Modeling Of Motion And Interaction Of Discrete Phases In Continuous Casting Mold

In the process of molten steel flow from the tudish into the mold through a nozzle,the inclusions such as Al2O3,SiO2 easily gathered on the nozzle wall.It can cause the nozzle clogging and make great harm to slab quality.In order to prevent the nozzle clogging,the technology of argon blowing was introduced into the nozzle.The argon bubble injection plays an important role in affecting the floatation,removal of inclusions,enhancing the temperature and composition of liquid steel.However,improper control of the argon bubble injection may bring negative effects.On the one hand,some too large bubbles float up to the mold top surface and break up,which will induce turbulence and lead to mold powder entrapment forming slab surface defects.On the other hand,some small bubbles may be trapped forming "pencil pipe" defects if they couldn't rise to top surface in time.In consequence,study on the motion behavior of discrete phase in the continuous casting mold and the mechanism of inclusion removal by bubble is particularly important to promote the quality of steel products.In this work,based on the process of argon bubble blowing in continuous casting mold as the research object,the motion and interaction of discrete phase in the continuous casting mold were studied by both physical experiment and mathematical simulation.The main contents are as following:Based on the similarity theory,a water model of argon blowing mold was established to record the motion process of bubbles using a high speed camera system.The images of bubbles motion were analyzed by an image processing software to obtain various parameters describing the bubble behavior.The results show that the bubble average size decreased from the nozzle exit to the narrow wall of mold.The water flow rate has the greatest influence on the bubble number density distribution,while the gas volume rate has very significant influence on the bubble size.The increase of SEN(submerged entry nozzle)immersion depth makes the bubbles distribution range more homogeneous.The experimental results show that,the shape of small bubble is spherical,and with the increase of bubble size,the shape was deformed to ellipsoid.The bubble rising velocity was studied and the experimental results are consistent with formula fitting curve.The inclusion removal mechanisms include not only the adhesion removal but also the bubble wake flow entrainment.The interactions of bubbles and bubble with solid particles were analyzed based on the experimental results,which provides the basis to establish the model of discrete phase interaction.The Eulerian-Lagrangian method was used to establish the gas-liquid two phase mathematical model in the continuous casting mold,and the interaction between bubbles was considered in the model.Using the new mathematical model,the movement of gas-liquid two phases was simulated and the model was validated from two aspects:fluid and bubble motion behaviors.The simulation results show that,the velocity of jet zone changed markedly under the condition of argon gas blowing.With the argon gas blowing,the bubble buoyancy force raised the jet zone and decreased the downward inclination angle of jet flow,which plays an important role in weakening the jet.In addition,the phenomenon of bubbles interaction was observaed in both physical experiment and simulation results,which proves that considering the interaction of bubbes is necessary and feasible.Using the mathematical model with bubbles interaction,the distribution rule of bubble size,quantity and volume fraction was discussed under different conditions.The simulation results show that the behavior of bubbles gathering in the nozzle and break up out the nozzle exit.The influence of bubble blowing on the inclusions removal also was also studied.A mathematical model coupled the volume of fluid method(VOF)and discrete particle method(DPM)was developed to study the behavior of inclusions adhesion removal and wake flow entrainment.The effects of inclusion size and quantity,bubbtle size,single bubble and succeeding bubble pair on inclusion removal were studied.The simulation results show that,with the size of inclusion increasing,the number of adhesion removal increased,but the number of wake flow entrainment decreased.The increase of inclusion number density lead to the increase of adhesion removal and wake flow entrainment.On the other hand,with the bubble size increasing,the inclusion number of adhesion removal and wake flow entrainment increased,but the number of adhesion and entrainment of unit surface area and volume of bubble decreased.This results indicate that small bubbles have better removal efficiency than large bubbles.During the ascending process of a succeeding bubble pair in the molten steel,their inclusion removal by adhesion and entrainment are more than the sum of two single bubbles,which shows that the contribution of succeeding bubbles on inclusions removal is of great significance.