The Study Of The Bubble Formation Mechanism And The Motion Behavior In Liquid Steel

The bubbling in liquid steel can improve steel cleanliness effectively.To understand the single bubble behavior and the interactions between two bubbles,which are basis to analyze the mechanism of gas-liquid two-phase flow in metallurgical vessel.Hence,the bubbling has been systematically studied by both water-model experiment and three-dimensional numerical simulation.Firstly,the paper calculated the bubble diameter by the two stage model using MATLAB.The size of physical model is designed by the calculated bubble diameter.The influences of gas flow rate,orifice diameter and surface tension on bubble size were preliminary analyzed.Using a high-speed camera,a water-model experiment is built.The images of air bubbles emerging from the nozzle diameters of 1.5,2,and 2.5 mm were investigated within a certain range of gas flow rate by the water-model experiment.The volume of fluid(VOF)model in conjunction with continuum surface force(CSF)model was used to describe the interface between the gas and liquid on the software platform of Fluent 14.5.The simulations were validated with the water modeling results.Finally,a mathematical mode of bubble formation and motion in liquid steel is built,and the bubble formation,rising motion,shape change,coaxial bubbles coalescence and parallel bubbles bounce have been systematically studied by this model in argon-steel system.The results show that the initial bubble sizes increase with increasing gas flow rate or nozzle size,whereas is relatively independent of the nozzle size when gas flow rate is 0.975 L/min.There is a constant bubble volume and a constant bubble frequency when the gas flow rate is 0.175 L/min and 0.675 L/min for nozzles of 1.5,2and 2.5 mm,and the bubbling regimes are 0.975,1.025 and 1.325 L/min.The terminal velocities of all bubbles are around 0.32 m/s.The trajectory of 3D rising bubbles with the size of 7.82-10 mm is a spiral way with strong instabilities by changing their instantaneous shapes in the liquid steel,while 10-15 mm bubbles rise rectilinearly.The evolution history of bubble shape changes from non-deformed(spherical)to the deformed shapes(spherical cap,ellipsoidal,wobbly or ellipsoidal cap)without coalescence.Calculated velocity and pressure distributions indicated that the rising velocity of the trailing bubble is larger than that of the leading bubble,which result in two coaxial bubbles coalescence.The small eddies on the inner edge of two parallel bubbles eventually lead to bubbles bounced each other.