Degree Name

Doctor of Philosophy


Department of Materials Engineering


The present project was conceived as a fundamental study of the interaction between oxygen jet and liquid metal bath and the effect of bottom blowing on the interaction in the combined blowing BOF steelmaking processes with respect to droplet generation due to the jet impingement, the droplet size distribution and the droplet residence time.

Mechanisms of droplet generation and mechanisms of the effect of bottom blowing on droplet generation were investigated in a 2-D water model, using high speed cinephotography. Two mechanisms of the droplet generation, "dropping" and "swanning", were found, corresponding to low and high jet gas flow rates respectively. Ejection of individual droplets and liquid fragments are characteristics of the "dropping" and the "swarming" regions respectively. It was found that the significant increase in the droplet production due to bottom blowing is principally caused by the interaction between the top and bottom blowing in the impingement zone, and not by the bottom blowing as such.

The droplet production, droplet size distribution and droplet residence time were experimentally studied in a wide range of blowing parameters such as gas flow rates through top lance and bottom tuyeres, lance height and bottom tuyere location etc., using 2-D and 3-D water modelling and 3-D mercury/glycerine modelling. The relationship between those three phenomena and the blowing conditions were established. The evidence obtained from this study suggests that there is a strong indication to take the momentum number as a link between the model and the prototype in terms of droplet generation due to an impinging gas jet.

All findings from this study can be explained based on the "ripple theory" of the generation recommended from this work.