Ohmic Potential Drop in Flow‐Through and Flow‐By Porous Electrodes

Abstract

The limiting current analysis has been applied to the flow‐through and planar flow‐by porous electrodes using a recently developed low flow rate mass transfer coefficient correlation. At the limiting current, the maximum ohmic drop in the solution is developed. The flow‐through electrode analysis is identical to that first given by Bennion and Newman. In the flow‐by electrode, the two‐dimensional structure of the potential field is taken into account. It is shown that given a maximum solution ohmic potential drop and reactant conversion, a flow‐by electrode with an aspect ratio is superior to a flow‐through electrode in that the maximum processing rate will always be higher for the range of parameters presented in this work. If the aspect ratio (length‐to‐width) of the flow‐by electrode is large, it is reasonable to assume that the potential field is governed by a one‐dimensional Laplace equation. This simplifying assumption has been examined and shown to overestimate the maximum ohmic potential drop. Given the two constraints mentioned above, a flow‐by electrode will have an optimum aspect ratio which is determined by an economic balance between greater current‐volume of the bed as increases vs. greater pumping and separator (if required) costs which also increase with .