Abstract
Cleaning surfaces with air bubbles in an aqueous medium has been a topic of discussion in recent years due to the growing interest in sustainable methods for cleaning biological surfaces such as agricultural produce. Specifically, in a bubble-injection method, inclined surfaces are targeted by many millimetric air bubbles that collide with and slide along the surface. The collision and subsequent sliding of these air bubbles exert shear stress on the surface, causing contaminants to be removed. The shear stress is proportional to the tangential speed of the bubble with respect to the surface divided by the thickness of the thin film of liquid between the bubble and the solid surface. In this study, we conduct experiments to test the cleaning efficacy at different angles of inclination of a contaminated surface. We use two different types of surface coated with either a protein solution or a bacterial biofilm. Our experimental results indicate that bubbles exhibit the highest cleaning efficacy at the surface angle of with respect to the horizontal plane for polydisperse bubbles in the range of 0.3–2 mm and with an average radius of 0.6 mm. To gain a better understanding of the underlying mechanism, we perform a numerical analysis of a single air bubble colliding with a clean surface at various angles. Our numerical and theoretical results show that the average shear force that the bubble exerts on the surface reaches a maximum at which agrees well with the experiments. We also compare the maximum shear stress in sliding phase with the shear stress required for removing different types of bacteria as a fluid-mechanics-based guideline for geometrical design of bubble cleaning devices.
5 More- Received 6 June 2022
- Accepted 14 March 2023
DOI:https://doi.org/10.1103/PhysRevFluids.8.043602
©2023 American Physical Society
Physics Subject Headings (PhySH)
Focus
The Optimal Angle for Cleaning with Bubbles
Published 28 April 2023
A stream of air bubbles can be most effective at cleaning produce or industrial equipment if it strikes at the correct angle.
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