Simulation Of Two-phase Flow Behavior Of Jet Impinging On Molten Pool Under Low Vacuum

With the increasing market demand for ultra-low carbon clean steel,RH oxygen blowing technology developed rapidly.RH oxygen blowing refining has become the core technology of producing high quality ultra-low clean steel.Due to the lack of basic theoretical research on jet impinging on high-temperature melt under vacuum,most of the oxygen nozzles and related processes for RH vacuum are dependent on imports.Therefore,the study on the two-phase flow of supersonic oxygen jet impinging on molten steel under vacuum will reveal the gas-liquid interface phenomenon during the impinging process and provide a theoretical basis for the understanding of the actual process on site,which will be helpful for the localization of RH oxygen equipment and technology.Based on the in-depth analysis of the characteristics of gas-liquid two-phase flow,this paper constructs a simulation algorithm that can describe the high-density differential two-phase flow.Based on the VOF two-phase flow model,this paper analyzes the interface instability caused by the supersonic oxygen jet impinging on the steel surface and its surface deformation,splashing and droplet behavior.This paper also discusses the shape of pits,the internal flow of weld pool and spillage amount when oxygen jet impinges on molten pool at different Mach Numbers,so as to reveal the law of oxygen jet impinged on molten body in vacuum state.The discussion not only provide theoretical basis for determining the structure size of RH oxygen nozzle but also formulate the spraying process,so as to realize the efficient and safe production of RH.The main conclusions are as follows:(1)Because the supersonic gas jet impinges on molten steel in vacuum state is a high temperature and complex multiphase reaction,it is extremely difficult to adopt the simulation algorithm of direct coupling.The algorithm is improved in this paper,and the regional simulation method is adopted.The feasibility of the simulation method is verified by comparing the experimental results in the literature with the simulation results in this paper.(2)The Kelvin-Helmholtz instability arises from the instability between two different fluid interfaces with velocity differences.Jet impingement process is a typical gas-liquid two-phase flow process with large velocity gradient and large density difference.When the impact force is large,the surface wave is generated on the gas-liquid interface.When the shear stress on the interface is greater than thesurface tension of the liquid,the surface wave is destroyed to form droplets.At the same time,most of the droplets were splashed from both sides of the impact crater.(3)The blowing number is a dimensionless quantity integrating Reynolds number and Prandtl number,which reflects the relationship between inertia force,viscous force and surface tension.And it is used to judge the critical condition of spillage.In this paper,the field RH furnace is taken as the research object to simulate the blowing number under different ambient temperature and nozzle position conditions.The blowing number is the function of the ambient temperature and nozzle position.When the temperature is constant,the blowing number decreases with the increase of nozzle position.When the nozzle position is 30 de,the ambient temperature increases from 298 K to 1873 K,and the blowing number increases by 3 times,in this paper,the average blowing number is 17.(4)In this paper,the shape of impact crater and the splash intensity of oxygen jet at different Mach number are simulated under the same nozzle position.Through nonlinear fitting of simulation results,the empirical formulas of impact crater depth and diameter under different Mach Numbers are obtained.It is concluded that with the increase of Mach number,the crater depth increases,the crater diameter decreases and the splash strength increases,When the Mach number increases from2.5 to 3.5,the impact crater depth increases by 0.5 times and the impact crater diameter decreases by 0.4 times.Under the same Mach number,the simulation analysis of the variable operating conditions is carried out.The surface deformation,spillage behavior and flow law of molten pool at 30 de,35de and 40 de are described.Under the same nozzle position,the behavior of gas-liquid interface is discussed when the environmental pressure is 8000 Pa,7000 Pa and 6000 Pa respectively.It is concluded that the stagnation pressure,nozzle position and vacuum degree are the main factors that affect the shape of impact crater and the flow process of molten steel.And the nozzle position is the most important factor.