https://doi.org/10.15255/KUI.2002.011
Published: Kem. Ind. 52 (1) (2003) 1–8
Paper reference number: KUI-11/2002
Paper type: Original scientific paper

Electrochemical Reactor with Three-Dimensional Electrode: Part II Natural Convection

A. Meštrović-Markovinović and T. Todorović

Abstract

A limiting current technique was used for the measurement of the natural convection mass transfer rate in a vertical flow-through pipe reactor with three-dimensional electrodes. The electrode consisted of metallic sphere particles of varying diameter, arranged in 1-5 layers. The electrolyte was an equimolar solution of varying potassium ferri-ferro cyanide concentrations in 0.5 mol dm-3 NaOH. The change in the limiting current was monitored as dependent upon the size of the particles, the number of layers, and the concentration of the electrolyte. Investigations of natural convection through a porous vertical layer have shown that mass transfer via natural convection takes place only when the driving force (the difference in densities) is large enough to overcome the resistance to flow through the interspaces between spheres, and the forces of friction and inertion which oppose the flow. Thus, the depth of flow penetration via natural convection depends on electrolyte concentration and the size of the interspaces. With an electrode that is composed of spheres of diameter dk = 2.65 and electrolyte of concentration c = 5.5 mol m-3, mass transfer via natural convection occurs only through one layer of spheres. With an electrode that is composed of spheres of diameter dk = 4.35 and the same electrolyte concentration, mass transfer via natural convection takes place through four layers of spheres. At concentrations c ≥ 30 mol m-3 mass transfer via natural convection takes place through all investigated layer independent of the size of the spheres, and the intensity increases with increasing number of layers. Experimental results under natural convection are in accordance with the relation: Sh=0,016(Gr Sc)0,48 which holds true in the entire investigated region: 105

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Keywords

porous electrode-packed bed, mass transfer, natural convection