Sangtae Kim, Ph.D. - US grants

The purpose of this project is to develop a numerical technique for large-scale simulation of particle motion in suspension with negligible inertial effects. The governing Stokes equations are transformed into a set of Fredholm integral equations of second kind with double-layer densities on the surface of particles and on the boundary of the system. A fast iterative algorithm which makes optimal use of parallel computer architectures is proposed. The technique can be applied to dilute and concentrate suspension flow, non- spherical particles and irregularly bounding walls. It is expected that the research results will provide numerical tools for other researchers in the field of suspension flow, and will be used to interpret various experiments.

This is a three year cooperative study proposed by Dr. Sangtae Kim, the University of Wisconsin, Madison and Professor Huan J. Keh, National Taiwan University supported by the AIT (U.S.) - CCNAA (Taiwan) Cooperative Science Program. This project plans to study the microstructures of electrophoresis. Electrophoresis is one of the most important techniques used in the chemical and biological sciences. Dr. Kim is a leading U.S. researcher in the area of computer simulations and two-phrase flows. Professor Huan J. Ken of the National Taiwan University is a specialist in electrophoresis. Their expertise compliment well and the collaboration is mutually beneficial. This study has been the potential to significantly advance our understanding of the microstructures of electrophoresis.

The object of this proposal is the development of scalable parallel computing algorithms for multi-particle system flow with negligible inertial effects. The particles may have arbitrary shape and roughness. The preparation of the governing equation combined with the use of the advanced parallel computer in suspension rheology. The governing Stokes equations are transformed into a set of Fredholm integral equations of second kind with double-layer densities on the surfaces of particles and on the boundary of the system. The methodology can be applied to dilute and concentrated suspension flow, non- spherical particles and irregularly bounding walls. The emphasis of this proposal is on the computational algorithm rather than physical problems. The goal is to reduce the frequency of inter-processor communication, and to shorten the inter-processor messages, which would increase the overall computational speed. The development of an efficient computational methodology for suspension flow at low Reynolds numbers has a broad range of applications in chemical, pharmaceutical and other industrial processes that use particulate suspensions.

ABSTRACT CTS-9707009 S. Kim U of Wisc-Madison The International Union of Theoretical and Applied Mechanics (IUTAM) 97-9 Symposium Rheology and Computation will be hosted by the University of Sydney, July 20-25, 1997. Participation will be restricted to invited scientists (40 oral presentations, and 100 active participants in the Symposium). The IUTAM Symposia are well established venues for presentation of research results and will attract participants from many disciplines in engineering and applied science departments. The aim of this conference is to bring together an international group of researchers from different fields of rheology. The five themes include: Suspension Rheology Boundary Conditions Molecular Dynamics Computational Methods Experimental Studies In recent years, there has been dramatic progress in various rheology subcommunities, especially with respect to improved efficiency and quality control for the benefit of industry. The goal of the IUTAM conference is to strengthen bridges from complementary perspectives and length scales, ranging from molecular to macroscopic/continuum levels.

This research project is a collaborative effort between the Department of Chemical Engineering and Materials Science (Professors Z. A. Munir and S. Kim) at the University of California, Davis and the Institute of Physical Chemistry (Professor M. Martin) at RWTH Aachen University, Germany. The goal of this research is to provide an understanding of the heretofore-unobserved proton and oxygen transport processes in dense, nanocrystalline oxides, as an example of the nanoscale effect in functional oxides. The investigators' ability to prepare oxides with ultra-small grain size (approaching 10 nm) has opened a window of investigation on this and on related nanometric effects. The aim is to prepare and investigate such materials in dense, bulk form with even smaller grain size ( 10 nm). Observation of the occurrence of low-temperature protonic conductivity in unhydrated yttria-stabilized zirconia and doped ceria, typical predominant oxygen ion conductors, opens a new door on the fundamental issue of a unique behavior of nanostructured electroceramics. Heretofore such a behavior has not been observed since prior attempts to prepare such materials in bulk form had not been successful. The researchers' success was made possible by their unique ability (through a novel pressure assisted field activated sintering method) to prepare highly dense (> 98%), bulk, nanometric oxides with a grain size of < 20 nm. The fundamental questions that arise from their observations include: what is the nature of this protonic conduction? What is the mechanism associated with protonic mobility? Since this phenomenon is only observed in materials with ultra-small grain size, how do grain boundaries play a role in mass and charge transport? In view of observation on thin films, are the role and nature of grain boundaries different when the grains are very small? What, if any, do dopant-generated point defects contribute to the process? The answers to these and related fundamental questions should provide a significant intellectual contribution to our understanding of the nanoscale effect in these functional oxides and stimulate new research in this important area.

The use of stable oxides with mechanical integrity as protonic conductors at low temperatures (even in water at room temperature) has an immense impact on application considerations for protonic conductors. Protonic conductors have an extensive field of application, including their use as hydrogen separators (when used as mixed conductors), or to produce power (when used in fuel cells). They can also be used in electrolysis for hydrogen production, and for reactions to hydrogenate and dehydrogenate organic compounds. Current solid oxide fuel cells require high temperatures (800 - 1000C), a condition that presents material degradation problems, as well as other technological complications and economic obstacles. The economic considerations alone make broad commercialization prohibitive. An effective way to reduce the cost is to reduce the operating temperature without scarifying fast electrode kinetics and high ionic conductivity of the electrolyte, which our results has demonstrated its feasibility. It is to be emphasized that the observed low-temperature protonic conductivity occurs at room temperature without the need to apply a catalyst. The results show that with optimization, viable power generation using water concentration cells at room temperature is a possible goal. An important aspect of the research is the participation and exchanges of graduate and undergraduate students and postdoctoral fellows. In addition to faculty exchange visits, an exchange program for students and postdoctoral fellows is planned. Each graduate student (both from Germany and the US) will go through the entire process from synthesis and consolidation and structural and electrical characterization (at UC Davis) to SIMS determinations (at RWTH Aachen University).