April 10, 2024

Listening to bubbles and other diversions

The ARC Research Hub for Australian Steel Innovation (Steel Research Hub) umbrellas many and varied research and development activities with our ten highly supportive industry partners, engaging in collaborative endeavours to tackle the intricate challenges faced by the steel industry. Amongst our nine innovative University Partners, Swinburne University of Technology (SUT) hosts the vibrant and passionate Professor Geoffrey Brooks, whose fascination with the symphony of sound from bubbles forming and collapsing makes for in-depth research. While some may regard this as an eccentric pursuit, for Geoff and the steel industry, it constitutes a matter of serious scholarly inquiry.

"Foams are an utterly mesmerizing phenomenon. Within a typical liquid foam, such as the remnants left in a sink post-dishwashing, bubbles coalesce, tethered by delicate liquid films gradually draining over time," Geoff elucidates, with an enthusiastic scholarly fervour.

"The intricate formations witnessed within these foams are truly remarkable, captivating the attention of mathematicians worldwide, owing to their profound implications in surface energy minimization." He pauses momentarily, as if contemplating the profound beauty inherent in the phenomenon, before continuing, "What's even more astonishing is the manifestation of foams in the steelmaking process, at temperatures well above 1600 degrees Celsius."

Indeed, the phenomenon of foaming holds profound significance in steelmaking processes, as numerous pivotal reactions crucial to steel production unfold within the slag foam above the molten steel. Yet, alongside this critical function lies a perilous propensity for sudden expansion and molten foam overflow, posing a significant safety hazard. Geoff conjures a vivid analogy, likening the spectacle to a molten milkshake cascading over the brim of a cup, albeit with hues of fiery crimson, an image both mesmerizing and alarming.

This unpredictable overflow behaviour, colloquially termed "slopping" in the steelmaking lexicon, poses a formidable challenge, exacerbated by the inherent difficulty in gauging the depth of the foam, thereby impeding pre-emptive measures to forestall overflow. One technique involves harnessing changes in sound intensity, reverberating above the vessel, to infer the height of the foam. Geoff elucidates this innovative approach, animatedly expounding on its principles, "The essence lies in the fluctuation of sound; the taller the foam, the more pronounced the attenuation in sound emanating from the gaseous injections beneath the foam." However, despite the conceptual elegance of this approach, precision measurements remain elusive. Undeterred, Professor Brooks, alongside his diligent protégé Jason Heenatimulla, embarks on a collaborative odyssey with talented engineers from BlueScope, endeavouring to refine existing monitoring systems. Their journey of discovery unfolds amidst a symphony of experimentation, deploying a cold model decked with strategically positioned microphones.

"We dedicate copious hours to the serenade of bubbles bursting into and out of existence," Geoff says. Expounding upon their methodology, Geoff articulates, "Our endeavour entails unravelling the fundamental principles governing sound propagation within foams, through meticulously controlled experiments conducted within the sanctuary of low-temperature environments. Subsequently, we endeavour to extrapolate our findings to the tumultuous milieu of industrial plant signals. So far, Jason Heenatimulla, a Steel Research Hub higher degree research candidate based at SUT, has been able to identify that high frequency sounds are likely to be the best for measuring foam height.”

As the study enters the exhilarating phase of plant trials, Jason finds himself immersed in the cacophony of bubbles emanating from the colossal expanse of a 300-tonne steel vessel, a testament to their unwavering commitment to unravelling the enigmatic allure of foams within the crucible of steelmaking.

Through this glimpse into the realm of steelmaking I find myself wholeheartedly concurring, that in the molten depths there exists an enigmatic, and multifaceted world encapsulated within bubbles, beckoning for further research to unravel the steel foaming mysteries.

Story by: Dr Sara Tomka – Hub Manager (Interim) Steel Research Hub