A study of roughness and mass transfer enhancement for the rotating cylinder electrode

Abstract

It is well established that enhanced mass transfer occurs at a rotating cylinder electrode operated in the turbulent regime when cathodically deposited metal grows in a rough powdery or dendritic manner. In the absence of quantitative data for the degree of roughness and the consequent increase in the friction factor, such enhancement has been expressed empirically as an increase in the power exponent of a simple mass transfer relationship K L = constant × U n where n is normally about 0.7 in turbulent flow for a smooth electrode. By using cylinder electrodes of known induced roughness, which can be characterized by a true surface area, topography etc., it is possible to distinguish between the effects of increased surface area and microturbulence, whence it becomes possible to recognize and devise optimal methods of increasing the surface roughness in order to maximize mass transfer. For the V-grooved cylinders investigated, the saturated or maximum enhanced mass transfer was correlated according to the power law relationship where n varied between 0.51 and 0.58. For six such cylinders the average increase in mass transfer at a high velocity, or degree of enhancement, was 80% relative to a smooth cylinder.