Fluid Mechanics Seminar: Ali Mani

Electrochemical interfaces, e.g., the interface of an aqueous electrolyte with a charge selective surface such as an electrode or a membrane, are host to a range of physical phenomena involving ion-transport, electrostatic interactions, and fluid flow. The equations governing these disciplines are the Nernst-Plank, Poisson, and Navier-Stokes, which have been well-established for more than a century. Analytical solutions to these equations have contributed to the understanding of various interfacial phenomena such as electric double layers, electro-osmosis, and diffusion boundary layers. However, only very recently direct numerical solutions to these equations became available.

In this presentation, we consider voltage-driven ion transport from an aqueous electrolyte to an ion-selective membrane as a canonical setting to study fluid dynamic effects induced by ion transport near electrochemical interfaces. We will present results from our numerical simulations demonstrating that beyond a threshold voltage such interfaces trigger hydrodynamic chaos with features similar to turbulent boundary layers, despite their low Reynolds number. Structures with scales from sub-millimeter down to tens of nanometers can be formed as a natural result of these hydrodynamic effects. These flow structures are shown to impact mixing and enhance net ion transport well beyond nominal diffusion-controlled processes.

While predictions of these simulations are consistent with recent experimental observations, simulations allow for non-intrusive capture of fine spatiotemporal details in these flows. We will demonstrate the need for the development of specialized algorithms for computation of these systems similar to the tools that have been traditionally used for the simulations of turbulent boundary layers. Such calculations require resolving a wide range of scales using unsteady solvers and often demand massively parallel computational resources. By presenting various examples, we will discuss how the development of high-fidelity computational tools can lead to fundamental understanding of complex effects in electrochemical interfaces and facilitate their design and optimization.

Biography: Ali Mani is an Assistant Professor in the Department of Mechanical Engineering at Stanford University. He received his Ph.D. from Stanford University in 2009, and after a period of postdoctoral Research in MIT Chemical Engineering, he joined Stanford as a Faculty in 2011. His research is broadly focused on fluid dynamics problems that involve strong coupling with mass-transport phenomena and commonly involve turbulence or chaos. Current themes in his research include turbulent multiphase flows, bubbly flows, superhydrophobic surfaces, and fluid dynamics in electrochemical systems with applications in microscale engineering.