Study On N-nonadecane/CaCO₃ Microencapsulated Phase Change Material And Its Thermal Properties

The phase change energy storage material（PCM）can absorb the heat generated during the charging and discharging process of the battery in the form of latent heat,it can regulate the working temperature of the battery,and prevent spontaneous combustion or even explosion of the battery due to thermal runaway.Due to the leakage problem in the specific application of PCM,the encapsulation of PCM can effectively avoid the leakage problem in the solid-liquid phase change process,and at the same time improve the thermal conductivity,mechanical strength,durability and other properties of PCM.In this paper,a new MicroEPCM and its latent functionally thermal fluid（LFTF）were prepared for the application of battery thermal management.The thermal properties of MicroEPCM and LFTF were studied.The main research contents and conclusions of this paper are as follows:（1）A novel n-nonadecane/CaCO₃ MicroEPCM was prepared by encapsulating n-nonadecane with high thermal conductivity material CaCO₃,and its structure and thermal properties were tested.FTIR and X-ray diffraction showed that n-nonadecane was successfully encapsulated by CaCO₃.The TEM confirmed that the product had a distinct core/shell structure.The process parameters such as reaction core/shell mass ratios,striing rate,temperature and emulsifier concentration were changed,and the effects on the micro-morphology and thermal properties of MicroEPCM were investigated.The optimum reaction conditions for the preparation of the MicroEPCM were obtained.Experiments showed that when the core/shell mass ratio was 3:1,the stirring rate was 800 rpm,the reaction temperature was set to 45°C,and the emulsifier concentration was 15 mmol/L,the prepared MicroEPCMs have a smooth spherical structure and uniform particle size.The latent heat of phase change was as high as 134.83 J/g,and the encapsulation rate was 59.68%.（2）The thermal conductivity of the n-nonadecane/CaCO₃ MicroEPCM was tested by a thermal conductivity tester.It was confirmed that the thermal conductivity of the MicroEPCM was significantly improved after the introduction of the high thermal conductivity inorganic wall material of CaCO₃,and the thermal conductivity at room temperature was improved.up to 3.58 times that of n-nonadecane.The MicroEPCM did not leak after being heated at 80°C for 20 h,which proved that the CaCO₃ shell was compact and had good packaging effect.By TGA,n-nonadecane began to degrade at 150°C,and the MicroEPCM showed mass loss at 170°C,indicating that the dense CaCO₃ shell can effectively prevent the decomposition of core material at high temperature.After 200 times DSC cycle test of MicroEPCM,the MicroEPCM still showed good phase change characteristics,which proved that they have good thermal stability and durability.The MicroEPCM also have high mechanical strength and maintain good structural properties and latent heat of phase change after continuous mechanical stirring.（3）Based on the n-nonadecane/CaCO₃ MicroEPCM,a latent heat functional fluid（LFTF）with mass fraction of 5wt.%,10wt.%,15wt.%was prepared,and its density,particle size,mechanical stability,phase change characteristics,thermal conductivity and viscosity were tested and characterized.The latent heat of LFTF with mass fractions of 5 wt.%,10 wt.%,and 15 wt.%were 6.43 J/g,13.04 J/g,and 19.24J/g,respectively,and the error with theoretical latent heat was less than 5.11%.At the same temperature,the fluid after adding the MicroEPCM have a thermal conductivity lower than that of the base liquid.At the phase change temperature of the n-nonadecane,the thermal conductivity of the LFTF was slightly reduced due to the solid-liquid phase transition.At other temperatures,the thermal conductivity of the same LFTF increased with increasing temperature.Comparing the measured viscosity values with the theoretical values calculated by empirical formulas such as Einstein,Brinkman-Roscoe,Batchelor and de Kruif,the results showed that for the 10wt.%LFTF,the empirical formula of viscosity is applicable.The error was less than 5.2%.For the 10wt.%LFTF,the de Kruif empirical formula has a higher applicability,and the maximum calculation error is not higher than 5.8%.When the mass fraction was15wt.%,the viscosity of the fluid increased sharply,and the above empirical formulas were no longer applicable.