The characterisation of electrochemical reactors with impressed flow

The reaction environment and its relationship to engineering parameters has a bearing on the output of an electrochemical cell. Mass transfer, dispersion and distribution of reaction have been studied in various cell geometries over a range of operating modes. The problem of dispersion modelling in parallel channel laminar flowswhere zones of mixing occur usually necessitates working in the Laplace plane unless simplistic assumptions are made. The inherent advantages and disadvantages to both approaches are discussed in the light of data obtained from aqueous electrolyte flows (and gas/liquid mixtures) in theReynolds range 25-1000. Mass transfer, pressure effects and mixing in cells with rotating electrodes are examined in the Bipolar Pump Cell, anovel cell designed for electrosynthesis, and the Rotating Electrolyser where separation of anolyte and catholyte streams can be effected by hydrodynamic means alone. In a complex electrochemical system, the magnesium/silver chloride seawater battery, the distribution of reaction due to gas evolution and electrolyte conductivity effects have been studied in the pressure range 1 to 6 bar(g). The experimental methods include the use of hydrodynamic model cells together with the 'marker pulse' technique to measure dispersion, laser Doppler anemometry to establish velocity profiles, active electrodes incorporating micro-electrodes for mass transfer studies and segmented working cells coupled to multiple local data acquisition. It is shown that laminar flow in parallel channels can be treated as partially segregated and that rotation in practical electrolysers allows greater control over mass transfer and mixing. The interactive nature ofoperating variables is seen to influence local reaction conditions with consequences on overall battery performance.