The Study Of High Thermal Conductivity Composite Phase Change Materials For Low Temperature Energy Storage

Phase change materials have the merits of fixed melting point and high thermal energy storage density.Energy storage systems and thermal management systems designed with low temperature energy storage materials have important application prospects in daily life,electronic devices and aerospace vehicles.This thesis focuses on the study of materials with high energy density per unit volume?literature value>300 J/cm³?.We selected two low temperature alloys and Na₂HPO₄·12H₂O hydrated salts to study.The main research contents include the thermal properties of the materials,the thermal conductivity enhancement,the performance test of packaged modules,and the possible applications.In the study of low temperature alloys,we choose two Sn-In based alloys with melting points of 47°C and 60°C,respectively.Based on the T-history method,we experimentally measured the latent heat of the two low temperature phase change alloys,and found that their latent heats were only 252 J/cm³ and 206 J/cm³,which is much smaller than the literature value.We provided accurate latent heat value for these two alloys for the first time.The 47°C phase change alloy was further used to make a heat storage module.The thermal management capability of the module was tested with electric heaters.The results showed that under a heating power of 10W,with the temperature of the heat source below70°C,80mm×12mm×5mm heat storage module can extend the working time of electronic devices to about 110 seconds.In addition,tests have shown that alloy phase change materials have excellent thermal conductivity and can meet the thermal conductivity requirements in general applications.In the study of Na₂HPO₄·12H₂O hydrated salt phase change materials,because Na₂HPO₄·12H₂O has two relatively close phase change points,the experimental platform was built using the traditional method to determine the latent heat in different phase transitions of Na₂HPO₄·12H₂O.In order to enhance the thermal conductivity of Na₂HPO₄·12H₂O,the copper foam was filled with the material to form a composite heat storage module.The temperature of the center and edge of the heat spreading plate under different heating powers is tested,the results show that the temperature difference decrease as the thickness increases;under 6 W power heating,if the required temperature difference of the heat spreading plate does not exceed 4°C,The thickness shall not be less than 0.5mm.When the hot spot temperature of the heat spreading plate does not exceed 70°C,the30mm×30mm×7mm heat storage module can work for approximately 600 seconds.In addition,this thesis also studied the simulation method for Na₂HPO₄·12H₂O,the two phase change intervals material.Using the apparent heat capacity method,considering the two phase change intervals and one phase change interval respectively,the numerical simulation of the non-steady heat storage process of the Na₂HPO₄·12H₂O composite heat storage module was performed.The results show that,the method of using two phase change points has higher precision;at high power,the two methods show similar results.Finally,this thesis introduced two applications using low temperature phase change energy storage materials,including a quick-cooling thermostatic cup and a safe non-electric-heating thermostatic foot tub.Experimental tests showed that the quick-cooling thermostatic cup can quickly cool the boiled water and maintain a suitable drinking temperature for a period of time.