[Objective] To achieve recovery and utilization of low-grade waste heat

we proposed a phase change thermal storage unit incorporating “tree-branch fins + foam metal”

and co-optimized its structural and material parameters using response surface methodology and orthogonal experiments. [Methods] Under typical operating conditions(80 ℃

0.005 m/s)

tree-branch fins reduced the melting time of the phase change material(PCM) by 10.7% compared to straight fins

with optimal parameters including a length ratio of 1.143

a width ratio of 1.057

and a branching angle of 68.987°. Regarding system structure

the counterflow arrangement of dual heat exchanger tubes decreased the melting time to 558 s

and further filling with foam metal shortened it to 181 s. Although increasing porosity enhances the proportion of PCM

it weakens the structural support of the metal framework

thereby prolonging the melting time. [Results] In conclusion

the integration of tree-branch fins and foam metal significantly improves the thermal storage performance of phase change thermal storage devices. Subsequently

staged thermal energy storage can improve the efficiency of heat storage. The optimal configuration for a threestage cascade is put forward: Stage Ⅰ: 0.9 porosity nickel foam + n-octadecane; Stage Ⅱ: 0.5 porosity nickel foam + n-octadecane; Stage Ⅲ: 0.5 porosity nickel foam + stearic acid PCM. [Conclusion] It can provide an integrated design basis for the efficient capture and reuse of low-grade waste heat at 50～60 ℃.