From Density Functional Theory to Microchemical Device Homogenization: Model Prediction of Hydrogen Production For Portable Fuel Cells

Microchemical devices exhibit a wide spectrum of length and time scales. In this paper, we discuss hierarchical multiscale simulation of structured microreactors with square posts. Semiempirical models are used in conjunction with density functional theory to develop quantitative microkinetic models. Sensitivity Analysis (SA) and a posteriori zero-order asymptonics are employed to derive a one-step reaction rate expression that enables efficient computational fluid dynamics (CFD) simulations. The effects of catalyst surface area and dimensionality on microreactor performance are discussed. It is shown that the post microreactor exhibits nearly perfect mixing in the transverse direction, but significant back mixing in the longitudinal direction, especially at low Peclet numbers. A 1D diffusion-convection-reaction (DCR) model. with an effective diffusivity computed using homogenization theory, is employed and found to adequately describe the CFD simulations. This 1D DCR reactor model with one-step reaction model could he an efficient means for reactor optimization while retaining features from diverse scales ranging from quantum mechanics to device structural characteristics.