Numerical study on melting process and heat transfer analysis of a multitube combination latent heat storage unit with innovative harpoon-type fins

The heat transfer rate of a coupled system combining a passive residual heat removal system and a latent heat thermal energy storage system is directly related to worker safety in nuclear power plants. To enhance the heat transfer performance of the coupled system, in this study, the melting process of phase change material in the latent heat thermal energy storage system is numerically investigated by inserting innovative harpoon-type fins. A new assessment index is also proposed to evaluate the comprehensive heat transfer performance of fins. More than thirty cases with different harpoon-type fins are designed, and the impacts of various efficient structural parameters of the harpoon-type fin on the melting process are evaluate. The response surface method is used to optimize the structure. The results demonstrated that the handle length and the number of fins significantly improve the heat transfer performance of the harpoon-type fin. The optimal geometrical parameters (arc angle & theta; = 45 degrees, handle length Lha =10 mm, fin number Nf = 8, and arc number Na =1) of harpoon-type fins are obtained. The heat transfer rate of the optimal fin structure is six times that without fins, and the total melting time is shortened by 85.9%. Furthermore, the longitudinal extension of the fins is more important than the complex horizontal extension of fins. The harpoon-type fin not only shows better performance in the coupled system but can also be used in shell-and-tube latent heat thermal energy storage systems.