(466b) Hierarchical Modeling of Transport Phenomena In Porous Media: A Perspective and Payatakes' Contributions

Hierarchical modeling can have a central role in the field of porous materials and their applications in a multitude of technological fields. During the last 30 years, the scale of observation but also of theoretical modeling and simulation has expanded to cover practically all sizes from nanopores to miles of geological material. Computational techniques can guide investigations across scales in a well-structured fashion and are nowadays recognized as indispensable -in combination with sufficiently accurate experimental techniques- in a number of porous material design and synthesis challenges, including new or modified molecular sieves, porous membranes with controlled hydrophilicity, tailored pore networking within otherwise dense materials etc. The breakdown of the continuum approximation in nanopores calls for molecular or pseudo-molecular approaches that can handle rarefied flows. Application of such ensemble techniques (e.g., Direct Simulation Monte Carlo [1]) to realistic length scales necessitates switching to faster mesoscopic techniques (e.g., lattice-Boltzmann) without sacrificing significant degrees of freedom, provided that an effective, Knudsen number dependent viscosity is employed [2]. Specific examples from the membrane separation field can serve to demonstrate the interweaving of techniques into a bottom-up methodology for process intensification and improvement of efficiency indices. Payatakes' contributions at different stages of such a general hierarchical approach involved several pioneering steps in the sequence of pore structure recognition, simulation of transport phenomena in pore models, and study of particulate systems at all levels from the individual particle level to mesoscopic and, eventually, macroscopic models and experiments. His commitment to quality research and his true passion for revealing the rich phenomena that take place in the interior of porous media have inspired a great number of scientists in the field but also in emerging interdisciplinary areas.

[1] G.A. Bird, Molecular Gas Dynamics and the Direct Simulation of Gas flows, Clarendon Press, Oxford, 1994.

[2] V. Michalis, A.N. Kalarakis, E.D. Skouras, and V.N. Burganos, ?Rarefied Fluid Viscosity from DSMC Calculations in Nanosized Channels?, Microfl. Nanofl., in press (2010).