Flow Cell Characterisation: Flow Visualisation, Pressure Drop and Mass Transport at 2D Electrodes in a Rectangular Channel

Abstract

Aiming to demonstrate the importance and facility of characterising the reaction environment in new commercial laboratory-scale flow cells, fluid flow, pressure drop and space averaged mass transport coefficient were studied in the C-Flow® Lab 5 × 5 cell. A flow-by configuration with smooth, planar electrodes in a rectangular channel was used. Electrolyte mean linear velocities of 2 to 10 cm s−1 past the electrode surface and channel Reynolds numbers of 53 to 265 were considered. The effect of a turbulence promoter next to the working electrode was evaluated. Flow distribution was explored by a qualitative flow visualization study, while the relevance of pressure drop was shown by measurements over the flow channel and the whole cell as a function of mean linear velocity. The electrochemical performance was quantified from the limiting current, permitting the determination of the mass transport coefficient at the electrodes over the same range of flow rates. Reactant conversion in the batch recirculation mode and normalised space velocity were predicted from the electrochemical plug flow reactor design equation. Results were compared to well-characterised electrochemical flow reactors found in the literature. The significance of characterisation techniques and basic reactor models during the development of new processes is emphasised.