The Environmental Fluid Dynamics Lecture Series Presents a Seminar   The Environmental Fluid Dynamics Lecture Series Presents a Seminar Mixing and Unmixing in Natural Flows: Qualifying the Throttle on Chemical Reactions Dr. David Benson Associate Professor Director, Hydrologic Science and Engineering Program Colorado School of Mines Golden, CO Tuesday, January 26, 2016 127 Hayes-Healy 11am-12noon Analytic expressions for chemical reaction rates only exist for end-member cases: perfectly-mixed or maximally unmixed. The former rarely applies for large-scale systems such as oceans, atmospheres, and aquifers. Furthermore, a system that starts at one end-member or the other will tend to migrate toward a state of intermediate mixing for which rate expressions are lacking. I will show work in progress on assessing upscaled reaction rates in quiescent systems where mixing degenerates from self-segregation of chemical constituents, as well as systems in which mixing is enhanced through deformation (by stretching and/or shear). Our work is derived from a Lagrangian viewpoint, so that the enhancement of reactions induced by fluid deformation by calculating the change to the co-location probability of nearby particles in a flow field, which is linear with total reaction probability for thermodynamically fast reactions. In a numerical simulation of aquifer flow (Figs. 1a and 1b), the enhanced reaction at any point (measured by the co-location density) is best correlated to the largest eigenvalue of Cauchy-Green (deformation) tensor (Fig. 2). Fig. 1 a&b Fig. 2 a&b