Recently, a faculty team from the School of Chemical Engineering and Technology at CUMT has made significant progress in the field of bubble dynamics research. Their findings, titled "Bubble coalescence principle in saline water," were published in the internationally renowned journal Proceedings of the National Academy of Sciences of the United States of America (PNAS). The first author of the paper is Li Danlong, a Ph.D. graduate of 2024 from CUMT Mineral Processing Engineering program. Researcher Zhang Haijun and CUMT’s Distinguished Professor Liu Qingxia, Academician of the Canadian Academy of Engineering, served as co-corresponding authors. CUMT is listed as the primary affiliation, with Shenzhen Technology University and the University of Alberta (Canada) as collaborating institutions. The paper was also selected for the PNAS Showcase.

Bubbles are ubiquitous in nature and human society, playing critical roles in mineral processing, environmental engineering, biomedicine, and other fields. The coalescence and rebound behaviors of bubbles after collision determine their stability in solution environments. While the inhibitory effect of ions on bubble coalescence has attracted extensive attention from researchers, theoretical breakthroughs in understanding the transition between rebound and coalescence dynamics in saline solutions have remained elusive.

Using a self-designed visual testing platform for freely ascending bubbles, the team revealed a key phenomenon: bubbles in saline solutions coalesce with free liquid surfaces within milliseconds after completing specific collision cycles. By comprehensively analyzing the contributions of ion characteristics and surface deformation, the researchers identified the upper limit of ion migration required for the rebound-coalescence transition. They calculated critical dimensionless parameter ranges—including the Eötvös number (Eo), Reynolds number (Re), and Weber number (We)—corresponding to different bubble dynamics behaviors in saline solutions. Additionally, the team explored the adjustable nature of ion-mediated coalescence inhibition and proposed a fundamental principle for bubble coalescence in saline solutions. This study enhances our understanding of bubble dynamics and transition mechanisms, offering critical insights for the controlled regulation of bubble lifetimes in solution environments and gas-liquid-solid flotation systems.

Paper Link:

https://doi.org/10.1073/pnas.2417043122