Study On Thermal Properties Of Carbon Nanoparticles Reinforced Graphene Foam Composite Phase Change Materials

With the aggravation of the energy crisis,as an intermediate link in the process of energy conversion and utilization,energy storage system is a key technology in solving the problem of time,space and intensity mismatch between energy supply and demand and improving the stability and reliability of the system.Phase change energy storage technology has become a research hotspot in the field of energy and materials because of its high stability and wide working temperature range.Phase change materials(PCMs)determine the performance and reliability of energy storage system and play a vital role in promoting the development of new energy and improving energy utilization.There are many kinds of phase change materials,and the traditional phase change materials seriously affect the heat absorption and release efficiency of the energy storage system and hinder the application of phase change energy storage materials in the energy storage system because of their disadvantages such as low thermal conductivity,low energy storage density and high undercooling.In this dissertation,carbon matrix composite phase change materials are taken as the research object.Graphene foam with very high specific surface area is selected as the matrix material,polyethylene glycol is selected as the phase change core material,and carbon nanomaterials with different dimensional pores are selected as the thermal performance enhancer,including two-dimensional planar graphene nanosheets,one-dimensional hollow carbon nanotubes and threedimensional porous carbon nanospheres,The effects of carbon nano reinforcements on the structural properties and loading capacity of composite phase change materials were systematically investigated;Aiming at the problem that the energy storage density and thermal conductivity of composite phase change materials are difficult to give consideration to and the application scope is single,a series of carbon based composite phase change materials were prepared.The effects of adding carbon nano reinforcers with different pore latitudes on the thermal storage and heat transfer characteristics and photothermal conversion capacity of composite phase change materials were investigated,and a composite phase change material with both thermal storage and heat transfer characteristics and enhanced photothermal conversion efficiency was prepared.Its thermal conductivity can reach 0.73W/(m·k).The phase transition enthalpy is 135.83J/g,and the photo thermal conversion efficiency is 89.76%;By improving the assembly method of carbon nanotubes and optimizing the preparation method of the assembly substrate,the thermal performance of composite phase change materials is further improved.It is proposed that hollow and porous carbon nano reinforcements can enrich the multi-level pore network structure of composite phase change materials,improve the load capacity of composite phase change materials,and more effectively improve the energy storage density and heat transport capacity of composite phase change materials;Using molecular dynamics method,taking carbon nanotubes as the representative of nano reinforcer,an amorphous carbon carbon nanotube assembly substrate model was constructed.The effects of different carbon nanotube filling and assembly methods on the heat storage characteristics of composite phase change materials were explored from a microscopic perspective,and a multi-stage porous enhanced energy storage density theory of "large hole lifting load,small hole lifting load" was proposed and verified;A theoretical model of assembly substrate is proposed to connect carbon nanotubes with graphene by chemical bonding,which makes the assembly substrate form a whole,strengthens the integrity of the three-dimensional through network structure,reduces the interface thermal resistance of composite phase change materials,and enhances the thermal transport capacity of the energy storage system.