Zhuoyue Du

Metallized pellets are spherical iron-bearing burden materials obtained by treating iron ore pellets through processes such as direct reduction. They contain a certain proportion of metallic iron and mainly consist of metallic iron, incompletely reduced oxides, gangue, and other nonmetallic components. They are one of the commonly used iron-bearing materials in electric smelting furnaces. The melting process of metallized pellets not only affects the melting efficiency of the charge but is also accompanied by slag–metal separation and gangue separation, which is directly related to mass transfer, heat transfer, and production efficiency during the smelting process. However, existing studies have mainly focused on the melting behavior of pellets in a single-phase molten pool, while studies on gangue separation, interfacial migration, and slag–metal separation during pellet melting at the slag–metal two-phase interface remain rare. Because this region involves complex interfacial heat transfer, fluid flow, and interfacial interactions, investigating only the overall melting process of pellets is insufficient to reveal the actual gangue separation mechanism. Therefore, a systematic investigation of the melting and separation processes of pellets at the slag–metal interface is necessary. Based on the principle of similarity, a water–oil–ice three-phase physical model was employed in this study, in which water, silicone oil, and ice balls containing dyed silicone oil samples were used to simulate molten iron, slag, and pellets, respectively. The dyed silicone oil is specially designed to simulate the gangue in the pellet. Visualization experiments were conducted to investigate the evolution of pellet melting morphology, oil droplet (gangue) release behavior, and diffusion characteristics in the oil layer under different initial oil droplet positions and static or parallel flow conditions. The results show that the initial position of the oil droplet and the parallel flow significantly affect the local melting behavior of the ice ball and the oil droplet release process. In particular, the release time of the oil droplet located above the ice ball is significantly longer than that of the oil droplet located below the ice ball. The parallel flow significantly changes the melting sequence of the ice ball and the oil droplet release path by enhancing convective heat transfer in the lower region of the ice ball. According to the initial position of the oil droplet and the flow conditions, the oil droplet release process can be classified into five typical separation types, including (1) lateral release of the upper oil droplet after the ice shells on both sides melt through, (2) release of the upper oil droplet through a hole at the bottom of the upper hemisphere, (3) direct release of the lower oil droplet through a local hole, (4) two-stage release of the lower oil droplet controlled by interfacial constraint, and (5) single-stage release of the oil droplet on the downstream flow side driven by parallel flow. The oil droplet release time in the parallel flow cases is shorter than that in the static conditions. The diffusion behavior of the oil droplet after entering the oil layer is weakly affected by the parallel flow and is mainly characterized by inertial diffusion along the initial release direction, followed by spreading toward the surrounding area. This study reveals the slag–metal separation mechanism during pellet melting at the slag–metal interface under the combined control of flow, ice shell morphology, and interfacial interactions, providing experimental evidence for optimizing the melting and separation behavior of pellet charges in electric smelting furnaces and related smelting processes.

During continuous casting, the flow behavior of liquid steel in the tundish directly affects the temperature distribution of liquid steel, inclusion removal, and billet quality. In tundish-related research, water model experiments remain an intuitive method for investigating the flow process in the tundish. However, water model experiments are often conducted in different seasons, and variations in experimental temperature can change fluid properties such as density and viscosity, thereby affecting flow characteristics and the comparability of experimental results. In this study, a 1:3.57 transparent bare single-strand tundish model made of acrylic was used, and the differences in tracer transport processes at 7 °C and 20 °C, as well as the influence of different tracer dosages on the experimental results, were systematically investigated through flow visualization and stimulus-response experiments. The results showed that, under the 7 °C condition, the upward transport tendency of the pure ink tracer was weakened, the overall flow remained closer to the tundish bottom, the transport speed decreased, and the time required to reach the outlet was significantly prolonged. For the saturated KCl solution tracer, a lower temperature enhanced its transport along the bottom toward the outlet and suppressed its diffusion toward the liquid surface. The RTD results showed that, after the temperature was increased, the curves shifted to the left as a whole, and both the peak time and the mean residence time were shortened. The outflow percentage of tracer results showed that the difference for the 10 mL saturated KCl solution between the 7 °C and 20 °C conditions was the most significant. At 7 °C, the total outflow percentage of the 10 mL salt solution tracer at 1500 s was 76.86%, which was 22.97% lower than that at 20 °C. As the tracer dosage increased, the differences in the transport process, RTD curves, and outflow percentage curves under different temperature conditions gradually decreased, indicating that the effect of dosage on the experimental results gradually became stronger than that of temperature. These results indicate that the combined effects of experimental temperature and tracer dosage cannot be neglected in tundish water model experiments.

Secondary refining is a critical stage that determines steel properties. Its effectiveness is directly governed by the flow and mixing behavior of molten steel. At present, water model experiments are widely employed to investigate flow and mixing behavior during ladle refining. However, the effects of tracer volume and the geometric scale ratio are often neglected. In this study, a 130 t industrial ladle was taken as the prototype, and two water models with geometric scale ratios of 1:5.6 and 1:3 were established. Six tracer volumes were designed to systematically investigate the flow and mixing behavior under different geometric scale ratios. The results show that, with increasing tracer volume, the transport pattern in the small ladle transitions from a top-to-bottom to a center-to-side, whereas in the large ladle, the transport pattern consistently remains top-to-bottom. In both ladles, the mixing time at all monitoring points exhibited a trend of first decreasing and then increasing with increasing tracer volume, although the inflection points differed between the two ladles. For the small ladle, the turning point occurred at Dimensionless tracer amount (Dta) = 0.39 × 10⁻³, whereas for the large ladle, it occurred at Dta = 0.26 × 10⁻³. Further analysis indicates that when Dta > 0.51 × 10⁻³, tracer injection in the small ladle significantly disturbs the original flow field structure. Therefore, the optimal tracer volume for the small ladle is Dta = 0.39 × 10⁻³. In contrast, the large ladle maintains a relatively stable flow field even at higher tracer volumes. This study clarifies the volume of tracers and the selection of geometric scale ratios. The research results can effectively reduce measurement errors and enhance the reliability of experimental results.

This study experimentally investigated, using a water-model hydrodynamic analogue, the effects of crystallizer rotational speed and baffle configuration on the flow-field structure, mass transfer, and mixing behavior inside the crucible of a rotational segregation model system relevant to silicon processing. Three configurations were examined: no baffle, straight baffles, and inclined baffles. Flow visualization and stimulus–response tracer experiments were conducted at 200 and 300 rpm to compare their effects on the main flow pattern and mixing characteristics. The results showed that, without baffles, a complete annular main flow formed, and the fluid moved downward spirally along the crystallizer wall. Mixing was relatively fast, indicating limited potential for local tracer retention. With straight baffles, the main flow was strongly obstructed and redistributed, and the mixing time in local bottom regions, especially in front of the 90° baffle, was markedly prolonged. This behavior suggested a more favorable hydrodynamic environment for local retention and accumulation in the model system, and the effect was most evident at 200 rpm. With inclined baffles, transport in the upper region was enhanced, whereas bottom flow was weakened. Although the tracer could move downward along the baffle surface, it was rapidly swept away after reaching the bottom, indicating reduced stability of local accumulation. Increasing the rotational speed from 200 to 300 rpm strengthened the overall flow and shortened the mixing time under all conditions. Overall, straight baffles, particularly at 200 rpm, produced the strongest tendency for local retention in the present model system. These results provide preliminary hydrodynamic insight into flow regulation and transport behavior in rotational segregation systems.