Volume-constrained multiphysics topology optimization of fin structures for cryogenic adsorption hydrogen storage tank

To enhance the heat transfer efficiency and adsorption performance of the cryogenic adsorption hydrogen (CAH2) storage tank filled with activated carbon (AC), this study conducted a topology optimization(TO) model of the internal fin structure. Based on the Darcy flow-heat transfer-adsorption multi-physics governing equations of the adsorption hydrogen process, a density-based topology optimization mathematical model and computational framework is established, with enhanced heat transfer as the optimization objective under volume constraints. The Modified Dubinin-Astakhov (MDA) isotherm adsorption equation is used to characterize the adsorption-exothermic process of AC, and the volume constraint factor f _v is applied to quantify the trade-off between fin topology volume and effective adsorption volume. Optimization results reveal the iterative coupling among the evolving fin-material distribution, objective-function optimization, and coupled flow-heat-adsorption fields. The fin structure exhibits significant regularity as f _v increases, indicating a trade-off between heat transfer efficiency and effective storage volume. While larger f _v enhances heat transfer, it reduces the available adsorption volume, wherein the fin structure at f _v = 0.075 achieves the optimal balance. The overall fin topology features a V-shaped channel along the hydrogen flow direction, enabling a synergistic effect of global multi-branch heat conduction and central-axis flow guidance. This strengthens the removal of adsorption heat and compression work, accelerates hydrogen flow and heat transport at the tank bottom, and improves the adsorption rate and uniformity. Compared with traditional rectangular-fin and no-fin designs, the TO-fin achieves synergistic improvements in heat transfer efficiency, temperature uniformity, and adsorption performance by increasing the heat exchange surface and enhancing uniform hydrogen diffusion. Consequently, the stored hydrogen mass increases by 5.8% and 10.7%, and the time required to reach the same adsorption mass is saved by 29.8% and 47.5%, respectively. This study provides a new theoretical basis and methodological path for efficient CAH2 tank design.