Generation of Small-Scale Bubbles at High Gas Concentrations via Cavitation

Abstract

Small-scale bubble research has drawn the interest of many researchers in the last 30 years, and several industries have found applications for which small-scale bubbles offer superior properties compared to macrobubbles, including the medical sector. The goal of this work is to develop a novel method of generating small-scale bubbles to treat hypoxia through the intravenous delivery of a bubbly, super-oxygenated saline solution. Oxygen delivery via small-scale bubbles has not successfully been achieved before due to the risk of an air embolism. The proposed machine utilizes high pressure to dissolve gas into a liquid. Once dissolved, bubble nucleation is then induced by forcing the fluid through a small restriction to cause cavitation. This design departs from past work as the gas and liquid are combined in a stream before the nucleation site. A comprehensive study of the resulting bubbly mixture is presented using a microscopy approach with automated image processing to study the size distribution of the small-scale bubbles downstream of the restriction. The influence of machine parameters, including gas saturation in the liquid, restriction geometry for cavitation, and compressor pressure, are quantitatively assessed using the Sauter mean diameter of the volumetric bubble size distribution. The distributions of all configurations show a strong collapse with the Sauter mean diameter. This captured the mean and standard deviations of thedistribution to provide a lower-order method of capturing machine parameters. This analysis is also used to reveal trends based on the influence of the machine parameters, which can be used to further reduce bubble sizes. Reducing the restriction geometry and increasing the compressor pressure for the given flow rate are identified as methods of reducing bubbles sizes. Quantitative analysis of these machine parameters based on optimization of dimensionless scaling coefficients resulted in a strong fit between the Sauter mean diameter and dimensionless machine parameters. An R^2 value of 0.98 for the given flow rate was achieved. The findings of this work indicate a strong influence of the residence time of the fluid in the restriction on the bubble size distributions. The findings from this work can be leveraged for further reducing bubble sizes for this method of bubble generation.