Mixing studies related to the cleaning of molten aluminium

`Molten aluminium is traditionally "cleaned" by a chlorine-based fluxing gas. This gas also has to provide the motive power for mixing. Recently, mechanical agitation with solid fluxes has been considered as a replacement for environmental reasons. Here, these two methods of mixing are compared using particle image velocimetry (PIV), decolourisation for homogenisation and power measurement for comparison of efficiencies. A geometrically scaled-down vessel was used, with air to mimic "chlorine" fluxing and with water as the working fluid. At equivalent mean specific energy dissipation rates, (ε) over bar (T), maximum velocities are higher and mixing times are shorter with an impeller. Ibis improved performance is achieved with the impeller without causing surface gas entrainment, the latter being detrimental to fluxing.