Modeling and evaluation of an integrated microfluidic fuel processor for miniature power sources

New lighter-weight, longer-lasting portable power sources are in demand to meet the special requirements for laptop computer, cellular phone, military and homeland security use. A microreactor technology based fuel cell can achieve high power and energy density by directly transforming chemical energy into electrical energy, thus providing an alternative to current secondary batteries. Proton exchange membrane fuel cell (PEMFC) is an attractive technology for low power level applications. In PEMFC applications, an on-board fuel processor would be desirable due to the difficulty associated with the storage and refilling of hydrogen. However, there are a number of technical challenges that need to be addressed for the development of portable fuel processor to become commercially viable. Miniaturization in terms of size and weight, fuel processor lifetime, and material and energy management are some of the most critical issues. In this presentation, we describe the design and simulation of a micro-reactor-based fuel processor on silicon wafers for a 20 W PEMFC with steam reforming of methanol. A hardware integration scheme, which incorporates four major components: vaporizer, reformer, preferential oxidation reactor (PrOx) and combustor, several internal heat exchangers, and some internal thermal barriers was proposed. A complete two-dimensional CFD simulation of the integrated system involving flow, heat and mass transfer as well as chemical reactions was performed. Detailed information such as species concentration profiles, reaction extent, temperature profile and energy usage was obtained. The size of each major equipment component including the internal heat exchangers was determined, as well as the thickness of the insulators separating them.