| At present,solid-liquid phase change materials are widely used in construction,solar energy,air conditioning system,textile,heat dissipation and other fields because of their advantages such as large latent heat and controllable phase change temperature.However,solid-liquid phase change materials have the problems of easy leakage and low thermal conductivity during the phase transition,which limit their practical applications in heat storage.In this paper,paraffin was selected as the phase change material,and its leakage rate was reduced by microencapsulating the paraffin and then encapsulating it with the polymer matrix.The thermal conductivity was improved by adding high thermal conductivity graphene nanoplatelets(GNPs).Finally,the heat transfer of composite PCMs in thermal applications was simulated based on numerical simulation methods to predict the application prospects of the material.The main contents of this paper as follows:(1)SR/Pn@SiO2/GNPs shape-stablized phase change materials were prepared by solution blending and melt blending methods.The effects of Pn@SiO2 and GNPs on each property of the materials were investigated,respectively.As shown by the cross-sectional SEM images,Pn@SiO2 and GNPs were completely wrapped by the SR matrix,uniformly distributed in the SR matrix,and the two-dimensional lamellar GNPs did not curl.This is a prerequisite for the good thermal conductivity and mechanical properties of the SR/Pn@SiO2/GNPs phase change composites.In the investigation of the effect of GNPs content on composite properties(SPG),the thermal conductivity of SPG was proportional to the GNPs content and coincided with the theoretical model of the effective thermal conductivity of GNPs-based composites.In the investigation of Pn@SiO2 content(SGP),the enthalpy of SGP could be adjusted according to the Pn@SiO2 content,and the enthalpy of the prepared SGP phase change composites ranged from 25.6 to 78.49 J·g-1.Due to the adjustable enthalpy,the SGP composites exhibited different temperature regulation in the thermal energy storage/release analysis.Both showed excellent leakage resistance in the leakage rate test,with the highest leakage rate not exceeding 0.6%.The hardness of the SR/Pn@SiO2/GNPs phase change composites decreased with increasing temperature and was stable at about 20 at 80°C.(2)The application of SR/Pn@SiO2/GNPs phase change composites in the field of heat dissipation was investigated using CFD software.The effects of the variation of GNPs and Pn@SiO2 content on the heat dissipation were discussed.The temperature and solid-liquid interface clouds visually reflect the heat transfer mode,phase change state,temperature control effect on the coppert and the heat transfer rate of the SR/Pn@SiO2/GNPs phase change composites.The simulation results showed that the heat transfer mode of the phase change composites during melting was still dominated by heat conduction.Increasing the content of GNPs increased the thermal conductivity of the composites,improved the heat transfer rate of the samples,and transfered the heat quickly from the copper to the heat sink for heat dissipation,so the temperature difference between the copper and the environment was small.And increasing the Pn@SiO2 content extended the time for copper to reach high temperature,which played a key role in copper temperature regulation.In general,both GNPs and Pn@SiO2improved the thermal performance of SR/Pn@SiO2/GNPs composites,GNPs by enhancing the thermal conductivity of the complosites to increased the heat transfer rate,and Pn@SiO2by using energy storage to absorb heat to prolong the time for copper to reach high temperatures. |
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