Improved hydrogen production performance of methanol steam reformer by integrated with tree-like network and Sierpinski carpet

Methanol steam reforming (MSR) is a promising approach for mobile hydrogen production. However, the hydrogen production performance is greatly affected by the reaction kinetics and the processes of heat and mass transfer. Additionally, scaling down the reaction system to achieve efficient and continuous hydrogen production is a considerable challenge. To improve the fluid flow, heat transfer, and chemical reaction performance of the reforming system, a novel fractal microreactor with integrated tree-like microchannel and Sierpinski carpet structure is designed in this study. A topology optimization method based on diffusion resistance minimization and different constraints is proposed. The fluid flow, heat transfer, and chemical reaction in the fractal microreactor are simulated by the finite element method. The results indicate that the optimal successive length ratio of the tree-like microchannel obtained by constraining the channel area and minimizing diffusion resistance is 0.707, and the optimal successive diameter ratio is 0.500. Fractal microreactors equipped with the optimally structured tree-like microchannel have better heat and mass transfer performance. Compared with the 0th order reactor, the Nusselt number increases with an average step size of 3.75 % as the order of fractal iteration increases. The methanol conversion and CO relative concentration increase with the increase of steam/CH3OH mole ratio and reforming temperature, and the methanol conversion decreases with the increase of mixed steam feed flow rate. In addition, the 4th order fractal microreactor with the best continuous ratio can effectively improve the hydrogen utilization efficiency by about 1.6–1.7 %. This study provides a reasonable reference for the performance improvement of hydrogen production and the structural design of microreactors.