Preparation Of Ternary Composite Phase Change Blocks With High Thermal Conductivity And Optimization Of Its Thermal Conductivity

Phase change materials are the working medium of latent thermal storage technology,and their phase change characteristics and thermal properties have an important impact on the performance of thermal storage system.Compared with inorganic phase change materials such as hydrated inorganic salts and molten salts,organic phase change materials do not have inherent defects such as supercooling,phase separation and corrosion,and have good practicality.However,the thermal conductivity of organic phase change materials is low.The combination of organic phase change materials and porous carriers to prepare form-stable composite phase change materials can not only improve the thermal conductivity of composite phase change materials by means of the high thermal conductivity of the carrier,but also overcome the problem of liquid phase leakage when phase change materials undergo solid-liquid phase change.In many porous substrates,expanded graphite(EG)has the advantages of large pore volume and good compatibility with organic phase change materials,making EG-based composite phase change materials a type of form-stable composite phase change materials with large latent thermal and improved thermal conductivity,which has great application prospects.In view of the fact that the thermal conductivity directly affects the heat storage and release rate of phase change materials,and in order to adapt to the applications that require high heat storage and release rate,this paper is dedicated to improving the thermal conductivity of the EG-based composite phase change materials,and proposes the strategy of adding carbon materials to prepare ternary composite phase change blocks with high thermal conductivity,and further improve the thermal conductivity of ternary composite phase change blocks through optimization.In this study,in order to improve the thermal conductivity of organic/EG binary composite phase change blocks,firstly,an organic matter PA was selected as organic phase change material,and compounded with EG by melt compounding method to prepare PA/EG binary composite phase change materials.Then,adding carbon additives carbon fiber(CF)and graphite sheets(GS)with high thermal conductivity into the binary composite phase change materials,and the mixture was pressed into cylindrical block to obtain ternary composite phase change blocks with high thermal conductivity.The results show that the effect of adding GS is better than CF.The thermal conductivity of PA/GS/EG ternary composite phase change block is 16.5 W/(m?K),and the phase change enthalpy is 140.50MJ/m~3,which is close to that of the PA/EG binary composite phase change blocks.In addition,the PA/GS/EG ternary composite phase change block has an efficient heat storage and release rate,excellent photothermal conversion performance and good thermal reliability.To further optimize the thermal conductivity of PA/GS/EG ternary composite phase change blocks,the influence of the thickness and width-length ratio of GS on the thermal characteristics of the PA/GS/EG ternary composite phase change blocks was investigated.PA/GS/EG ternary composite phase change blocks was prepared by adding GS with different thickness and width-length ratio to the composite phase change blocks,and its thermal properties were tested.The results show that the optimal thickness of GS is 0.05 mm and the width-length ratio is 13/30.The radial thermal conductivity(perpendicular to the compression direction)of the PA/GS/EG ternary composite phase change block is 21.25 W/(m?K),which is59.8%higher than the PA/EG binary composite phase change block.And its axial thermal conductivity(parallel to the compression direction)is 46.37 W/(m?K),which is 138.8%higher than the binary composite phase change block.Meanwhile,the volume enthalpy of the ternary composite phase change block is 140.39 MJ/m~3,which is only about 0.08%lower than the binary composite phase change block.To sum up,the PA/GS/EG ternary composite phase change block possesses excellent thermal characteristics such as high thermal conductivity,large phase change enthalpy,efficient heat storage and release rate,excellent photothermal conversion performance and good thermal reliability.Therefore,PA/GS/EG ternary composite phase change block has great application prospects in waste heat recovery system,solar hot water system and other fields.