Research On Heat Transfer Characteristics Of Phase Change Accumulators Based On Cylindrical Heat Source And Fractal Framework

Phase change accumulator can well solve the problem of the mismatch between supply and demand in the process of energy utilization.It is widely used in energy storage because of its advantages such as small size of device,large amount of heat storage and approximate constant temperature in the process of heat storage.However,the thermal conductivity of the phase-change material is usually low,which affects the heat storage efficiency of the system.Therefore,it is necessary to optimize the phase change accumulator to improve its heat storage performance.In this paper,the internal structure optimization of the tube-shell phase change heat accumulator with inter tube and outer cavity is studied by numerical simulation.Firstly,lattice Boltzmann method suitable for solid-liquid phase transformation is introduced,and its effectiveness and accuracy are verified by three benchmark calculation examples.Secondly,for three-dimensional cases,the influence of the placement direction and position of the cylindrical heat source on the melting process of the phase-change material was investigated.Then,the influence of Rayleigh number,Prandtl number and Stefan number on the melting process is considered in the two-dimensional calculation region,and the related laws are summarized.Finally,the fractal tree-shaped fins were introduced into the heat accumulator.The fractal series,total number of branches,fractal dimension of length,fractal dimension of width,thermal conductivity and distribution patterns of the fractal dendritic fins were changed respectively without changing the total volume of the phase change material,and the enhancement effects on phase change heat transfer under different conditions were analyzed.Compared to the condition without fins,the numerical results indicate that the additional fractal tree-shaped fins in the tube-shell phase change heat accumulator greatly improves the melting efficiency.Moreover,the thermal conductivity,geometric parameters and distribution patterns of the fractal tree-shaped fins have important effects on the melting of the phase change materials in the accumulator.