CFD-VOF-DPM Simulation Of Inclusion Removal In Gas-Liquid-Solid Systems

The effective inclusions removal is one of the main tasks of the steelmaking process.Small bubbles in molten steel can capture inclusions and promote the floatation of the inclusions,which is beneficial to the production of clean steel.However,due to the high temperature and invisibility of molten steel,the process of inclusion removal by bubble can only be studied by theoretical analysis and simulation.In the present study,the inclusion removal mechanisms of adhesion removal and bubble wake entrainment of inclusions are studied.Numerical simulation method is used and the volume of fluid(VOF)method is coupled with the discrete particle method(DPM)to carry out the simulation of adhesion removal and bubble wake entrainment with initial bubble diameters of 2 mm,8 mm and 15 mm on the Fluent 16.1 platform.The bubble surface is dynamically tracked by the VOF model,and the inclusions are treated as discrete phase to track their trojectories by the DPM model.The discrete phase was linked to the continuous phases with a two-way coupling through interchange terms in the respective momentum equations.Grid independence was checked by decreasing the mesh size.It was found that good simulation results can be obtained with the mesh size of 0.1 mm(2 mm bubble),0.4 mm(8 mm bubble)and 0.6 mm(15 mm bubble).The accuracy of the model was verified by comparing the shapes of different bubble diameters in simulation with the experimental results,and comparing the rising velocity of 10 mm bubble in the liquid-solid suspension with the simulation results from literature.In order to make clear the influence factors of inclusions removal from molten steel through bubble adhesion and wake entrainment,the influences of inclusion diameter,inclusion density,inclusion number,the surface tension of molten steel,the viscosity of molten steel,the density of molten steel,the diameter of bubble,single bubble and double bubble on the number of adhesion removal and bubble wake entrainment were studied.The main results obtained are summarized as follows.(1)Adhesion removalThe adhesion number is increased with the increasing of inclusion diameter and inclusion number density,while inclusion density has little effect on it.The influence magnitude of inclusions properties on the adhesion removal are as follows:inclusion number density>inclusion diameter>inclusion density.The adhesion number is increased with the increasing of bubble diameter while leading to smaller adhesion number on unit bubble surface area.The adhesion number of two successive bubbles is more than the sum of those of two single bubbles.The surface tension,viscosity and density of the molten steel have little influence on adhesion removal of inclusions.(2)Bubble wake entrainmentThe inclusion entrainment number by bubble wake is increased with the increasing of inclusion number density and decreasing of inclusion daimeter,while inclusion density has little effect on it.Both the velocity distribution of the bubble wake and the floating height of the inclusions show a "high center and low sides" profile.Larger bubble diameter,greater wake velocity and size lead to lager entrainment number but smaller entrainment number in unit bubble volume.The wake velocity and size of double bubbles are larger than a single bubble,and the inclusion entrainment number is also more than the sum of those of two single bubbles.Inclusions can reach a higher position with the wake of two successive bubbles than with that of a single bubble.The surface tension,viscosity and density of the molten steel have no influence on the entrainment removal of inclusions.