Study On Multiphase Flow And Mixing During Grade Change Process Of A Five-strand Bloom Tundish

In the process of continuous casting of different steel grades,it is inevitable to produce intermixing slab,which needs to be downgraded only even treated as scrap steel,resulting in a certain loss of molten steel.Therefore,it is the pursuit of low cost clean steel production to reduce the length of the intermixing slab on the premise of ensuring the quality of the intermixing slab and smooth production.In this study,a mathematical model coupled turbulent flow,multiphase flow with species transport model was firstly developed to investigate the behaviors of steel-slag-air interfaces and the steel mixing in a five-strand bloom casting tundish under different emptying time and refilling modes.And water model experiments were conducted to verify the coupled model.Subsequently,the effect of flow control devices?FCDs?on the steel mixing behavior during the grade change process were studied based on the research outcomes of the flow field in the tundish at steady-state casting under different FCDs.a mathematical model was established to study the influence of the structure of the flow control device on the flow field of tundish during steady pouring.The results are showed as follows:?1?When the ET increases from 3 to 4 min,the mixing times at the 3^rd,4^th and 5^thh strands where the concentrations of new grade reach to 90%are reduced by 174?187and 53 s,respectively.The steel exposure trends tend to be stable when the refilling time is over 60 s,and the exposed areas are remained at 50 cm²?84 cm² and 124 cm²when the emptying times are 2 min?3 min and 4 min,respectively,which are far less than the value of 310 cm² when the ET is 5 min.The proper emptying time should be4 min based on the multiphase flow and steel mixing behaviors.?2?When the filling rate remains equal to the injection rate at steady-state casting period at the beginning of refilling process after the tundish is emptied by 4 min,there only exist one stage of molten steel exposure,which ends at 3 s and the duration time of steel exposure is shorter compared to other refilling modes.In the process of continuous casting of different steel grades,the mixing time of molten steel increases with the rise of the stable pouring level during mixed casting,while the dead zone volume decreases with the rise of the stable pouring level.?3?During the steady-state casting,the baffle has a significant influence on the flow state of molten steel,while the dam and turbulence inhibitor have relatively small effect on the molten flow in the tundish.When the tundish is equipped with baffle?Case A2?,the mean residence time is decreased by 100.3 s,the overall mean standard deviation of each flow concentration decreased by nearly 46%,the volume of piston region decreased by 13.5%,and the dead zone was decreased by 6.4%,compared to Case A2?without baffle?,respectively.Moreover,the average residence time and the flow consistency among strand can be obviously decreased.?4?For the grade change process under different FCDs,the baffle has a great influence on the steel mixing in tundish,while the dam and turbulence inhibitor have less effect on the steel mixing behavior.Compared with A1,the mass fraction of new grade reaches 90%at 333 s near the 3^rd strand,and the mass fraction of new grade at the 5^thh stand remains around 80%at the later stage,which can seriously deteriorate the steel mixing and the consistency among strands.