Research On Fatty Acids And Methyl Esters Composite Phase Change Thermal Storage Materials

In this paper,a series of fatty acid-fatty acid and fatty acid-methyl ester binary composite systems with a fatty acid core were prepared with the aim of developing phase change materials（PCM）suitable for low-temperature energy storage applications such as building energy efficiency and thermoregulated textiles.Among them,capric acid-palmitic acid and methyl palmitate-lauric acid have suitable phase transition temperature and high energy storage density,which are ideal materials for low-temperature energy storage applications.In order to overcome the low thermal conductivity common to fatty acids and the defect of liquid leakage when exceeding the melting temperature,this paper selects expanded graphite（EG）as the shape stabilizer and thermal conductivity enhancer to prepare CA-PA/EG composite shape-stabilized PCM to improve the overall performance of CA-PA binary composite system;on the other hand,considering a large number of studies on carbon-based porous carriers,it is difficult to give more advanced functions to PCMs so far.Therefore,the functionalized design of PCM support carriers becomes one of the topics of this paper.The new MP-LA/MgO/EG composite PCMs were prepared by mixing MgO nanoparticles with the MP-LA binary composite system as a new nano-filler.Further modern analytical testing techniques such as SEM,FT-IR,XRD,DSC,and TG were used to characterize the microscopic morphology,chemical structure,thermal properties,thermal stability and reliability of the CA-PA/EG and MP-LA/MgO/EG composite shape-stabilized PCMs,and to explore in-depth the mechanism of the effect of composition and structure on thermal conductivity enhancement and shape stability.The CA-PA/EG composite shape-stabilized PCM obtained by adding 9 wt.%of EG to the CA-PA eutectic mixture has a phase change temperature of about 299.5 K and a latent heat of 137.6 J·g^-1.FT-IR results show that CA-PA and EG are physically bonded together and are compatible.The addition of the thermal conductivity enhancer EG increased the thermal conductivity of the composite PCM by a factor of 16.09 to approximately 3.914 W·m^-1·K^-1.Meanwhile,100 accelerated thermal cycling tests and leakage analysis showed that the addition of 9 wt.%EG improved the thermal stability and reliability of the CA-PA binary eutectic mixture.A novel support material MgO/EG,synthesized by the template-method,maintains the porous structure of EG for encapsulation and deformation while reducing the interface thermal resistance between the matrix and the PCM molecules by means of MgO to maximize heat conduction.The results show that the thermal conductivity of the novel MP-LA/MgO/EG composite PCM(4.568 W·m^-1·K^-1)is 8.16 times higher than that of pure MP-LA.And the DSC analysis shows that the enthalpy of the composite PCM floats in a narrow range with the value of 1.88%during the process of heating-cooling cycles 100 times.The infrared images visualize the ability of the composite PCM to respond more sensitively to temperature changes.The composite PCM achieves a simultaneous improvement in thermal stability and thermal conductivity.In addition,the composite PCM has a latent heat value of 166.9 J/g（phase transition temperature of 304.1 K）and has excellent thermal storage capacity.