1. Introduction

Removal of impurities and nonmetallic inclusions contained in molten metals is of essential importance for producing high-quality metal products. Such an operation is called refining. The refining can be effectively achieved by enhancing the opportunity for the impurities and nonmetallic inclusions to meet their respective refining agents carried into the reactor. Such requirement is satisfied when the bath of the reactor is strongly mixed. Mixing of the bath is usually done by injecting gas into the bath. A molten metal flow is induced in the bath through the gas-lift effect, and the flow contributes to the bath mixing. Consequently, information on the flow field in the bath is necessary for enhancing the efficiency of the conventional metal refining processes as well as for developing novel processes. Molten metals contained in the reactor of the real refining processes are not transparent, and their temperature is very high. In addition, the molten metal flows in the real refining processes are highly turbulent and unsteady in many cases. A full understanding of the real molten metal flows therefore is not easy. Cold model experiments are often chosen for investigating the molten metal flows. Flow visualization techniques are suitable for whole flow field measurements. In this chapter, an outline of the flow field in the bath of real materials processes at high temperatures is briefly introduced.