Instantaneous Measurements of Molecular Mixing in High Reynolds Number Shear Flows

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CTS-9423280 J. C. Dutton & Robert Lucht University of Illinois This research seeks to develop and apply a new technique for quantitative measurements of the structure of high Reynolds number gaseous shear flows, including the capability of measuring the extent of mixing at the molecular level. The extent of mixing at the molecular level in shear flows will be measured instantaneously by using two different lasers and two different lasers and two different cameras to excite and then detect laser-induced fluorescence (LIF) from nitric oxide (NO) and acetone simultaneously. NO will be added as a seed species to air in the other stream. In pure nitrogen, the NO LIF quenching rate is orders of magnitude smaller than the quenching rate in air. Consequently, if the two streams mix at the molecular level to even a small extent, the NO LIF signal will virtually disappear. The acetone LIF signal is proportional to the acetone number density in the fluid volume, whether or not the fluids have mixed at the molecular level. The simultaneous NO-acetone LIF imaging technique will allow quantitative measurement of the fraction of the seeded fluid that has been macroscopically stirred with the unseeded fluid, as well as the extent to which the streams have mixed at the molecular level. Quantitative measurement of molecular mixing are of tremendous importance, particularly in chemically reacting systems where mixing of the fuel and oxidant streams at the molecular level is required for chemical reaction. As an important practical example, fundamental understanding of mixing at the microscale as well as the macroscale is necessary for accurate calculation of pollutant formation in flames.