Three-dimensional CFD simulation of bubble-melt two-phase flow with air injecting and melt stirring

Highlights: → Gas-metallic turbulent flow induced by an impeller with an inclined shaft was studied. → A two-fluid model incorporated with the multiple reference frames method was used. → The bubble number density function was accounted for bubble breakup and coalescence. → Effects of gas flow rate and impeller speed on bubble size distribution were studied. - Abstract: This paper reports on progress in developing CFD simulations of gas bubble-metallic melt turbulent flows induced by a pitched-blade impeller with an inclined shaft. Foaming process of aluminum foams, in which air is injected into molten aluminum composites and the melt is mechanical stirred by the impeller, has been investigated. A two-fluid model, incorporated with the Multiple Reference Frames (MRF) method is used to predict the three-dimensional gas-liquid flow in the foaming tank, in which a stirring shaft is positioned inclined into the melt. Locally average bubble size is also predicted by additively solving a transport equation for the bubble number density function, which accounts for effects of bubble breakup and coalescence phenomena. The computed bubble sizes are compared with experimental data from our water model measurement and reasonable agreements are obtained. Further, simulated results show that the volume averaged total and local gas fractions are generally increased with rising impeller speed and gas flow rate. The local averaged bubble size increases with increasing gas flow rate and orifice diameter and decreasing liquid viscosity, and decreases also with rising rotation speed of the impeller.