ONSET AND EFFECTS OF INSTABILITIES FROM UNSTABLE STRATIFICATION OF DENSITY ON MASS-TRANSFER IN CHANNEL SHEAR LAYERS AT LOW REYNOLDS-NUMBERS

The onset of mixing in the shear layer located between two coincident laminar streams of different velocity in a thin, ribbon-like channel i s studied. Globally unstable density stratification is employed, which , with certain experimental conditions, results in augmented mixing an d entrainment, and disruption of mass transfer of solid particles comp ared to channels with stable density gradients, and laminar, two-dimen sional flow. The mixing onset boundary is quantified in terms of the R eynolds number, Richardson number, and channel flow rate ratios using a newly developed mixing onset parameter R. The results indicate that unstable density gradients, rather than shear gradients, are most resp onsible for inducing the mixing. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.