Study on Marangoni- and buoyancy-driven convection in smaller Reynolds number flow field of electrochemical machining

Abstract

In order to study the Marangoni- and buoyancy-driven convection in smaller Reynolds number flow field, a new electrochemical machining model was established by coupling various physical fields, in which the machining gap was defined as 20 mm and the electrolyte conductivity was equal to 8.74 S/m. Through the numerical simulation and experiments, the mechanisms of convection formation, diffusion and instability were investigated. The results indicated that the convection cells had a strong correlation with the current density, and the convection driven by buoyancy and Marangoni forces existed in the flow field. With the accumulation of the heat in the processing area, the transition region gradually became the main channel for the heat transfer. The convection cell gradually changed from a stable and symmetrically distributed structure to an annular convection structure, when the processing voltage exceeded the critical voltage (12 V). The convection cells in the processing region were mainly driven by the Marangoni force, which eventually formed the Marangoni convection. The convection cells near the upper surface of the electrolyte were induced by the buoyancy force, which formed the buoyancy convection. The convection cells in the transition region were gradually compressed and destroyed by the progressively increasing buoyancy effect and the bubble flow. Near the anode-electrolyte interface, the boundary layer thickness of the velocity was more important than the boundary layer thickness of the thermal, and the convection transportation was significantly larger than the diffusion transportation. These characteristics provide application potential for the thin film self-assembly process in ECM.