Per: pedro francelino garcia (Instituto federal do espírito santo), lucas martins basilio (INSTITUTO FEDERAL DO ESPÍRITO SANTO), Ayrton Cavallini Zotelle (INSTITUTO FEDERAL DO ESPÍRITO SANTO), breno totti maia (lumar metalúrgica ltda), josé roberto de oliveira (INSTITUTO FEDERAL DO ESPÍRITO SANTO), renato do nascimento siqueira (instituto federal espirito santo), joão paulo barbosa (instituto federal do espírito santo)
Abstract:
Convergent-divergent nozzles are widely used in Basic Oxygen Furnaces (BOF) to accelerate oxygen to supersonic speeds, allowing the process of decarburization of the hot metal. Different flow conditions, including overexpanded, underexpanded, and near ideal flows, exhibit distinct flow characteristics. The complex structure of the flow inside supersonic nozzles in the startup process includes shock waves, recirculation zones and expansion waves, factors that will affect the efficiency of the hot metal mixing process, due to the change of the potential core size. In this study, ANSYS Fluent® 2022 software was used for a 2D axisymmetric simulation of a trapezoidal converging-diverging nozzle similar to that used by ArcelorMittal Tubarão. The SST k-ω turbulence model was employed, and the analysis was performed in the transient regime. Schlieren pictures were used to analyze the phenomena that occurred in the startup of the supersonic jets. The results indicate that high nozzle pressure ratios (NPR) lead to high density gradients at the beginning of the flow in the nozzle, with the presence of incident shocks, contact discontinuity, and vortices. For low NPR values, early separation of the jet boundary layer is observed, causing a backflow that allows ambient air to enter the nozzle, reducing its lifespan. The size of the potential core also varies with NPR, and nozzles with higher pressure ratios present larger potential cores, which contributes to generating the turbulence required to induce steel refining reactions.
