Research Of Expanded Graphite Composite Inorganic Phase Change Materials For Energy Storage

Low-temperature solid-liquid phase change materials are currently a research hot spot in the field of thermal energy storage.They have a high latent heat at the phase change temperature,which can effectively perform heat storage and release behavior within the phase change temperature range and adjust the temperature of the corresponding environment or equipment.They have great application prospects in the fields of building energy conservation,thermal insulation fabrics,cold chain transportation,passive thermal management and reduction of infrared radiation.Nowadays,there are more researches on the use of porous matrix to encapsulate phase change materials in order to solve the restriction of liquid flow.There are some studies on the combination of different types of packaging materials and phase change materials.Compared with organic phase change materials,hydrated salt phase change materials have a higher enthalpy and have great development potential.Among packaging materials,expanded graphite is a material with high thermal conductivity,high porosity and low price.Aiming to solve the problem of incompatibility between the hydrophobicity of expanded graphite and hydrated salt,the methods of silica loading and surfactant modification were used to improve the hydrophilicity of the matrix.Combined with the thermal properties,morphology,structure and cycle performance of the composite phase change materials prepared,the influence of the hydrophilicity of the matrix on the encapsulation of hydrated salt,the surfactant addition on the heat storage capacity of composite phase change materials,and the properties of surfactants on the latent heat of hydrated salt crystals were studied.In this paper,silica particles and colloidal silica particles are formed in the expanded graphite by adjusting the p H,and the heat storage capacities of the composite phase change materials prepared are 224 J/g and 174 J/g,respectively.Dodecyl trimethyl ammonium bromide,cetyl trimethyl ammonium bromide,cetyl trimethyl ammonium chloride and sodium lauryl sulfate are used as modifiers.The composite phase change material modified by dodecyl trimethyl ammonium bromide has a maximum initial heat storage capacity of 258 J/g,and a maximum heat storage capacity of 230 J/g after 500 cycles.The maximum initial heat storage capacity of the composite phase change material modified by cetyl trimethyl ammonium bromide is 261 J/g,and the maximum heat storage capacity after 500 cycles is 267 J/g.The cetyl trimethyl ammonium chloride modified expanded graphite matrix can promote the increase of the enthalpy of disodium hydrogen phosphate dodecahydrate.The initial heat storage capacity of the composite phase change storage material is up to 299 J/g.After 500 cycles,the heat storage capacity of the composite phase change material can reach up to 300 J/g.The composite phase change material modified by sodium lauryl sulfate has a maximum initial heat storage capacity of 265 J/g,and a maximum heat storage capacity of 259 J/g after 500 cycles.The optimal addition amount of different surfactants is different,and the crystal structure of disodium hydrogen phosphate dodecahydrate will change at a higher amount of surfactant addition.In general,cetyl trimethyl ammonium chloride modified expanded graphite material is a good encapsulation matrix for hydrated salt phase change materials.