Preparation And Properties Of Paraffin-Expanded Graphite And Lauric Acid-Expanded Graphite Composite Phase Change Materials

Phase change energy storage technology is a technology that uses materials to store heat by absorbing or releasing energy to change the material state when the ambient temperature changes.it can provide higher storage capacity per unit mass.it has the characteristics of storing heat as latent heat of melting at a constant temperature,and is widely used in many fields of life and industrial production.For the cold areas with relatively cold outdoors and large indoor heat demand in winter,building heating is often connected with clean heat sources such as solar energy,but when the energy demand and supply do not match,the application of phase change heat storage technology to the heating field of low-temperature buildings can effectively save fuel and avoid wasting resources and reduce the operating cost of the whole building system.Based on this,the purpose of this paper is to select the energy storage materials which are suitable for coupling with the local solar energy-building heating system by analyzing the heat transfer mechanism of phase change energy storage and combining with the local climatic conditions.Firstly,through the selection principle of phase change materials,paraffin and lauric acid with phase transition temperature of43±0.5℃were selected as phase change materials,while expanded graphite with high thermal conductivity and honeycomb porosity was selected as supporting materials.Paraffin-expanded graphite and lauric acid-expanded graphite composite phase change materials were prepared by melting mixing method,and the phase and apparent morphology of the composite phase change materials were characterized by FT-IR and SEM.The thermal performance of the material is tested by laser thermal conductivity meter and DSC,and the law between the content of expanded graphite and the performance of the material sample is studied by adjusting the mass ratio of expanded graphite in the material sample.Combined with the comprehensive comparison of the economic properties of the material,some suggestions for the selection of heat storage materials under the low temperature environment of building heating are put forward.The experimental results show that the expanded graphite prepared by microwave expansion method shows obvious worm shape and rich and loose porous honeycomb structure,which can be used for phase change materials,and it is found that there is no new material in the composites,which is only a simple physical chimerism of the original materials,and the chemical compatibility is good.After SEM detection,it is found that the exposed phase change material/loose grid structure still exists when the content of expanded graphite is low/excessive,while when the expanded graphite is uniformly adsorbed,the composite still keeps worm-like structure and has good physical compatibility.Through thermal conductivity test and DSC test,it is found that the addition of expanded graphite has little effect on the phase transition temperature of the material,but the increase of thermal conductivity is more obvious,and the latent heat of phase transformation decreases accordingly.When the proportion of expanded graphite is from 4%to 20%,The heat transfer coefficient of paraffin-expanded graphite/lauric acid-expanded graphite increased from 0.238 and 0.345 W·（m·k）^-11 to 1.789 and1.548 W·（m·k）^-11 respectively,and the latent heat of phase transformation decreased from 136.912 and 149.729 J·g^-11 to 102.940 and 113.836 J·g^-1,respectively.Under the premise of ensuring the composite material and heat storage capacity,the addition of expanded graphite should not exceed 18%.Combined with thermal performance and economy,the thermal performance of lauric acid-expanded graphite is better than that of paraffin-expanded graphite at the same content of expanded graphite,and the latent heat storage cost of paraffin-expanded graphite composite phase change material is lower under the same heat storage capacity.Under the premise of the same heat storage cost,the heat storage capacity of lauric acid-expanded graphite is better.