Numerical Simulation And Structural Optimization Of Latent Heat Storage System With Fins

Latent heat storage technology is widely used in industrial waste heat recovery,solar heat utilization,building materials,electronic device cooling and other fields by virtue of its high energy storage density and the characteristics of approximately constant temperature energy storage.However,the low thermal conductivity of phase change materials restricts the development of the technology.As a simple and effective method of heat transfer enhancement,fin is also used in latent heat storage system.However,there are few studies on ring fins in latent heat storage systems.On the other hand,most studies only study heat transfer enhancement during melting process,and often ignore heat transfer process during solidification process.Therefore,in this paper,the thermal performance of the latent heat storage system with annular fins is studied and the structure is optimized.The main research contents are as followsThe melting and solidification processes of phase change materials(PCM)in heat storage units with the same volume and the same three-dimensional spaces occupied of annular fins and longitudinal fins were investigated numerically.Combined with the two finned structures,the influences of natural convection,placement mode and inlet direction of fluid on the melting process were studied,and the solidification process was compared.It is found that the melting and solidification time of annular finned structure is always shorter than that of longitudinal finned structure under the same model because the surface area of the annular fin is larger when the same volume and three-dimensional space occupied are the same.The results show that for the melting process,the annular finned structure placed vertically shows better thermal performance.However,for the solidification process,the annular finned structure placed horizontally shows better thermal performance.The existence of convection speeds up the melting and solidification process.In addition,it is found that the melting time in the heat convection model is reduced by 38.71%compared with that in the heat conduction model.In the solidification process,the value is 7.56%.The conclusion can be used to select the placement mode and fin in latent heat storage systemPrevious studies have shown that the bottom and top are heat transfer dead zones in the process of melting and solidification.Therefore,the unequal length annular fin arrangement is proposed.Under the condition that the fins volume is the same,the fin length at the bottom and top is increased,and decreased in the middle.In order to evaluate the thermal performance of the heat storage system,taking the uniform finned structure as base case,combined with heat/release storage increment and heat/release time reduction,the concept of growth rate is proposed.The results show that the proposed initial optimized structures can improve the melting process,to further improve the thermal performance,the method of partition is proposed for quadratic optimization.It is found that the quadratic optimized structures show superior thermal performance in both melting and solidification processes.When the partition number is four,the growth rates in melting and solidification process are 29.91%and 13.15%respectively.In order to generalize the results,two dimensionless correlations formula for Fo and average Nu in the melting process are proposed which can be applied in a practical design of the latent heat storage systemsOn the other hand,considering that the design of unequal length may increase the cost of fin manufacturing,another optimization method,unequal fin space is proposed in which the fin spacing varies in proportion.And the quadratic optimization is proposed by moving fins in both ends towards to ends.The results show that the two optimization methods significantly improve the heat transfer in the melting process,and the maximum growth rate is 14.94%and 26.79%in the two optimization methods.Yet the two methods have weak promotion effect on the solidification process,the maximum growth rate is 4.79%.Therefore,three-time optimization is proposed for improving solidification process by arranging fins evenly in the middle and densely in the ends.Results show the growth rate can be up to 15.78%.Moreover,the growth rate in melting process further reaches to 30.46%.Finally,two dimensionless correlations for Fo and average Nu for initial and quadratic optimized structures are proposed which can be used in fin positioning design.