A Numerical Investigation on VOD Nozzle Jets

Detta är en avhandling från Stockholm : KTH Royal Institute of Technology

Sammanfattning: The metallurgic process, Vacuum Oxygen Decarburization (VOD) process, is used for producing stainless steels with ultra-low carbon grades. In a VOD process, an oxygen lance is equipped with a De Laval nozzle which injects high speed oxygen gas. The aim of this work is to increase the knowledge of the flow behavior in the harsh environment of VOD vessels. Two real VOD nozzles from industry were numerically studied and compared at different temperatures and ambient pressures. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on the jet velocity and the dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed an incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under-expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that a variation in the ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure.For the comparison between the two nozzles concerned, the modeling results showed that one of the nozzles was more applicably proper for lower pressures, displaying a more stable flow pattern. Furthermore, it was found that a change in ambient pressure has a stronger effect on the jet force than a change in ambient temperature. In addition, it was proved that the profiles of the dynamic pressure at a certain blowing distance fit well to Multi-Gaussian curves.