Measurement of mass exchange processes and coeffic

Authors: Emmanuel Mignot Wei Cai Juan Ignacio Polanco Cristian Escauriaza Nicolas Riviere

Publish Date: 2016/11/19

Volume: 17, Issue: 3, Pages: 429-448

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Abstract

Lateral cavities are major storage zones in riverine environments for which the mass exchanges with the main stream strongly impact the characteristics of the habitat in these dead zones An experimental work is presented here with a controlled main stream and a connected openchannel lateral cavity to assess the processes responsible for these exchanges and to quantify the exchange capacities In a first step the measurements of passive scalar transport allow us to identify the physical processes involved in the exchange of mass from the main stream and its spreading within the cavity In a second step the quantitative mass exchange coefficient representative of the exchange capacity is measured for 28 flow and cavity configurations The sensibility analysis to the governing parameters proposed by the dimensional analysis then reveals that changing the geometric aspect ratio of the cavity does not affect the exchange coefficient while increasing the normalized water depth or decreasing the Reynolds number of the main stream tend to increase this coefficient Indeed these parameters modify both the growth rate of the mixing layer width at the interface and the amplitude of the alternating transverse velocity across the interface thus affecting the exchange capacities from the main stream to the cavity

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