UC Berkeley

The mass transfer through gaps connecting two adjacent channels was investigated as a function of gap geometry and flow conditions. An experiment with a simplified geometry was conducted to aid in the physical understanding and to provide data for validation of numerical computations. The flow loop consisted of two channels with two interchangeable test sections. The inlet Reynolds number in each channel could be independently varied from 4xl04 up to 1x10s. Measurements were performed for seven channel flow rate combinations and eleven gap heights for both test sections. The mass transfer through the gap was calculated from mass flow rate and tracer concentration measurements taken at channel inlets and outlets. Planar and tomographic particle imaging velocimetry, as well as imaging of fluorescent tracer dye, were utilized for select conditions to examine the dynamics of the mixing. Accompanying computations were performed and the results compared favorably with experimental data. For the cases of nearly balanced flow, large coherent structures forming in the gap were observed and exhibited a normalized frequency in agreement with that reported by previous investigators. Over the tested range, the mixing rate as a function of gap height was nominally independent of channel Reynolds number. For significantly unbalanced flow the measured mass transfer approached the one-way mass transfer limit, whereas for larger gaps and closer flow balance the mixing due to coherent structures became significant.