Simulation of Micromachined Chemical Reactors for Heterogeneous Oxidation Reactions

We present Galerkin "nite element simulations of two- and three-dimensional #uid #ow, thermal "elds, and chemical species concentrations in micromachined chemical reactors. Such microchemical systems have potential for increased safety and on-demand manufacturing compared with conventional macroscopic reactors. The simulation approach incorporates a general mesh generation procedure that enables di!erent microchemical reactor designs to be explored. The nonlinear di!erential-algebraic equations resulting from the "nite element discretization are solved by Newton’s method augmented with a pseudo-arc-length continuation scheme for tracing ignition and extinction points. The predicted temperature pro"les are in good agreement with experimental data from temperature sensors located along the heater unit of the microreactor. The results also mirror observed ignition}extinction behavior by demonstrating that at low #ow rates ignition occurs downstream and the reaction front subsequently travels upstream due both to heat conduction and the presence of fresh reactants upstream. Upstream movement of reaction front diminishes at high #ow rates because signi"cant reactions occurring downstream cause the downstream temperature to climb. The good agreement between simulated and observed results encourage further use of reaction engineering analysis and design tools in evaluation, scale-up, and application of microchemical systems. ( 1999 Elsevier Science Ltd. All rights reserved.