Fundamental changes in in situ air sparging flow patterns

Two types of gas-phase flow patterns have been discussed and observed in th e in situ air sparging (ISAS) literature: bubble flow and air channels. A c ritical factor affecting the flow pattern at a given location is the grain size of the porous medium. Visualization experiments reported in the litera ture indicate that a change in the flow pattern occurs around 1 to 2 mm gra in diameters, with air channels occurring below the transition size and bub bles above. Analysis of capillary and buoyancy forces suggests that for a g iven gas-liquid-solid system, there is a critical size that dictates the do minant force, and the dominant force will in turn dictate the flow pattern. The dominant forces, and consequently the two-phase flow patterns, were ch aracterized using a Bond number modified with the porous media aspect ratio (pore throat to pore body ratio). Laboratory experiments were conducted to observe flow patterns as a function of porous media size and air flow rate . The experimental results and the modified Bond number analysis support th e relationship of flow patterns to grain size reported in the literature.