Preparation And Thermal Conduction Mechanism Of CNTs BN/Myristic Acid Composite Phase Change Materials

In recent years,with the continuous consumption of energy,all kinds of resources are becoming more and more scarce.In the context of the adjustment and reform of the world energy field,China's consumption revolution and energy production are growing rapidly.Therefore,it is urgent to improve the efficiency of energy utilization,and heat storage technology is one of the main measures to improve the efficiency of energy utilization.Because of its excellent energy storage efficiency,small temperature change and compact structure,phase change thermal storage has a bright application prospect in the field of energy utilization.Among them,phase change material plays a key role in phase change heat storage technology,and it is also the key of phase change technology.Phase change materials have strong heat storage capacity and heat conduction performance.As a kind of functional application materials with considerable application prospects,composite phase change materials can be widely used in textile,construction,aerospace and many other industrial fields.In this paper,myristic acid was used as phase change material and carbon nanotubes(CNTs)and boron nitride(BN)with excellent thermal conductivity were used as thermal conductive fillers.Based on the synergistic effect between carbon nanotubes and boron nitride particles,carbon nanotubes boron nitride / myristic acid composite phase change heat storage materials were prepared by melt blending method under the condition of less filling,and the change of phase change heat storage performance of composite phase change materials was analyzed.Then,the influence of the ratio of the two kinds of nanoparticles,the diameter of carbon nanotubes,the mass fraction of the mixed nanoparticles and different ambient temperature on the equivalent thermal conductivity of the composite phase change materials is analyzed.Based on the previous research,the prediction model of the thermal conductivity of the composite phase change materials with binary mixed nano fillers is established,The mechanism of thermal conductivity enhancement of composite phase change materials is systematically described.According to the above research,the following conclusions are drawn:(1)compared with pure myristic acid,the specific heat capacity of composite phase change material decreases gradually,while the corresponding thermal diffusivity decreases gradually,the loss rate of phase change enthalpy is less than 7.9%,and the phase change temperature only decreases about 1 ?.After 300 times of cold and hot cycle experiments,the change of phase change enthalpy and phase change temperature of composite phase change material is not obvious.(2)The composite phase change materials were characterized by powder X-ray diffraction(XRD)and scanning electron microscopy(SEM).It was found that with the addition of carbon nanotubes and nano boron nitride,no new materials were formed.(3)The thermal conductivity of cnt-bn / myristic acid composite phase change material increases with the increase of the mass fraction of nano thermal conductive filler.At the same mass fraction,the smaller the diameter of carbon nanotubes,the better the thermal conductivity of the materials.When the ratio of carbon nanotubes and boron nitride is 1:1,the thermal conductivity of myristic acid is the best.The proposed Maxwell modified model can well predict the thermal conductivity of carbon nanotube nano BN / myristic acid composite phase change heat storage materials with low loading,and the error can be kept within 3%.Based on the study of heat conduction path and the calculation of interface thermal resistance,the heat conduction mechanism of nanotube boron nitride / myristic acid composite phase change heat storage materials is systematically expounded from the micro point of view,aiming at the heat propagation of phonon in phase change heat storage materials.