Construction And Performance Regulation Of Diatomite-based Composite Phase Change Materials For Thermal Energy Storage

Phase change thermal storage technology has been applied in the fields of solar thermal utilization,waste heat recovery,and building energy saving due to the advantages of compact structure,high feasibility,strong safety,and stability,etc.To meet the needs of engineering applications,composite phase change thermal storage material,which is the key to this technology,has been extensively studied,and is developing in the direction of high thermal storage capacity and high thermal conductivity.Diatomite is a natural mineral with a porous structure and has been used as a support matrix in composite phase change thermal storage material.However,some structural characteristics need to be further explored and utilized,and emerging diatomite-based composite phase change materials(PCMs)are constructed to realize the regulation and enhancement of thermal storage performance.This paper strengthened the heat storage characteristics of diatomite from the aspects of pore structure and surface structure,and then loaded the phase change materials to construct the diatomite-based composite PCMs,and realize the application of light-heat conversion and storage.(1)It proposed a new method for improving the pore structure of diatomite to enhance thermal storage.Microwave-HCl modified diatomite(D)was used to load PCM(LA-SA)to prepare diatomite-based composite PCMs.After microwave-acid modification,diatomite has a larger specific surface area and pore space,which provides favorable conditions for the adsorption of PCMs.The maximum loading capacity of D and Dm to LA-SA is 41.3%and 51.7%,respectively.The diatomite(Dm)after microwave acid treatment has a higher load capacity.To further enhance the thermal storage and thermal conductivity of the composite PCM,a certain proportion of expanded graphite(EG)is added to diatomite to obtain a composite PCM(LA-SA/Dm/EG)with a maximum loading of 72.2%,and its latent thermal of melting and freezing are 117.30 J g-1 and 114.50 J g-1,respectively,the thermal conductivity value is increased by 214%.After 50 thermal cycles,it still has good thermal stability.(2)It revealed the mechanism of the surface of diatomite modified by manganese dioxide(MnO2)to enhance photo-thermal conversion.Three kinds of manganese dioxide modified diatomite support materials DP-MnO2 were synthesized by adjusting the concentration of the reactant potassium permanganate(KMnO4)through the hydrothermal reaction method.After loading the phase change material(LA-SA),the finalized composite PCMs were prepared.Due to the different concentrations of the reactant KMnO4,the pore structure of the obtained DPMnO2 is different,resulting in the difference in the load capacity and crystallinity of the support material.Among them,the composite phase change material LA-SA/DP-M2 prepared with DPM2 as the supporting material has a loading capacity of 42.2%,a melting temperature of 26.81℃,and a melting latent thermal of 66.74 J g-1.MnO2-modified the surface of diatomite not only enhanced the thermal conductivity of the diatomite-based composite PCM,but also made it have excellent solar energy collection efficiency,and strengthened the material’s lightto-thermal conversion performance.(3)It clarified the synergistic effect of the surface of diatomite modified by carbon to enhance thermal storage performance.Using calcium carbonate(CaCO3)as a template,sucrose as a carbon source,the support matrix(Dc)on the surface of diatomite modified by carbon particles is obtained by high-temperature calcination.The corresponding diatomite-based composite PCMs were prepared by the vacuum impregnation method.Exploring the influence of different calcination temperatures on the degree of carbonization of the diatomite surface,it is found that as the carbonization temperature increases,the size of the carbon particles generated on the surface of the diatomite increases.The diatomite modified by carbon nanoparticles has a larger specific surface area and pore space,leading to load more PCMs.The load and latent thermal in melting of LA-SA/D were 41.57%and 56.89 J g-1,respectively.While the load and latent thermal in melting of LA-SA/Dc-1000 was 49.92%and 70.07 J g-1,respectively.Futher research confirmed that carbon particle modification enhanced the thermal conductivity,photothermal conversion and storage capacity of the diatomite-based composite PCMs.This paper made full use of the mineral characteristics of diatomite and strengthened the thermal storage characteristics of diatomite,and constructed a series of diatomite-based composite phase change thermal storage materials by using interdisciplinary knowledge of energy science,materials science,and mineral processing.The relationships between pore structure,surface structure,and thermal storage performance of diatomite were established to realize the regulation of thermal storage performance,which provided a new idea for the preparation and application of high-performance thermal storage mineral materials.