Influence of Turbulent Flows in the Nozzle on Melt Flow Within a Slab Mold and Stability of the Metal–Flux Interface ISMAEL CALDERON-RAMOS and R.D. MORALES The design of the ports of a casting nozzle has profound effects on the fluid flow patterns in slab molds. The influence of these outlets have also considerable effects on the turbulent flow and turbulence variables inside the nozzle itself. To understand the effects of nozzle design, three approaches were employed: a theoretical analysis based on the turbulent viscosity hypothesis, dimensional analysis (both analyses aided by computer fluid dynamics), and experiments using particle image velocimetry. The first approach yields a linear relation between calculated magnitudes of scalar fields of e (dissipation rate of kinetic energy) and k 2 (square of the turbulent kinetic energy), which is derived from the wall and the logarithmic-wall laws in the boundary layers. The smaller the slope of this linear relation is, the better the performance of a given nozzle is for maintaining the stability of the melt–flux interface. The second approach yields also a linear relation between flow rate of liquid metal and the cubic root of the dissipation rate of kinetic energy. In this case, the larger the slope of the linear relation is, the better the performance of a given nozzle is for maintaining the stability of the melt–flux interface. Finally, PIV measurements in a mold water model, together with equations for estimation of critical melt velocities for slag entrainment, were used to quantify the effects of nozzle design on the dynamics of the metal–slag interface. The three approaches agree in the characterization of turbulent flows in continuous casting molds using different nozzles. DOI: 10.1007/s11663-015-0569-6 Ó The Minerals, Metals & Materials Society and ASM International 2016 I. INTRODUCTION MOLD flux, or mold slag entrainment, is character- ized by flux being drawn into the bulk of the steel melt. Mold flux entrainment causes surface and internal defects in the slab and in the final product. The solidifying steel shell can trap particles of slag entrained by the liquid turbulence in the mold interacting with the flux, affecting steel cleanliness. This aspect has been the subject of much attention by steelmakers over several years due to the large amount of downgraded, condi- tioned, or even rejected slabs that hinder caster produc- tivity and business profits. Essentially, melt flow dynamics in the mold and at the melt–flux interface, as well as the physical properties of both phases, govern flux entrainment, along with heat and mass transfer among other process variables. This is the reason behind the interest of many researchers in studying fluid dynamics in the mold. Gupta and Lahiri studied, through scaled water models using nozzles with circular ports, surface disturbances in the mold. [1] These authors reported that the wave’s amplitudes, at the melt level, increase with fluid velocity through the ports of the nozzle. With the increase of the aspect ratio of the mold (W/T, where W is width and T is thickness), the amplitude decreases because the size of the upper recirculating zone becomes larger. In addition, there is a linear relationship between the dimensionless wave amplitude with the Froude number. Kalter et al. [2] using scaled molds and nozzles with square ports, found similar results (Figure 5 of their paper). With low-mold aspect ratios, meniscus fluctuates with frequencies in the gravity wave regime. He Qinglin et al. [3] worked with a full-scale model and reported on the influence of nozzle immersion depth on fluid flow. According to those authors, immersions as large as 217 mm have a small influence on fluid velocity at the meniscus level. When immersions are smaller than 52 mm, velocities in the bath surface decrease but the kinetic energy increases because the magnitudes of the fluctuating velocities become larger. Unfortunately, these authors did not report the geometries of the ports. Gupta and Lahiri [4] studied the influence of oil layers on the bath surface and found again a linear relationship between the ratio of the wave’s amplitude and the port diameter with a modified Froude number. Among the few works, considering the effects of nozzle ports geometries on fluid flow through their discharging areas, there is that of Najjar et al. [5] using CFD mathematical simulations. According to these authors, thick nozzle walls control ISMAEL CALDERON-RAMOS, Graduate Student, is with the Department of Metallurgy and Materials Engineering, The National Polytechnic Institute-ESIQIE, Col. Zacatenco, Mexico D.F., CP 07738, Mexico. R.D. MORALES, Professor, is with the Department of Metallurgy and Materials Engineering, The National Polytechnic Institute-ESIQIE, and President, K&E Technologies, Col. San Pedro Zacatenco, Mexico D.F. CP 0.7369. Contact e-mail: rmorales@ipn.mx Manuscript submitted September 8, 2015. Article published online March 31, 2016. 1866—VOLUME 47B, JUNE 2016 METALLURGICAL AND MATERIALS TRANSACTIONS B