Why Gas Content Matters for Cavitation: The Hidden Role of Tiny Gas Bubbles
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Cavitation plays a key role in many technologies – from ultrasonic cleaning to chemical processing – but can behave unpredictably depending on the quality of the liquid. It is influenced not only by dissolved gases, but also by small undissolved gas bubbles.
This often overlooked aspect was revealed by researchers from the Laboratory for Hydraulic Machines (LVTS) at the Faculty of Mechanical Engineering, University of Ljubljana. The results of the study will help improve the understanding of cavitation and enhance the repeatability and efficiency of cavitation-based systems in both industry and research.
The gas content of a liquid is a fundamental indicator of liquid quality and a key factor influencing cavitation behaviour. Despite its importance, gas-related effects are frequently overlooked in both cavitation research and industrial applications, where liquids are often assumed to be comparable. In practice, gas content is typically assessed only through dissolved gas measurements using sensors, while undissolved gas bubbles present in the liquid are often overlooked. This study highlights the limitations of relying solely on dissolved gas measurements in cavitation studies.
By comparing liquids with different dissolved gas levels, as well as liquids with identical dissolved gas levels but different concentrations of tiny air bubbles (<200 µm), this work demonstrates that gas content strongly affects both cavitation inception and its developed state. High-speed observations and acoustic measurements show that in undersaturated liquids, cavitation can initiate from a single nucleus and generate stronger collapse-related acoustic noise. In contrast, the presence of undissolved gas bubbles promotes earlier and more organised cavitation structures while reducing acoustic intensity. These effects disappear once the bubbles are removed, demonstrating that dissolved gas alone cannot fully represent gas-related influences on cavitation.
The study therefore suggests that future cavitation research and industrial applications should consider both dissolved and undissolved gas content to achieve more reliable control and understanding of cavitation. In doing so, the research contributes to the development of more advanced industrial technologies and to a more efficient and responsible use of resources, for example in cleaning and liquid treatment processes.
The results of the study were published in the journal Ultrasonics Sonochemistry (IF=9.7): The importance of (un)dissolved gases on early-stage cavitation dynamics within an acoustic field.
