Combined Forced and Natural Convection at Vertical Electrodes: Assisting and Opposing Flows

Abstract

Many electrochemical processes involve combined forced and natural (free) convection. The superimposition of velocity gradients and the Lighthill transformation are used to calculate mass‐transfer coefficients for large Schmidt numbers near vertical electrodes where forced and natural convection exist. A distinction should be made between assisting and opposing flows. For assisting flow near a vertical electrode, the third‐order correlation for the Sherwood number is a good approximationwhere subscripts and represent forced and natural convection if each acts alone. For opposing flow, points of zero shear stress are expected along the electrode length, resulting in flow reversals and boundary‐layer separation. An explicit correlation to the limiting forced and natural convection appears more complicated. The combined forced and natural convection near an electrode embedded in a fully developed laminar flow channel is analyzed as well. Again, a distinction should be made between assisting and opposing flows.