Simulation Study Of Nozzle Clogging On Fluid Flow And Slag Entrainment In Continuous Casting Mold

Clogging of the submerged entry nozzle is a common problem during the continuous casting of aluminum-killed steel.The formation of clogging includes the adhesion,sintering and aggregation of inclusions on the nozzle wall.This process will change the flow pattern of steel within nozzle and mold,and the influence on the steel-slag interface is continuously deteriorated.In this paper,numerical and physical models were built to investigate the influence of nozzle clogging on flow field and slag entrainment in mold.The study of slag entrainment on steel-slag interface with nozzle clogging can provide theoretical guidance to reduce the defects caused by slag entrainment.First,a 0.25-scale water model,combined with Particle Image Velocimetry(PIV),was used to study the effect of nozzle exit shapes(rectangular and approximately oval)on flow field,characteristics of velocity near the liquid level and frequency of slag entrainment.A Large Eddy Simulation(LES)was conducted to investigate the characteristic of stream in nozzle exits.Main results show that the frequency of slag entrainment was higher for rectangular nozzle than that for approximately oval nozzle,though the flow speed of two nozzles were almost equivalent.The reason of this phenomenon was related to the effect of change rate of vorticity on slag entrainment.It was found that when slag entrainment occurred,the change rate in vorticity was often at the peak,i.e.,a point at which vorticity changed most rapidly.The mean value of vorticity in rectangular nozzle was larger than that in approximately oval nozzle,but there was no appreciable difference in change rates.In addition,the ratio of low-speed zone(velocity magnitude below 0.2 m/s)in rectangular nozzle was larger than that in approximately oval nozzle,inclusions were more likely to deposit in this zone to form clogging.Then,a three-dimensional model of nozzle clogging was built.DES model was used to calculate turbulent flow field,DPM model was used to track the movtion of inclusion particles and porous model was used to represent the effect of particle depositions on flow field.The results show that inclusions tended to accumulate and adhere to the bottom of nozzle and the lower side of the exits.The flow field in the nozzle changed as the clogging grew.With the growth of clogging,the average velocity at the nozzle exits decreased,while the velocity at the nozzle center and the maximum velocity at the nozzle exits increased gradually.In addition,particles with larger diameter were more likely to adhere to the wall surface and the deposition number of particle increased when the clogging grew over one certain thickness.Nozzles with clogging ratio of 0%,10%,30% and 50% were made to study the influence of nozzle clogging on the flow field and slag entrainment.The flow in mold using normal nozzle was symmetrical double-roll pattern,while the flow was asymmetric with clogging nozzle.From the liquid level shape and oil thickness,the liquid level with nozzle clogging was not stable,and the upper roll flow was enhanced.When the ratio of nozzle clogging was less than 10%,the frequency of slag entrainment was small.While the ratio of nozzle clogging increased to 30% and 50%,the frequency of slag entrainment increased obviously,and this trend was more pronounced with the increase of casting speed and the decrease of the viscosity of oil.Moreover,the average speed near the oil-water interface at 1/4 mold width were larger using clogging nozzles than that using no-clogging nozzle,the shear force increased and the oil droplets were more likely to be dragged into mold to form slag entrainment.