Mixing time, as a key parameter for evaluating ladle refining efficiency, has long attracted extensive attention from researchers. In typical experimental studies, salt solution tracers are introduced into ladle water models to assess the degree of mixing within the ladle. Previous studies have demonstrated that the volume of tracer can significantly influence the measured mixing time. However, the gas flow rates employed in these studies are generally relatively high, whereas, in industrial operations, especially during final composition adjustments, lower gas flow rates are often applied. To systematically investigate the effect of the salt solution tracer volume on the mixing efficiency in a ladle water model under asymmetrical gas stirring with a low gas flow rate, a 1:3-scaled water model was developed based on a 130-ton industrial ladle. The mixing behaviors corresponding to different tracer volumes were comprehensively analyzed. The results indicate that the relationship between tracer volume and mixing time is non-monotonic. As the tracer volume increases, the mixing time first decreases and then increases, reaching a minimum at 185 mL. When the tracer volume was small, the dimensionless concentration curves at Monitoring Point 4 exhibited two distinct patterns: A parabolic profile, which was when the tracer initially moved through the left and central regions and then slowly crossed the gas plume to reach the monitoring point. A sinusoidal profile, which was when the tracer predominantly circulated along the right side of the ladle. When the tracer volume exceeded 277 mL, the concentration curves at Monitoring Point 4 consistently exhibited a sinusoidal pattern. Compared with moderate gas flow conditions (8.3 L/min), the peak concentration at Monitoring Point 3 was significantly lower under a low gas flow (2.3 L/min), and the overall mixing time was longer, indicating reduced mixing efficiency. Based on the findings, a recommended tracer volume range of 185–277 mL is proposed for low gas flow conditions (2.3 L/min) to achieve accurate and efficient mixing time measurements with minimal disturbance to the flow field. It was also observed that when the tracer concentration was relatively low, the mixing behavior throughout the ladle became more uniform.

A novel right-sidewall gas blowing method is proposed to improve the flow behavior in a single-strand tundish. Despite advances in tundish flow control, the impact of slag layers and sidewall gas injection on flow dynamics and tracer transport remains underexplored. This study combines 1:3.57 scale water model experiments and Compuational Fluid Dynamics (CFD) simulations to investigate the effects of gas injection heights (50 mm and 100 mm) on flow structure, mixing efficiency, and slag layer interactions. Particle Image Velocimetry (PIV) and the stimulus-response method are used for quantitative validation. Results show that sidewall gas blowing suppresses short-circuit flow, increases average residence time by up to 37%, and reduces dead zone volume by up to 19%. The 50 mm blowing height induces stronger surface turbulence, while the 100 mm height improves flow uniformity. The presence of a slag layer significantly dampens surface fluctuations and alters vortex formation. These findings fill a critical research gap in tundish metallurgy and offer a practical reference for optimizing gas blowing strategies in industrial applications.

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.