Vortex–Swirl Flow Results in Microbubble-Enhanced Transient Water Properties: A Time-Resolved Analysis from Fine-Bubble Engineering

Abstract

The inward vortex–swirl-type motion of convective, rectilinear water flow has been studied vis-à-vis its propensity for bubble formation, with a particular focus on the microbubble region. It has been found that a large population of smaller microbubbles, around 1 μm in diameter, is created in the process of these types of motions, and the time-dependent behaviour of this “micro-bubbly” water is analysed as Stokes’ law for microbubble dissipation occurs, such as bubble population, dissolved oxygen, pH, etc. Exponential decay analysis on the DLS-measured microbubble populations gave relaxation times τ of ~2.4 h and 3.6 h in exp(−t/τ) fits for DI and filtered tap water, respectively. The downward shift in pH was about 0.08 ± 0.016 and 0.11 ± 0.018 for DI and filtered tap water, respectively. For DI water, the level of dissolved oxygen (DO) at room temperature of 19 °C was ~102% at “t = 0”, and it declined to ~87% within 3 h (with the unprocessed background sample being about 84 ± 1.1%). The respective DO decay results in the case of the filtered tap water (at 19 °C) were ~105% at “t = 0”, declining to 91% within 3 h (background = 86 ± 1.2%). This allows for the dynamic properties to be understood in the context of how microbubbles determine the observed properties of post-flow water, including rationalising the observations of its time-transient properties. Naturally, this may well be of interest in gas transfer optimisation in the growing field of “fine-bubble engineering”.