QUANTIFICATION OF MIXING AND MIXING RATE FROM EXPERIMENTAL-OBSERVATIONS

A new measure of mixedness, based on entropy considerations, and a rel ated mixing rate are introduced. It is argued that the time rate of ch ange of the mixedness is proportional to the mixing rate. The new meas ures are applied to experimental observations on an axisymmetric jet a nd an array of jets in crossflow. The concentration field of an axisym metric jet is measured at 10 downstream locations by optical imaging o f Rayleigh scattering from a laser sheet. Mixedness and mixing rate ar e calculated for each of the locations. In agreement with theory, the mixedness of the self-similar jet is constant along the length of the jet. The measures allow us to locate the instantaneous realization tha t is most typical in terms of mixedness and mixing rate. Also analyzed is the mixing of a row of jets injecting fluid into a crossflow, The jets are sufficiently close that there is significant interaction betw een neighboring jets. The mixedness and mixing rate were calculated. W ell-mixed regions have a low mixing rate, whereas poorly mixed regions tend to mix most rapidly. The mixedness and mixing rate allow the ass essment of the effectiveness of different orifice shapes in promoting rapid mixing.