Abstract:In the aluminum electrolytic process, alumina was dissolved in the electrolyte under the control of both heat and mass transfer mechanism. Heat transfer control model, mass transfer control model and the shrinking core model of alumina dissolution were established, Based on the OpenFOAM open source software platform, alumina dissolution solution module was set up by the custom code. Numerical simulations of the dissolution of alumina particles under the two mechanisms were conducted. The results show that under the control of mass transfer mechanism, the mass dissolution rate and the varying gradient of the mass dissolution rate of alumina particles reduce with decreasing the particle size. Under the control of heat transfer mechanism, the mass dissolution rate decreases with decreasing the particle size, while the varying gradient of the mass dissolution rate shows little change. In order to distinguish the dominance of the heat transfer or mass transfer control mechanism, the definition and judgement of the critical diameter were put forward. Considering the dissolution process of alumina particle is governed by mass transfer as well as heat transfer mechanism together, the critical diameter is 560 μm. The dissolution of alumina particles with the size of less than 560 μm is governed by mass transfer mechanism, while the dissolution of alumina particles with the size of more than 560 μm is under the control of the heat transfer mechanism.

Key words: aluminum reduction; alumina dissolution; mass transfer mechanism; heat transfer mechanism; critical diameter