Numerical Simulation And Optimization Of Binary Composite Phase Change Material Heat Accumulator

Global warming is a major challenge in the current humanity,and increasing the use of renewable energy is a clear way to achieve climate change.Solar resources are rich,but there are intermittent shortcomings.Phase change accumulator combined with a solar thermal utilization system can solve the intermittent problem of solar energy.The heat storage and release performance of phase change heat accumulator directly affect the whole solar heat utilization system,phase change materials and the structure of phase change accumulator are the core factors affecting the heat storage and release performance of phase change accumulator Therefore,it is necessary to study the screening preparation of phase change materials excellent in thermal properties and optimization of phase change heat accumulator structures.In this thesis,stearic acid-acetamide/expanded graphite binary composite change materials are prepared by the melt mixing method.Its phase change characteristics,phase and micro morphology,leakage,thermal conductivity and thermal stability were analyzed.The results showed that when the acetamide mixed mass ratio was 20%,the phase change temperature of the stearic acid-acetamide binary mixed-phase change material was 50.29℃,and the phase change latent heat was 196.71 J/g.When the mass ratio of expanded graphite is 16%,the stearic acid-acetamide/expanded graphite binary composite phase change material has good thermal conductivity,thermophysical properties and no leakage.The thermal conductivity reaches 1.523W·（m·k）^-1,the latent heat of melting and solidification is 163.24 J/g and 160.35 J/g,the melting and solidification temperature are 50.39℃and 47.53℃,respectively.The stearic acid-acetamide/expanded graphite binary composite change materials are used as the heat storage material of the phase change heat accumulator.The heat storage and release intensity are introduced as the evaluation index of heat storage and release performance of the phase change heat accumulator.In order to determine the factors affecting the heat storage and release performance of the phase change accumulator,the heat storage and release process of the phase change accumulator was numerically simulated.The results show that a commercial phase change heat accumulator under the same operating conditions is referenced,the heat storage and release intensity of the phase change heat storage material is increased by 40.2%and 17.06%,respectively.Changing the operating parameters such as the inlet temperature and flow rate of the heat transfer fluid of the phase change accumulator,changing the diameter of the heat exchange tube of the phase change accumulator and adding fins can improve the heat storage and release performance of the phase change accumulator.In order to further improve the storage thermal performance of the phase change heat accumulator.Based on the above studies,In this thesis,the operating parameters of binary composite phase change material accumulator are optimized by changing the inlet temperature and flow rate of heat transfer fluid.On the basis of the optimal operating conditions,the structural parameters of the phase change accumulator are optimized.The results showed that the optimum heat storage and release conditions of the phase change accumulator in this thesis are that the inlet temperature of heat transfer fluid is 353.15 K and 293.15 K,and the flow rate is0.55 m/s.Selection of stainless steel phase change heat accumulator material.The diameter of heat exchange pipes is 23 mm.Finally,the number of small sets of fins is 48,and the total area of fins is 3.882 m².The heat storage and release intensity of binary composite phase change material accumulator after final optimization is 67.7%and 46.7%higher than that of a commercial phase change accumulator,respectively.It provides reliable data for the optimization of phase change heat accumulators and a more effective way for better utilization of renewable energy.