| In the current study,the transport phenomena such as he multiphase fluid flow,mixing,behavior of bubbles and decarburization of the molten steel during RH vacuum process were investigated through water modeling,mathematical modeling and industrial trials.Firstly,the fluid flow and mixing phenomena during RH refining process were investigated using physical water modeling.The transient flow pattern on the vertical center plane of the vacuum chamber and ladle was measured using a Particle Image Velocimetry(PIV).The spatial distribution of the mixing time was measured through a DJ-800 multi-function monitoring system to monitor the electrical conductivity at specific points in the water model.The mixing time at the outlet region of the down-leg snorkel was the shortest.The measurement of the water modeling could be used to validate the numerical simulation.The relationship between the mixing time and the stirring power was:?m=27.04?-0.44(?m:s;?w:W/t).The relationship between the mixing time and the circulating flow was:?m,=-0.45Q+107.7(?m:s;W:kg/min).The motion and spatial distribution of bubbles,and the surface fluctuation in the vacuum chamber of the RH water model were investigated using a high-speed camera.The larger gas flow rate at the up-leg snorkel gave the larger maximum size of bubble,as well as the number of bubbles and the average gas volume fraction,while the average size of bubbles slightly increased.For bubbles,with the increase of the size,the number first decreased,then increased,and finally showed a decreasing trend.Secondly,the molten steel and argon two-phase fluid flow phenomena during RH refining process was numerically studied and analyzed including the multiphase fluid flow,the motion of bubbles,the recirculation and the mixing phenomena of the molten steel.A mathematical model of alloy melting was established,and two melting mechanisms were compared by considering whether an unmelted core of the alloy existed after the steel shell outside was melted.The aluminum alloy particles with a<5 cm size were completely melted after the steel shell outside the particle was melted,so that directly dissolved into the molten steel,which was defined as the first melting mechanism.Two mechanisms coexisted for the melting process of 70%Ti-Fe alloy particles with a 1 cm diameter.If the 70%Ti-Fe alloy particle was larger than 3 cm,the particle had a solid core after the steel shell outside was melted,which was defined as the second melting mechanism.Hence,both of two melting mechanisms should be considered for the melting of alloy particles with higher melting temperature and larger size.The alloy solute was gradually mixed in the molten steel after 3-4 cycles of the recirculation of the molten steel during RH refining process,approximately 200 s.The smaller the size of alloy particles was,the shorter the mixing time was.Thirdly,a mathematical model for the decarburization in RH refining process was established,coupling with the fluid flow.The decarburization reaction at three sites was considered,including the surface of injection lifting gas bubbles,the gas-liquid interface in the vacuum chamber and the interior of the molten steel bath.The effect of the flow pattern on the transfer of carbon and oxygen in the molten steel were obtained.The transfer of oxygen injected onto the top surface of the molten steel in the vacuum chamber was considered.The decarburization inside the molten steel bath in the vacuum chamber contributed the most,accounting for 55.9%of the total decarburization.The gas-liquid interface in the vacuum chamber and the surface of bubbles injected from the up-leg snorkel contributed approximately 32.5%and 11.6%,respectively.The decarburization rate of each region decreased gradually with the decrease of the carbon content in the molten steel.The oxygen blowing through the top of the vacuum chamber promoted the decarburization of RH refining whenever the oxygen was injected.When the oxygen was injected at the beginning of the decarburization,the contribution of the decarburization at the top surface of the molten steel in the vacuum chamber to the total decarburization increased from 11.6%to 28.3%.Mathematical models mentioned above were applied to the design and the optimization of the snorkel of the RH refining process,and industrial trials were performed.The oval shape down-leg snorkel enhanced the stirring effect in the vacuum chamber,and lowered the shear stress on the inner wall of the ladle,reducing the erosion of the lining refractory.Compared to the traditional circular snorkel,the circulating flow rate of the molten steel was increased by 15%,and the wall shear stress on the bottom and side walls of the ladle was reduced by 37.9%and 32.3%.The circulation rate of the molten steel using two oval snorkels was the largest and increased by 57%.The utilization of oval snorkels improved the decarburization efficiency of RH refining process,and the time to achieve<10 ppm carbon in the molten steel was reduced by about 90 s.Finally,the large eddy simulation(LES)was used to model the transient fluid flow and the decarburization of the molten steel of RH refining process.Firstly,the effect of the mesh refinement on the accuracy of the LES simulation was studied for the fluid flow in the water modeling of RH reefing process.As the mesh became finer,the calculation was more accurate.Compared to the k-? two-equation model,the LES could obtain the instantaneous velocity of the molten steel and many small vortices were constantly generated and dissipated in the molten steel during the circulation between the ladle and the vacuum chamber.The periodicity of the flow in the RH refining process could be analyzed using the LES.The fluid flow variables calculated by the LES model,such as pressure,velocity,turbulent kinetic energy and its dissipation rate,gas fraction within 13 s were stored during the calculation and were added to the decarburization calculation,and the fluid flow data was read every 1 s,so that the decarburization simulation by LES became feasible in the view of calculation time. |
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