Preparation And Performances Of Fatty Acids Composite Phase Change Materials For Thermal Storage

Fatty acids can meet the thermal storage property and thermal stability requirements of ideal phase change materials.However,the leakage in the melted state and poor thermal conductivity are characterized as two key disadvantages.In this study,expanded vermiculite was modified to improve the adsorption property and thermal conductivity,and then used as the supporting matrix of fatty acids to prepare composite phase change materials by vacuum impregnation method.The main works were as follows:(1)Myristic-stearic acid(MA-SA)/expanded vermiculite/graphite composite phase change materials:The expanded vermiculite(EV)was treated with 8mol/L nitric acid(aEV8)to greatly improve the adsorption capacity of EV.In order to improve the thermal conduction property,5wt%graphite was introduced to the aEV8(aEV8G).The aEV8G was used as the optimum MA-SA supporting matrix.The thermal conductivity of the MA-SA/aEV8G was 0.742W/mK,which was 177.90%and 44.36%higher than that of MA-SA and MA-SA/EV,respectively.The latent heats of the MA-SA/aEV8G were 98.8J/g at the melting temperature of 44.3? and 94.6J/g at the freezing temperature of 43,1?,which were also higher than those of MA-SA/EV.Therefore,the prepared MA-SA/aEV8G is a preferential potential PCM for solar heating applications.(2)Capric-myristic-stearic acid(CA-MA-SA)/expanded vermiculite/intercalation carbon composite phase change materials:The expanded vermiculite/carbon composite(EVC),obtained by in-situ carbonizing cetyl trimethyl ammonium bromide in the layer of expanded vermiculite,was treated with nitric acid(aEVC)to be used as the CA-MA-SA supporting matrix.The results showed that the thermal conductivity of CA-MA-SA/aEVC was greatly enhanced by introducing carbon and the CA-MA-SA adsorption capacity was improved by the acid-treatment of EVC.The thermal conductivity of CA-MA-SA/aEVC was 0.667W/mK,which was 31.6%higher than that of CA-MA-SA/expanded vermiculite(EV).The latent heats of the CA-MA-SA/aEVC were 86.4J/g at the melting temperature of 22.9? and 80.4J/g at the freezing temperature of 21.0?,which were also greatly higher than those of CA-MA-SA/EV.Thus,the prepared CA-MA-SA/aEVC composite PCM is a promising material for the building energy efficiency applications.(3)Stearic acid(SA)/expanded vermiculite/TiO2 composite phase change materials:The expanded vermiculite loaded with titanium dioxide and treated with nitric acid(aEVT)was used as the optimum SA supporting matrix.The thermal conductivity and latent heat of the SA/aEVT composite PCM were enhanced simultaneously compared with those of SA/expanded vermiculite(EV)and SA/expanded vermiculite with acid treatment(aEV)composite PCMs.The thermal conductivity of the SA/aEVT was 0.576W/mK,which was 126.8%,11.4%and 20.3%higher than those of SA,SA/EV and SA/aEV,respectively.The latent heats of SA/aEVT were 146.8J/g at the melting temperature of 65.9? and 141.7J/g at the freezing temperature of 63.4? which were also higher than those of SA/EV and SA/aEV.Thus,the prepared SA/aEVT is a promising PCM for latent heat storage systems.(4)Lauric-myristic-stearic acid(LA-MA-SA)/expanded vermiculite/Al2O3 composite phase change materials:The expanded vermiculite(EV)was treated with nitric acid(aEV)to improve the adsorption capacity of EV.The Al2O3 nano-particles,with high thermal conductivity and surface area,were loaded on aEV(aEVA)prepared by in situ reduction of a metal salt solution.The aEVA was used as the LA-MA-SA supporting matrix.The thermal conductivity of LA-MA-SA/aEVA was 0.671W/mK,which was 156.1%,30.8%and 37.5%higher than that of LA-MA-SA,LA-MA-SA/EV and LA-MA-SA/aEV,respectively.The latent heats of LA-MA-SA/aEVA were 113.7J/g at the melting temperature of 28.6? and 108.5J/g at the freezing temperature of 26.9 ?,which were also higher than those of LA-MA-SA/EV and LA-MA-SA/aEV.Therefore,LA-MA-SA/aEVA is a preferential potential thermal energy material for the building energy efficiency applications.