Effects of the geometrical configuration of air–water mixer on the size and distribution of microbubbles in aeration systems

Abstract

The objective of this work is to present a novel geometrical configuration for microbubble generators (MBGs) to improve dissolved-oxygen levels in water.Among various methodologies from the literature, Orifice and Venturi tubes have been considered as baseline cases. Experimental data from the literature are used to verify a computational fluid dynamics (CFD) case developed for a better understanding of the dynamics of MBGs. As a result, the validated CFD setup has been implemented on a modified Venturi-type generator, where air is injected coaxially with respect to the tube axis, whereas a helicoid wall at variable pitch angle is used. Results show a reduction in the mean bubble diameter distribution from the baseline Venturi tubes, particularly, at lowspeed inlet velocities. This is of interest, especially to decrease the energy requirement for most common water aeration systems.

A review on bubble generation and transportation in Venturi-type bubble generators

“…1(d), owns advantages of simple structure, installation convenience, having no internal moving parts, less maintenance, and good reliability. Most importantly, low power consumption makes it an economic alternative for enhancing gas-liquid mass transfer (Terasaka et al, 2011;Basso et al, 2018). A Venturi bubble generator is capable of generating a high number density of micro or fine bubbles normally with a mean diameter below 100 μm (Fujiwara et al, 2003;Kawamura et al, 2004;Yoshida et al, 2008;Kaneko et al, 2012), and the concentration and size of produced bubbles in a wide range from tens of microns to millimeters are controllable by operating the liquid and gas flow rates.…”

Initial Results from the Experimental and Computational Study of Microbubble Generation

“…This work is based on our previous numerical model (Basso et al [23]) which was validated with numerical and experimental results from other designs of microbubble generators in the literature. MBGs performance is estimated in terms of Probability Density Function (PDF) of the microbubble diameter distribution, especially in the computation of the mean diameter -in relation with the levels of dissolved oxygen released in water.…”

“…The grid independence study has been discussed in details in our previous paper (Basso et al [23]) where the same CFD model is presented and fully-validated with previous experimental and numerical data from the literature. A valid mesh grid size had been estimated by varying the total number of elements in the grid domain and by keeping the same inflation layer ratio near the wall.…”

Influence of diffuser design on selected operating variables for wastewater flotation systems: a review

“…as nanobubbles with a diameter of less than 0.2 microns, while microbubbles have a diameter of 10-100 microns and lastly, macro bubbles that have a diameter of greater than 100 microns which tend to rise faster than the rest. Moreover, microbubbles are of interest in water and wastewater treatment as nanobubbles take longer to rise to the top while macro bubbles are inefficient due to their high rising velocity (Sadatomi et al 2005;Basso et al 2018). They have adsorbent properties as they can adsorb and agglomerate particulate matter due to their bigger surface area and their negative charge (Lee et al 2019) which neutralizes repulsion forces between suspended matter.…”

“…Bubble size is influenced by diffuser design and affects bubble particle collision thus attachment of suspended solids including the rise velocity which affects the efficiency of the system (Edzwald 2010). The size is governed by a sparging rate, pore size and also the wastewater parameter-volumetric quality and mixing velocity (Basso et al 2018). Most researchers have focused their work on micro and nanobubbles in a bid to improve the efficiency of flotation systems.…”