Removing proteins or bacteria on a tilted surface using air bubbles

TL;DR

This study investigates the use of air bubbles for cleaning proteins and bacteria from tilted surfaces, identifying optimal angles and bubble sizes, and analyzing the underlying shear stress mechanisms through experiments and numerical modeling.

Contribution

It provides new insights into the optimal conditions for bubble-based cleaning on inclined surfaces and combines experimental and theoretical approaches to understand the shear stress effects.

Findings

Maximum cleaning efficacy at surface angle of approximately 20° for polydisperse bubbles.

Shear stress analysis shows maximum shear force at about 22°, aligning with experimental results.

Optimal bubble size range identified as 0.3-2 mm radius.

Abstract

Cleaning surfaces with bubbles has been a topic of discussion in recent years due to the growing interest in sustainable methods for cleaning. Specifically, a method of using air bubbles to sanitize agricultural produce has been proposed as an eco-friendly alternative to current methods. 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 best cleaning efficacy at the surface angle of $\theta \approx 20^{\rm{o}}$ for polydisperse bubbles in the range of 0.3-2 mm and with an average radius of 0.6 mm in radius. To gain a better understanding of the underlying mechanism, we perform a numerical analysis of a single air bubble impacting surfaces with different angles. Our numerical and theoretical results show that the shear stress, which is proportional to the sliding speed but inversely proportional to the thickness of the film, results in the maximum shear force occurring at $\theta\approx22^{\rm{o}} \approx \pi/8$ which agrees well with the experiments.