Mass transfer caused by gravitational instability at reactive solidliquid interfaces
Mass transfer in porous media has been investigated experimentally. In this paper, we present a visualization technique and discuss the behavior of a substance which transfers under the influence of gravity and reacts with the surface of porous media. Mass transfer by the reaction with porous media was demonstrated by means of electrochemical deposition experiment on particulate beds with complex structures. A copper plate (anode) and a stainless steel particulate bed (cathode) were, respectively, placed at the upper and bottom side of a thin vertical cell which was filled with copper sulfate solution. After the application of electricity, cupric ion which is provided from the copper plate to the solution transfers under the influence of gravity and it is consumed by deposition at the particulate bed. The behavior of ions between the electrodes was visualized by utilizing the infrared absorption characteristics of cupric ion. We observed gravitational instability and convection flow due to concentration gradient of ions in opposite direction to that of gravity, which is formed by reaction at solidliquid interfaces. While downward flow caused by RayleighTaylor instability was observed in the case of flat interfaces, upward flow generated from complex-shaped interfaces was greatly dependent on their geometry. The interaction of these flows resulted in the convection throughout the cell. Consequently, it is found from the results that the gravitational instability significantly varies the transport characteristics and that the reactive interface geometry greatly affects the overall mass transfer.
mass transfer gravitational instability reactive solidliquid interface porous media convection flow