Ari Glezer - US grants

The proposed research focuses on the active control on the origin and evolution of the streamwise vortices in a flat plate boundary layer along an inclined heated surface. Because these vortices play important roles in transport phenomena near the surface, active control of their onset and evolution can become a powerful tool for the manipulation of heat transfer and surface deposition for free convection boundary layers of practical interest, including cooling techniques and manufacturing of electronics chips. The proposed experiments will be conducted in water, and the flow instabilities leading to the formation of the streamwise vortices will be manipulated using mosaics of individually-controlled film heaters flush-mounted on a submerged test surface. An important feature of such manipulation is that the ensuing flow structures are extremely repeatable in time and space, thus allowing for detailed measurements and flow visualization studies that are phase-locked to the excitation wave-form. Of particular interest are the flow mechanisms, associated with the evolution of the streamwise vortices. Spanwise interactions of these vortices appear to be a precursor to the development of a secondary instability that is followed by rapid transition to turbulence. High-resolution measurements of cross-stream and spanwise time-dependent temperature distributions will be obtained using rakes of miniature cold-wire temperature sensors, and the flow will be visualized using sensitive double-pass Schlieren system. An important aspect of the proposed work is the measurement of global and of planform distributions of heat flux from the test surface to the adjacent fluid. Of particular interest is the incremental change in heat transfer between the forced and unforced flows. At the later stages of this research, the surface actuators will be used to control suppression or enhancement of the longitudinal vortices.

ABSTRACT CTS-9528642 GLEZER GEORGIA INSTITUTE OF TECHNOLOGY A key problem in manufacture of multi-layered printed circuit boards is rapid and uniform deposition of copper on inner surfaces of plated "through-holes." For conventional boards (in which all interconnects are by means of through- holes) as well as boards also using surface-mount technology, the trade-off between plating speed, uniformity, and deposit ductility is such that acceptable yields are achievable only at the cost of reduced speed, requiring large capital investment and in-process inventory costs. For holes of higher aspect ratio in future boards, incremental modification of the existing process will be incapable of providing the desired uniformity at acceptable processing rates. This project consists of a fundamental study of the fluid mechanics and mass transfer of a radically new approach to plating high aspect ratio holes. The key idea is to operate rotating screw electrodes (RSEs) in through-holes of submerged boards. The RSE generates radial, azimuthal, and axial flow, leading to much more effective mass transfer into and within the hole than is possible using conventional technology. Experiment shows the thickness of the resulting copper deposit has much greater axial uniformity than is achieved using the popular oscillating board technique, which establishes time-periodic Poiseuille flow in the hole. Flow modification by an axial pressure gradient, whose magnitude will be chosen to give flow reversal, will also be considered. This will provide countercurrent mass transfer between oppositely directed portions of the flow and suppress formation of cation-depleted boundary layers in the central section of the hole. This approach will lay the foundation for industrial evaluation and development of an improved plating process for high aspect ratio through-holes currently being developed. The results will also have implications for enhancing heat and mass tra nsfer in other applications.

Abstract- Glezer CTS- 9724471 Micromachining facilities and diagnostic equipment are consolidated and expanded into an integrated facility for development and testing of robust fluidic sensors and activators. Equipment acquired includes a large-area alignment system, a parylene deposition system, a hot vacuum press, a precision machining apparatus, a laser vibrometer, a particle image velocimetry system, and microscope/video systems. Initial application will be in research on thermal management, modification of aerodynamic surfaces, thrust vectoring, hybrid activators, real-time viscosity measurement, and mixing in combustion.

Theoretical understanding and experimental creation, characterization and utilization of fluid jets of nanoscale dimensions present significant scientific, engineering and technological challenges. These challenges originate from fundamental issues pertaining to the physical properties of liquids whose dimensions approach the molecular scale, as well as problems related to the design, creation and characterization of liquid jets with such reduced sizes. The interdisciplinary program developed at the Georgia Institute of Technology, that combines researchers from the schools of Physics, Electrical & Computer Engineering and Mechanical Engineering, aims at developing, implementing, and applying theoretical and experimental tools that will allow systematic investigations targeted at gaining deep insights into the microscopic mechanisms underlying the formation of nanojets and governing their stability, as well as leading to the design, fabrication and application of nanojets. Applications of nanojets are envisaged in diverse future nanoscale technologies, including: surface patterning, electronic circuit printing, coating, fiber spinning, and trans - membrane needless injections. The theoretical techniques that will be employed in this program include large-scale computer-based atomistic simulations, as well as continuum hydrodynamic modeling modified to include size-dependent fluctuations, with a focus on the development of reliable methodologies of predictive capabilities. The critical materials issues and outstanding fabrication and characterization challenges, will be addressed through the development and adaptation of imaging techniques, including electron microscopy and atomic-force-microscope imaging of nanojets during flow, as well as post-deposition analysis of nano-printed features and applications of nano-structural fabrication techniques and detection methods that are at the frontiers of nanoscale engineering and detection capabilities. For further information, please contact: Professor Uzi Landman, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332-0430 e-mail: uzi.landman@physics.gatech.edu(404-894-3368) The proposal was submitted in response to NSF 02-148 (Nanoscale Interdisciplinary Research Teams) and has been funded by the Thermal Transport and Thermal Processing Program and the Fluid Dynamics and Hydraulics Program of the Chemical and Transport Systems Division.

CBET-0828874
Yoganathan

This research program focuses on developing an attractive way to mitigate the adverse effects of high shear stress in cardiovascular hardware by investigating miniature, surface-integrated passive flow control elements (e.g., vortex generators, riblets, dimples, etc.). Blood damage caused by flow shear can cause thromboembolic complications that seriously limit the performance of a broad range of cardiovascular hardware including prosthetic valves, bypass pumps, and assist device. In particular, recent work with bileaflet mechanical heart valves has emphasized the significant risk of thromboembolic complications when blood elements are subjected to non-physiological hemodynamic shear stresses. Currently, patients with mechanical heart valves must undergo lifelong anti-coagulant therapy as a preventive measure against thromboembolic complications, but at an increased risk of hemorrhage and other secondary complications. An attractive way to mitigate the adverse effects of high shear stress in cardiovascular hardware is to use miniature, surface-integrated passive flow control elements (e.g., vortex generators, riblets, dimples, etc.) to alter the internal velocity distributions at known critical areas of high shear and thereby directly minimize these stresses. These passive flow control elements which in many cases have been bio-inspired, manipulate and manage secondary vorticity concentrations within the flow and thereby enhance cross stream mixing, momentum transfer, and alter local velocity and shear stress distributions. Although preliminary work demonstrates the viability of the approach, further exploration and optimization of various passive flow control configurations is necessary to take the technology to the next level. The broader impact of this research program is the development of a new design paradigm or technology, applicable to any cardiovascular hardware, based on the flow control principles developed here. The proposed work will focus on a simple cardiovascular test-bed system comprised of an idealized heart valve fitted with passive vortex generator arrays and other configurations. Different passive flow control configurations (rigid, flexible, geometries) will be explored and optimized. The effect of the secondary flow (streamwise vorticity) induced by the passive vortex generators on the momentary turbulent jet that forms when the leaflets close will be investigated in the pulsatile flow loop facility using highresolution, phase-locked particle image velocimetry (PIV). In addition to fluid mechanical evaluation, the pro-coagulant properties of optimized configurations of passive flow control configurations will be characterized and compared to a baseline flow in the absence of flow control. Similar to the recent preliminary blood investigations at Georgia Tech, the proposed blood studies will focus on measures of blood coagulation, platelet activation, and hemolysis. The study will directly involve participating Georgia Tech graduate and undergraduate students. Particular emphasis will be placed on collaboration and testing in configuration of practical interest.

This project is jointly funded by the Thermal Transport Processes (TTP) Program, the Biomedical Engineering (BME) Program, and the Fluid Dynamics (FD) Program, all of the Chemical, Bioengineering, Environmental, and Transport Systems (CBET) Division within the Directorate for Engineering (ENG).

0933506
LaPlaca

The ability to grow and manipulate cells in culture is crucial to understanding basic mechanisms of both normal and disease processes. Three-dimensional thick neural cultures, in particular, mimic brain tissue, but are limited by the lack of a blood supply to deliver nutrients and remove waste. There is a critical need to develop new technology to address this need and produce valid brain tissue models. The intellectual merit of this interdisciplinary research lies in the engineering of a new culture model that includes the major cell types in the brain: neurons, astrocytes, and microglia, together with a highly controllable microfluidic system that perfuses nutrients throughout the culture and permits waste removal and sampling of the cell culture media during periods of both normal conditions and cell injury. Several new innovative elements will be incorporated: 1) include inflammatory cells (microglia) to create a more realistic cell model; 2) introduce a unique, ultrasound-based injury model to produce local injury within the culture; and 3) incorporate microfluidics for perfusion and sampling. Thus, the overall objective is to create a robust and complex neural tissue equivalent that will faithfully represent brain and to investigate the role of microglia following inflammatory triggers. In Task 1, the most appropriate building blocks are chosen to create a novel, complex 3-D neural system for studying inflammation. In addition, microfluidics will be integrated to include perfusion and sampling capabilities. Furthermore, a new traumatic injury model will be developed, providing a means for detailed study of injury mechanisms using highly controllable and tunable methodology. In Task 2, the role of the microglia in the injury response will be tested, as cytokines released from injured microglia are hypothesized to increase cell death. This research is highly significant, as robust culture tools that incorporate multiple cell types and microfluidic perfusion and sampling offer unprecedented levels of spatial and temporal control for determining mechanisms of both normal and injured cells. The broader impact of this research direction will be the development of extremely novel neural tissue equivalents that can be used for numerous applications. It is expected that the next generation of culture systems realized by this approach will revolutionize the way neural cell culturing is done, as the complex interactions among cell types are considered and microcirculation is mimicked through microperfusion. Three-dimensional tissue models with these capabilities will push forward the translation of basic science discoveries for industry, government, and medical breakthroughs. The technical findings will be shared with university, government, and industry researchers with emphasis on collaboration and ultimately having an impact on those affected with traumatic injury or other neurological disorders.

1357813
Glezer

The rate of consumption and withdrawal of water for use in power plant cooling systems has become untenable in light of limited water supply and cost, as well as regulatory restrictions, and environmental concerns. However, the effectiveness of dry air cooling of current, conventional condenser systems has been hindered by the high thermal resistance and poor air thermal capacity of the cooling air. It is clear that in order to enable an appreciable decrease in water consumption for power generation, the heat transfer between the condensing steam and the air-side medium must be significantly enhanced. Earlier attempts to improve the air-side heat transfer focused on the addition of surface features (dimples, etc.) on the cooling fins with limited success and significant increase in fan power. The proposed program overcomes the limits of air-side heat transport by exploiting interactions between the cooling air flow and miniature, autonomously-fluttering reeds (AFRs) to induce the formation and advection of small-scale vortical motions near the condenser fin surfaces. A unique aspect of this approach is that reed flutter is generated by harnessing mechanical energy from the embedding cooling air flow at exceedingly low penalty in pressure losses. These low-cost thin reeds can be tailored for different regions of the condenser and fabricated either integral to the external condenser surfaces or as drop in retrofit assemblies for existing condensers. The reed assemblies are easy to install and maintain without plant level infrastructure modifications. Preliminary heat transfer enhancement and pressure drop analyses coupled with condenser designs and power plant simulations have shown that air-cooled condensers using AFR technology can increase plant efficiency while significantly reducing water consumption compared to wet cooling.

The research program will focus on enabling advances in thermoelectric power plant condenser technology to overcome current limits of cooling by dry air and thereby significantly reduce water usage for evaporative cooling. The present approach overcomes the limits of air-side heat transport by exploiting interactions between the cooling air flow and miniature, autonomously-fluttering reeds (AFRs) to induce the formation and advection of small-scale vortical motions near the condenser fins. A unique aspect of this approach is that reed flutter is generated by harnessing mechanical energy from the embedding cooling air flow at exceedingly low penalty in pressure losses.

The program encompasses integrated experimental/modeling/numerical investigations that will focus on the fundamental knowledge needed to implement, design, and optimize the use of the AFRs, and demonstrate their efficacy in improving the heat transfer characteristics of finned air-side passages of condensers in power plant configurations and operating conditions. The research at Georgia Tech will focus on experimental investigations of the heat transfer characteristics enhanced by the AFRs along with the modeling, design, and testing of novel condenser configurations enabled by the AFR technology. Johns Hopkins University will focus on CFD investigations of small-scale heat transfer and performance evaluation and optimization of AFR-enhanced condenser configurations.

Small-scale heat transfer enhancement by AFRs was recently demonstrated in air-cooled heated ducts at Georgia Tech with significant heat transfer enhancement. These low-cost thin reeds can be tailored for different regions of the condenser and fabricated either integral to the external condenser surfaces or as drop in retrofit assemblies for existing condensers. The reed assemblies are easy to install and maintain without plant level infrastructure modifications.