Bubble nucleation from micro-crevices in a shear flow

Abstract

The formation of gas bubbles at gas cavities located in walls bounding the flow occurs in many technical applications, but is usually hard to observe. Even though, the presence of a fluid flow undoubtedly affects the formation of bubbles, there are very few studies that take this fact into account. In the present paper new experimental results on bubble formation (diffusiondriven nucleation) from surface nuclei in a shear flow are presented. The observed gas-filled cavities are micrometre-sized blind holes etched in silicon substrates. We measure the frequency of bubble generation (nucleation rate), the size of the detaching bubbles and analyse the growth of the surface nuclei. The experimental findings support an extended understanding of bubble formation as a self-excited cyclic process and can serve as validation data for analytical and numerical models.

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

“…It has been demonstrated that nucleation rate (frequency of bubble production) and the volume of the detaching bubbles show a non-linear dependence on the shear rate, in particular, higher flow rates over artificial nucleation sites lead to detachment of smaller gas bubbles. 100,162 This general and intuitive behavior was also observed in a micro-electrolyzer for water splitting. 163 It was also observed that with increased applied voltage, the bubbles detach at smaller radii, attributed to the influence of convection induced by detaching bubbles and electrostatic repulsions between the bubbles and the electrode.…”

“…For example, bubbles originating from an orifice on a wall detach at smaller radii with increased flow rates due to the induced shear stress. 99,100 It is thought that the detachment of bubbles from crevices can induce liquid jet formation into the crevice, filling it, and prevent further bubble growth (leading to the hysteresis described in the nucleation subsection). 80,101 Other methods to induce early bubble detachment are discussed in detail in section 4.…”

A versatile and membrane-less electrochemical reactor for the electrolysis of water and brine

“…The increased throughput with flow rate is intuitive since a higher flow rate exerts larger drag forces on the nucleated bubbles and, therefore, decreases their detachment size. 63 This implies that the percentage of catalyst surface area covered by bubbles in course of reaction is reduced, resulting in a larger number of reaction active sites. Furthermore, the volume fraction of gas is lower in a fast flowing liquid electrolyte.…”

Explanation of Bubble Nucleation Mechanisms: A Gradient Theory Approach

“…Similar diffusion driven nucleation has also been observed and extensively studied during cavitation. 35,36 Interfacial Free Energy in a Supersaturated Solution…”