of them is 99:1:1,the composite PCM has effectively eliminated the supercooling degree and the latent heat attenuation of phase change is less than 1%after 100 melting-solidification thermal cycling tests.Finally,we prepared composite PCM with excellent thermal conductivity by adding graphene nanoplatelets into Ba?OH?2·8H2O,made melting-solidification thermal cycling experiments and discussed the effects of graphene nanoplatelets on heat conductivity and heat storage performance of Ba?OH?2·8H2O by using heating and cooling temperature-time curve,SEM,thermal conductivity test and differential scanning calorimetry analysis and test.The thermal conductivity growth rate for Ba?OH?2·8H2O composite phase change material with 1.5wt%graphene nanoplatelets is 197.6%,which has a high cost performance.Moreover,Ba?OH?2·8H2O is easy to crystallize on the surface of graphene nanoplatelets when cooling,which can effectively reduce the supercooling degree of Ba?OH?2·8H2O.This study laid a excellent foundation for further research and application of Ba?OH?2·8H2O phase change material. |
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