Preparation And Properties Research Of Erythritol Based Composite Phase Change Materials

Phase change materials(PCMs)as a new kind of thermal energy storage materials that have been widely studied in recent years.It can be applied in lots of fields such as solar thermal application,peak load shifting,waste heat recovery and thermal management of spacecrafts and cells,etc.Erythritol(ET)is a medium temperature organic solid-liquid PCM that possesses the merits of high phase change enthalpy(△H,～340 J·g-1),nontoxicity,good thermal stability,etc.However,ET also exhibits some disadvantages such as severe supercooling and low thermal conductivity.This thesis is devoted to reduce the supercooling degree(△T)of ET,improve its latent heat releasing stability and thus optimize its application.Besides,the thermal conductivity of ET was also improved by doping graphene oxide(GO),which is further helpful for its application.The main research contents of this thesis can be divided into five sections.1.Preparation and characterization of ET/nucleating agent composite PCMs.Five kinds of nanoparticles were selected as nucleating agents and ET/nucleating agents composite PCMs were prepared in ethanol/aqueous solution.The effects of the selected nucleating agents and their loading on the △T of ET were investigated.The results showed that SiO2 nanoparticles(nano-SiO2)exhibited the best result on reducing the of ET.Moreover,the △T was initially decreased and then increased ad the loading of the nano-SiO2 was increased.When the loading of the nano-SiO2 was 2.0wt.%,the lowest △T(67.12℃)was obtained,which is 33.53%lower than that of pristine ET.Meanwhile,the melting enthalpy(△Hm)and the crystallizing enthalpy(△Hc)of the composite PCM containing 2.0wt.%SiO2 nanoparticles were 323.50 J·g-1 and 214.60 J·g-1,respectively.2.Preparation and characterization of ET/thickener composite PCMs.We selected three kinds of thickeners and a series of ET/thickener composite PCMs were prepared in ethanol/aqueous solution.The effects of the selected thickeners and their loading on the properties of ET were then investigated.The results revealed that the best results on reducing the △T of ET could be obtained when the loading carboxymethylcellulose(CMC)was 2.0wt.%.The △T of the ET/CMC composite PCM with 2.0wt.%CMC was 76.97℃,while the △Hm and △Hc were 300.80 J·g-1 and 209.00 J·g-1,respectively.3.Preparation and characterization of ET/nucleating agent/thickener composite PCMs.In order to investigate the synergistic effects of the nucleating agents and the thickeners on the properties of ET,a series of ET/nucleating agent/thickener composite PCMs were prepared and characterized.The results showed that the ET/nano-SiO2/CMC composite containing 2.0wt.%nano-Si02 and 2.0wt.%CMC exhibited the AT of 49.58℃,which was 50.90%lower than that of pristine ET.The result implied that the nano-SiO2 and CMC exhibited obvious synergistic effect on reducing the △T of ET.Moreover,the composite PCM possessed high AHm and △Hc,which were 314.60 J·g’1 and 232.30 J·g-1,respectively.In addition,the composite PCM exhibited good stability over the experiment temperature range.4.Preparation and characterization of ET/SiO2 form-stable PCMs.A series of ET/SiO2 form-stable PCMs were prepared via a one-pot sol-gel method in which the acid catalyzed hydration of tetraethyl orthosilicate(TEOS)was carried out in a saturated ET aqueous solution,which was followed by drying of the mixture.The characterization results of the prepared form-stable PCMs showed that the AT was 53.360 C,which was 47.16%lower than that of pristine ET.However,the AHm(204.10 J·g-1)and △Hc(156.60 J·g-1)of the prepared form-stable PCM were relatively low.5.Preparation and characterization of ET/SiO2/GO form-stable PCMs.GO was selected as nucleating agent and thermal conductive filler,and a series of ET/SiO2/GO composite form-stable PCMs were prepared via a one-pot sol-gel method in which GO was dispersed in the saturated ET aqueous solution and then the basic-catalyzed hydration of TEOS was carried out in the solution.Investigation on the properties of the prepared form-stable PCMs revealed that the △T of ET was greatly suppressed by GO and SiO2.The AT was only 14.20°C,which is 85.90%lower than that of pristine ET,when the loading of ET was 85.0wt.%and the loading of GO was 6.0wt.%.Moreover,the composite form-stable PCM possessed high△Hm(223.60 J·g-1)and △Hc(216.80 J·g-1).It implied that the prepared form-stable PCM possesses excellent thermal energy storage/release properties,and can be applied in solar thermal application and waste heat recovery.