Developing mass transfer for annular swirling decaying flow induced by means of a tangential inlet

Mass transfer between an electrolyte and the inner core of an annular cell fitted with a tangential inlet is experimentally investigated using an electrochemical method. Attention is focused on the influence of the electrode length and position with respect to the tangential inlet to take into account both the development of the hydrodynamic and concentration boundary layers. According to the value of the ratio of the gap width e, to the inlet diameter Φ_e, two kinds of swirling motion are studied: pure swirl flow for e = Φ_e and contraction swirl flow when Φ_e >e. Depending on the geometric factors and the Reynolds number, enhancement in mass transfer of up to 550% is achieved in comparison with that obtained for fully developed axial flow. Two general correlations of the experimental data, taking into account the aforementioned parameters, are proposed for laminar and turbulent swirling flows.