THE EFFECTS OF A VARIETY OF WALL OBSTRUCTIONS ON LOCAL MASS-TRANSFER IN A PARALLEL-PLATE ELECTROCHEMICAL FLOW CELL

This paper demonstrates the effects on local mass transfer of placing a variety of partial obstructions in the form of fences or steps ( arr anged in single or multiple configurations) on the walls of a parallel plate electrochemical flow cell. For the wall on which the fence is p laced, a plot of the position of mass transfer relative to an obstruct ion against the Reynolds number for different fence heights shows that , for each fence, the distance to peak position initially increases wi th the Reynolds number, but tends to decrease al higher Reynolds numbe rs. For the wall opposite to the fence, a pronounced peak immediately opposite the obstruction, corresponding to a position of maximum veloc ity, and a second downstream peak, corresponding to a recirculation/re attachment zone, were identified. A correlation of the peak Sherwood n umber as a function of the Peclet number for all fence heights and als o for a backward-facing step was compared with data of other workers. The numerical prediction of flow reattachment to the walls produced ex cellent agreement with the positions of peak mass transfer for both th e fences and the step, but agreed less well in terms of magnitude. (C) 1997 Elsevier Science S.A.