A Physical Model Study of Two-Phase Gas–Liquid Flows in a Ladle Shroud

Abstract

Argon-steel flows inside a ladle shroud during teeming from a ladle to a tundish have been modelled physically. To this end, full-scale Perspex models of bloom as well as slab casting shrouds (BCS and SCS), operating with air and water, have been applied. Both open to air as well as immersed conditions were investigated with and without gas injection. Flows inside a ladle shroud under open to air and immersed conditions were found to be substantially different with a strong function of gas and liquid flow rates, collector nozzle and shroud diameters. Depending on the volumetric gas injection rate relative to liquid flow rate, different flow regimes have been observed in an immersed shroud $$ \left[ {i.e.,\,\,0 < \left( {\frac{{d_{\text{s}} }}{{L_{\text{s}} }}} \right) \le 0.24} \right]. $$ At extremely low gas flow rates, $$ \left[ {i.e.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right) \le 0.02} \right], $$ injected gas is completely entrained as bubbles by the down-flowing liquid resulting in a bubbly two-phase flow over the entire length of a shroud. However, with an increasing gas flow rate, two distinctly different regions start to develop within the shroud body: a free liquid jet in the upper part and a gas–liquid mixing zone below. The length of the free jet increases with an increasing gas flow rate and at significantly higher gas to liquid flow rates $$ \left[ {viz.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right)_{\text{BCS}} \ge 0.42} \right] $$ and $$ \left[ {viz.,\,\,\left( {\frac{{Q_{\text{g}} }}{{Q_{\text{L}} }}} \right)_{\text{SCS}} \ge 0.30} \right] $$ , and the free jet is found to prevail over the entire length of the shroud. Within the range of conditions studied, it is observed that the free jet length or the line of demarcation between the jetting and two-phase mixing zone depends on gas and liquid flow rates and is specific to a particular shroud-collector nozzle system. Physical model results further indicate that a sufficiently large free jet length (~ shroud length) tends to create a high pressure region inside a shroud and prevent ingression of air. Possible implications of the present findings with reference to industrial teeming practices are also discussed in the text.