Sepideh Khodaparast - From Sticky Leaky Pistons to Sticky Rollers: Filtration/Cleaning Applications of Bretherton Bubbles
| Dates: | 9 March 2022 |
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| Times: | 14:00 - 15:00 |
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| What is it: | Seminar |
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| Organiser: | Department of Mathematics |
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| Who is it for: | University staff, External researchers, Current University students |
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Sepideh Khodoraparast (University of Leeds) joins us for this in-person seminar in the Physical Applied Mathematics Series
Abstract:
Originally studied by Bretherton and Taylor in 1961, the problem of estimating the thickness of the lubrication film around the gas bubble, based on the speed of the bubble, has been repeatedly revisited in the last decades. In this seminar, I will present experimental findings on Bretherton problem (motion of confined elongated bubbles) in the presence of flow and geometrical complexities at micro-scale and discuss how we can exploit our fundamental knowledge to develop new practical filtration and surface cleaning tools. In the absence of significant inertia and in channels of circular cross-sections, bubbles act as ‘sticky leaky pistons’ when exposed to the continuous flow of a micro colloidal suspensions: they collect larger particles and let smaller particles pass through. This unique capability is realised thanks to the fact that the thickness of the lubricating liquid film around the bubble is set by a single dimensionless number, namely the capillary number. In contrast, propagation of a gas bubble in a channel of rectangular cross-section no longer leaves a uniform liquid film on the channel wall. In this setting, the liquid film tends to leak from the central regions on the wall towards the corners. For sufficiently long bubbles at small capillary numbers, this cross-stream flow causes dry-out on the channel walls. Although risky for applications such as evaporative cooling, I will demonstrate how bubbles operating in this dry film regime can be used as ‘sticky rollers’ to effectively clean contaminated surfaces. Despite being a century-old problem, motion of a confined air bubble in laminar flow of a viscous liquid still raises challenging scientific questions while promising potentials when translated to applications.
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