Volume 47

Effects of fractal microreactor on mass transfer and reaction in methanol steam reforming Lianlian Xu, Haisheng Cui, Zhang Bai, Yunyi Han, Xiankun Huang, Yongxiao Tuo, Shuoshuo Wang

Abstract

Hydrogen production by methanol steam reforming (MSR) is one of the promising solutions for mobile hydrogen sources, particularly in applications like proton exchange membrane fuel cells (PEMFCs) and hydrogen refueling stations. However, due to the endothermic characteristics of MSR, its hydrogen production efficiency is greatly affected by thermal management, such as temperature gradient and cold/hot spot. Considering portability and integrated applications, miniaturizing the reaction system to achieve efficient continuous hydrogen production is also a significant challenge. Using fractal geometry in engineering applications can produce larger surface area and lower mass devices. In order to improve the heat and mass transfer as well as the chemical reaction performance of the reforming system, this study uses the Sierpinski carpet model, which integrates four iterations of fractal geometry, into the design of the MSR microreactor. The fluid flow, heat transfer, and chemical reaction processes in MSR fractal microreactor are simulated by the finite element method. A comparison is made with a flat plate type reactor (0th order). The results indicate that the heat and mass transfer performance of the fractal microreactors is higher than that of the flat plate type reactor. Compared with the 0th order reactor, the 4th order fractal microreactor can effectively improve the utilization efficiency of H by about 8.33% and improve the H2 production rate by 7.91%. In addition, a higher steam/CH3OH (S/C) mole ratio results in a higher H utilization efficiency, the relative concentration of CO at the outlet, and the H2 production rate, while a higher reforming temperature results in a lower H2 production rate. This study can provide a theoretical basis and technical support for the industrial application of microreactors in mobile hydrogen production and fuel cells.

Keywords methanol steam reforming, hydrogen production, microreactor, fractal