Preparation Of Carbon-based Phase Change Composites And The Study Of Their Properties

Nowadays,the world is facing a serious energy crisis,which makes it urgent to developing the corresponding energy storage technology and materials.Hence,Phase change materials（PCMs）,one of the energy storage materials,is attracting more and more attentions.Phase change materials is a kind of materials that can store or release energy by isothermal absorption through the process of phase change.It has the advantages of stable property,high energy storage density,constant temperature of phase change,etc.which can solve the contradiction between energy supply and demand.However,there are many drawbacks such as low thermal conductivity,leakage problem and few applications,which limited their large-scale application.In this paper,three-dimensional porous carbon aerogels composite s with organic solid-liquid phase modified materials is proposed,which not only alleviate the leakage problem,but also enhance the thermal physical and mechanical properties of the phase change materials.Which provides new research ideas and experimental data for the low-cost preparation of composite phase change materials,as well as its applications in the fields of thermal energy storage,photo-thermal conversion and thermal management.（1）Using cotton threads and polyvinyl alcohol as raw materials,polyvinyl alcohol was used as the coating shell to prepare cotton threads bar,then carbonized it to obtain carbonized aerogels.which porosity is up to 85.36%,and the median pore size is about 3.954μm,indicating that its structure and pore size are suitable for capillary effect that can absorb octadecylamine（ODA）well,which not only making its enthalpy reach 203.3 k J·kg^-1,but also shows excellent leakage resistance property.This method also takes advantage of the uniform orientation characteristic given by cotton thread during industrial processing to bring heat transfer enhancement effect,which show a obvious anisotropic thermal conductivity characteristics,and making its thermal conductivity up to 0.3918 W·m^-1·K^-1.Compared with pure octadecylamine,the thermal conductivity is improved by 321%,which has the potential to be applied in the field of heat storage.（2）Polymer colloidal was prepared by Guar gum（GG）and Expandable Graphite（EG）through simple blending method,and a kind of aerogels with better properties was prepared by freeze-drying process.The porosity of aerogels is up to 91.78%,and the average pore size is about 14μm,which is conducive to the adsorption of phase change materials.Therefore,the enthalpy value can reach about 213.5 and 122.9k J·kg^-1 after the adsorption of octadecylamine and paraffin.In the compression test,its compressive capacity can reach 0.21Mpa.And compared with pure octadecylamine and pure paraffin,its thermal conductivity has also been improved t o a great extent,reaching 0.7992 W·m^-1·K^-1 and 1.459 W·m^-1·K^-1,respectively.Compared with pure phase change materials,it has increased b y about 655%and 454%respectively.At the same time,this low-cost material also has a wide spectrum absorption range,with a maximum absorbance of 94%,enabling it to achieve a maximum photo-thermal conversion efficiency of 86%,thus demonstrating a new inexpensive way to achieve photo-thermal conversion.（3）Locust bean gum（LBG）was used as a colloid.By exploring its crosslinking characteristics to achieve higher crosslinking degree,make more Expandable Graphite could be combined to form a series of excellent pore structures,achieving up to 8.840m²·g^-1 pore area and a maximum thermal conductivity of 3.456 W·m^-1·K^-1.The mechanical properties and performance to adsorb phase change materials have been improved.When the deformation rate of the aerogels reached 80%,the compressive performance of the aerogels could reach 0.34 MPa,and the enthalpy value of the composite phase change material after adsorption of octadecylamine could reach229.7 k J·kg^-1.When conducting passive thermal management on the ho t side of a Thermoelectric cooler（TEC）unit,the cooling time of the cold side was increased by more than 330%compared with the bare substrate.Which prove it has a good effect on the thermal management of electronic equipment such as TEC system.