AbstractMathematical and water models were used to study the flow behaviour of the gas bubbles and the molten steel in gas stirred ladles with and without an immersion hood. The mathematical model is based on a computatioal fluid dynamics technique which can handle the interactive, two phase (gas–liquid) flow problems and which allows the top surface of the melt to fluctuate. The water model is 1/10 scale of a 150 ton steel ladle. Water, a plexiglass container, and helium gas substitute for molten steel, the refractory ladle, and argon gas, respectively, in the actual steel ladle. The mathematical model developed was first tested under the same conditions used in the water model. Results of the analyses, including bubble pathlines and melt flow patterns, showed very good consistency with observations from the water model. The mathematical model was then used to study the phenomena in the steel ladle operations. The results showed that the flow behaviour in the steel ladle was very similar to that in the water model. However, the flow patterns of the molten steel with and without the addition of an immersion hood were considerably different. It was shown that the immersion hood not only can provide slag free surface and protective atmosphere inside the hood, for which it was originally designed, but also can produce a more favourable flow pattern for the molten steel in the ladle.MST/1031