Research On The Heat Transfer Performance Of Phase Change Heat Unit Based On Fractal Theory

With the increasingly serious energy consumption and energy shortage,latent heat storage technology based on phase change materials(PCM)has been widely used in solar energy utilization,power system "peak shaving and valley filling",HVAC,waste heat recovery and other fields due to its advantages of high heat storage density,large phase change temperature range,various phase change materials and high economy.Among many kinds of latent heat storage methods,solid-liquid phase change has attracted the most attention in practical application,but considering the low thermal conductivity of phase change material itself,it is of great significance to carry out the research on heat transfer enhancement of solid-liquid phase change and design a new type of efficient phase change heat exchanger unit for the rational and efficient utilization of energy.At present,the methods to strengthen the solid-liquid phase transformation heat transfer technology are mainly from the two aspects of the selection of phase change materials to achieve heat transfer and the structural design of heat exchanger unit.The former depends on the development and innovation of chemical materials,while the latter considers the characteristics of easy operation and low cost,and chooses to add fins to improve the heat transfer performance of phase change heat exchanger unit.In view of the excellent geometric structure of phase change heat storage device at present in this paper,fractal geometry and tree structure are extended to fin design,fractal fin structure is constructed,and a new solidliquid phase change heat exchanger unit is proposed,which can improve the heat transfer performance of latent heat storage process and improve the efficiency of phase change heat exchanger It can improve and provide new methods.Firstly,based on the theory of fractal geometry,this paper explores the relationship between the fractal fin structure parameters and the total thermal resistance of the fins,which provides the data support for the optimal design of phase change heat exchanger unit.Combined with the size of the target unit,the fin structure parameters with smaller total thermal resistance are selected to complete the design of the fractal fin phase change heat exchanger unit.Then,the numerical simulation software FLUENT is used to simulate the heat exchanger unit under the theoretical calculation design,to explore the heat transfer performance of the phase change material inside the unit under the influence of fractal fins,and to study the influence of different temperature parameters on the phase change process of the phase change material.It is found that the larger the phase change temperature difference is,the shorter the phase change process of the phase change material is,and the phase change temperature difference is the transformation time of ?T=15 K is three times longer than that of ?T=5 K.A visual experimental platform for the study of solid-liquid phase change heat transfer characteristics in fractal fin heat exchanger was designed and built.The morphology evolution of the two-phse interface during the melting process of PCM in fractal fin heat exchanger was observed in real time.The axial dynamic temperature characteristics and the temperature uniformity in the unit were measured and analyzed.