Modelling natural convection at complex surfaces and solid bodies using electrochemical techniques and flow visualisation

Abstract

Since the review by Wragg [Journal of Applied Electrochemistry, 21 (1991) 1047] of more than 15 years ago there has been a considerable research output involving the use of combined electrochemical and flow visualisation techniques to investigate complex flows in natural convection situations. This paper reviews recent work involving electrode geometries and orientations such as vertical cylindrical electrodes of varying aspect ratio, down pointing and up pointing pyramidal electrodes, down facing horizontal circular surfaces with different edge conditions, isosceles triangular surfaces of various inclinations, long narrow upward facing linear tracks, open upward facing cavity electrodes, upward and downward facing truncated cones, and inclined disks with either single or both sides active. This constitutes a wide range of experimentation in which new insights into data treatment and correlation have been obtained. We have used approaches taking account of the differing behaviours of the single sides of three dimensional objects and computing interference factors taking account of flow interactions. Some highly successful illustrations of data correlation for extremely complex situations are demonstrated. Flow visualisation for most of the above mentioned situations have been obtained using schlieren photography which has provided good illustrations of flow structure occurring at single faces of objects and in complexly interacting flows. In addition we have combined some flow visualisation sequences with monitoring of the current-time relationships at the onset of convection to illustrate flow development phenomena from the onset of convective instabilities to the achievement of steady state conditions.