Analysis of waves in a cavity and their significance to splashing in steelmaking
Creators: name: Sabah, Shabnam
name: Brooks, Geoffrey
name: Naser, Jamal
Publisher: name: Swinburne
Year: 2024

description: In steelmaking, metal droplets are generated due to the impact of supersonic jets onto the liquid metal bath. This phenomenon is generally referred to 'splashing' [1]. Splashing is an important phenomenon as it provides large interfacial area between reacting phases and promotes high overall reaction rates. Dogan et al. [2] estimated that 60% of decarburization in steelmaking process takes place in the gas-metal-slag emulsion phase during the main blow. Therefore, it is important to understand droplet generation if we are to optimize steelmaking processes. In literature only a few works [3,4] discuss the formation of waves in the cavity. But there is lack of understanding how waves inside the cavity affect splashing. In the present work, a 1/10th cold model of oxygen steelmaking was used to study wave phenomenon in the cavity and how its characteristics vary with the changing momentum of impact jet and thereby affecting splashing. Compressed air was passed through a top straight nozzle. Water was used to simulate liquid steel. As the first phase of the investigation, the slag phase was not included in this study. A transparent cylindrical rig, made of perspex sheet was used as the vessel. A high speed camera (MotionPro Y, model Y4L (1024x1024 - 4000 fps)) was used to take photos of the cavity and the splashing at a rate of 30 frames/ second for a time duration of 4 minutes. In addition, a video of 2 second was taken at 2000 frames/ second rate in order to observe the droplet generation process. As air jet hit the water surface, it created waves inside the cavity. These waves were pushed towards the edge of the cavity by deflected gas flow. At the edge of the cavity, these waves grew to certain critical amplitudes. These waves were like sheets structure at the edge of cavity. They were similar to 'peregrine sheet' described in the general splashing literature [5]. Figure 1(a) and (b) shows an irregular peregrine sheet from an earlier study and a typical sheet structure observed in the cold modeling experiment respectively. From high speed video, droplet formation process was observed and three stages could be identified- amplitude of the waves (which will be called 'sheets' from now on) enlarged at the edge of the cavity, instability grew formed at the rim of the sheets and fingers were formed and finally, fingers broke up into one or number of droplets. Depending upon lance height and air flow rate, any one or two or all three stages were found. For example, at gas flow rate 40 L/min and lance height 150 mm, only sheet structures were observed. As gas flow rate increased from 40 L/min to 50 L/min, fingers as well as droplet generation began. It was observed that frequency and amplitude of the waves in the cavity, the height of the sheets increased as gas momentum on bath surface increased which ultimately, increased droplet generation. Also, the shape of the droplets changed from circular to irregular shapes as momentum of impact jet grew. It was found that the characteristics of the waves have an effect on the splashing droplet amount and shape. A variety of mathematical techniques (including Fast Fourier Analysis) were used to analyze the wave behavior and the results from this analysis will be discussed at the symposium.