The Slow Rise of Nanobubbles: A Dance Against the Current

Image credit: Mary Taiwo Ajide. Collection File: MTAG34

“For it is in the telling of a concept with a story that I am able to draw an in-depth understanding from its core meaning.” - Mary Ajide

This quote, which I’ve come to embrace as part of my academic voice, reminds me of the power of storytelling in unpacking complex ideas. Narrating a concept, particularly one as intricate as nanobubbles, through a story enables a more nuanced and comprehensive understanding of its foundational meaning. In simpler terms:

“I’ve found that when I explain a concept as a story, I really get to understand what it’s all about at its core.”

The title of this post was inspired by two whitepapers I authored on behalf of AquaB Nanobubbles Innovations Ltd, a spin-out company from the School of Chemical and Bioprocess Engineering, University College Dublin. These whitepapers reflect both the scientific and practical innovation embedded in nanobubble technology.

The first paper, “Nanobubbles for Enhanced Oil Recovery: How nanobubbles can increase recovery and improve efficiency,” offers a comprehensive overview of nanobubbles, emphasising their unique properties and wide-ranging applications. It explores their role in enhanced oil recovery, showcases AquaB’s cutting-edge electrostriction generation technology, and explains its underlying mechanism. It also highlights other applications in the oil and gas industry, contributing to the growing field of applied nanobubble engineering and its transformative potential in industrial processes.

The second paper, “Nanobubbles for Wastewater Treatment: How nanobubbles can increase efficiency, reduce costs and improve performance,” similarly outlines the transformative potential of nanobubbles. It focuses on wastewater treatment, detailing how nanobubbles can enhance treatment efficiency, lower costs, and improve performance. Like the first, it also highlights AquaB’s electrostriction technology and examines the broader field of applied nanobubble engineering, showcasing its potential for innovation and industrial impact.

So, I begin my narration – my beautiful tale – on The Slow Rise of Nanobubbles: A Dance Against the Current, where subtle forces unfold a story of resistance, patience, and possibility in motion.

The Slow Rise of Nanobubbles: A Dance Against the Current

Imagine a tiny bubble, so small that it is nearly invisible to the naked eye—this is a nanobubble. Despite their remarkable properties and vast potential across industries, one defining feature of nanobubbles remains: their surprisingly slow rise through a liquid medium.

At first glance, one might assume that the small size of nanobubbles would allow them to float effortlessly through liquids. However, their movement is far more complex. The slow-rising velocity of nanobubbles is a result of several interconnected factors that create a delicate balance of forces within the liquid. These forces work together to impede their upward journey, forcing them to rise at a much slower pace than their larger counterparts.

Buoyancy and Viscous Drag: A Tug of War

At the heart of this phenomenon lies buoyancy, the force that would typically push a bubble to the surface. In nanobubbles, however, this upward push is countered by viscous drag—the resistance experienced as the bubble moves through the liquid. This drag is particularly noticeable at the nanoscale, where the Reynolds number is low. Essentially, the fluid’s resistance against the nanobubble’s movement becomes significant, slowing its rise.

But that’s not all. The surface tension at the gas-liquid interface further complicates matters. This tension causes nanobubbles to deform from their spherical shape into an ellipsoid or a spherical cap, altering their hydrodynamic behaviour and making it even more difficult for them to move through the liquid. The combination of these forces creates a situation where nanobubbles rise at a pace that feels almost painstakingly slow.

Brownian Motion: A Random, Unpredictable Path

Adding another layer of complexity to the movement of nanobubbles is Brownian motion. At the nanoscale, the motion of these bubbles isn’t entirely predictable. Instead, they undergo random variations, causing fluctuations in their velocity as they rise. This randomness further delays the average rising velocity, contributing to the overall slow ascent of nanobubbles.

The Role of Liquid Properties

The properties of the liquid in which the nanobubbles exist also play a crucial role. The liquid’s density, viscosity, and temperature all influence how quickly nanobubbles can rise. Higher density and viscosity create greater resistance, making it harder for the bubbles to ascend. So, in liquids that are denser or more viscous, nanobubbles move even more slowly.

The Dance of Forces: A Lesson in Patience

In the world of nanobubbles, the slow rising velocity is not a limitation but rather a fascinating interplay of physical forces. The opposing forces of buoyancy and viscous drag, combined with surface tension and the random nature of Brownian motion, create a delicate, patient dance that delays their rise. Yet, this seemingly slow journey through the liquid medium allows nanobubbles to engage in unique interactions, making them invaluable in applications from water treatment to agriculture.

In essence, the slow ascent of nanobubbles isn’t simply a matter of speed; it’s a reflection of the intricate and fascinating behaviour that emerges at the nanoscale, where forces and characteristics interact in ways that larger objects can’t even begin to experience. And in this slow rise lies their potential—small, deliberate, and significant.

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I’ll close my post with this poetic reflection—a lyrical prose excerpt:

Unfolding complexity through narrative Revealing the depth through storytelling Where logic meets meaning And ideas find their voice - Mary Ajide

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Disclaimer: "Nanobubbles: Unveiling the Spectrum of Innovation" was originally published on the Nanobubble, Energy, Water: Pathways to Industrial and Environmental Sustainability All-Ireland Conference website