A Quantitative Mixing Analysis Using Fluorescent Dyes

Copyright © 1995 by J. Coppeta. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. Abstract In this paper a method of quantifying fluid mixing using the fluorescence intensity of fluorophors in aqueous solution is presented. The general technique involves ratioing optically separable fluorescence from two fluorescent dyes. The resulting ratio normalizes for laser intensity distribution and any laser reflections. By properly selecting the fluorescent dyes, fluorescence ratios can be used to either measure the concentration of a passive scalar or temperature fields. In this study, fluorescence ratios were used to quantify the hydronium ion concentration of mixing fluids in a two dimensional plane. This was accomplished by temporally and spatially synchronizing two CCD cameras to simultaneously image laser induced fluorescence. Single and multi-dye systems were examined for their accuracy in predicting mixing and of the dye systems examined, a fluorescein rhodamine B solution proved to be the most accurate. Using this dye system, the fluorescence ratios were found to vary under 1 standard deviation for a 2.5 fold change in laser power. A standard error of under 6% of the mean fluorescence ratio was typical. This system was demonstrated by measuring the mixing in an axis-symmetric turbulent jet with an Reynolds number of 9,000. Finally, this technique was shown to be capable of measuring temperature fields.