ABSTRACT CTS-9706824 Vijay Modi/Columbia U. Accurate estimation of mass flux in impinging flow systems is important to wet chemical processes such as water rinsing, photoresist development, electrodeposition and electrochemical machining. The physical system of interest is a confined submerged slot jet impinging normally on a mass transfer surface under turbulent flow conditions. The effect on hydrodynamics and mass transfer of small scale structures on the impingement surface, typical in MEMS device fabrication is not understood. Experimental measurements of mass transfer will be carried out for both flush surfaces as well as surfaces with structures ranging from 5 to 500 microns in size. The location and aspect ratios of the structure will be varied as well. Flush surface a single sensor will provide local mass transfer rates on the impinging surface. For the smallest structure size, i.e. 5 microns, both single and multiple patterned structures will be considered. Mass transfer measurements will be made by the electrochemical method, where ferricyanide ions are reduced on one or more closely-spaced platinum electrodes at a rate controlled by mass transfer to the surface. An existing finite volume code will be utilized for modeling the incompressible turbulent fluid flow and mass transfer. A major question that needs to be addressed is: what is the appropriate model for the turbulent eddy diffusivity near the wall at the high Sc applications common to wet processing? Since one single model that is valid for all turbulent flows are unlikely to emerge, the present effort will develop a model for the particular flow system of interest here. The flush surface experimental data will aid in developing such a model. This model will be implemented in the numerical solvers. Once validated the ability of such a model to aid predicting the mass transfer to a surface with microstructures will be established.
