In many natural systems, the lack of mixing is a primary limiting factor in the rate of chemical reactions. The poor mixing can be imparted by substrate structure, such as heterogeneous pore networks, or selfimposed by reactant segregation. The classical differential equations (DEs) of chemical reaction assume perfect mixing among reactants, and this assumption is transmitted to the most common solution methods. These methods are based on an Eulerian framework, in which space is partitioned into blocks of some size, within which the well-mixed solution is applied. Our recent work aims to rectify the problems associated with the well-mixed assumption in both theoretical and applied settings. First, we examine the effect of sub-grid concentration fluctuations on Eulerian simulations of reaction. Second, we show how a Lagrangian transport and reaction algorithm accounts for the diffusionlimited mixing of reactants. Third, we review the coarse-grained deterministic DEs that include the effects of concentration perturbation growth. This method includes the transport Green function, which can incorporate the specifics of the transport process. Finally, we review the connection between continuum perturbation methods and the numerical (Lagrangian) techniques, providing a map between the new and classical methods to predict chemical reaction rates. Because our methods are derived as scale-independent, virtually any reactive system that suffers from imperfect mixing-whether imposed by underlying structure (i.e., pore networks) or self-imposed by organization of reactants-will benefit from the added realism.
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