Turbulent droplet breakage in a von Kármán flow cell

Abstract

Droplet dispersion in liquid–liquid systems is a crucial step in many unit operations throughout the chemical, food, and pharmaceutic industries, where improper operation causes billions of dollars of loss annually. A theoretical background for the description of droplet breakup has been established, but many assumptions are still unconfirmed by experimental observations. In this investigation, a von Kármán swirling flow device was used to produce homogeneous, low-intensity turbulence suitable for carrying out droplet breakage experiments using optical image analysis. Individual droplets of known, adjustable, and repeatable sizes were introduced into an isotropic turbulent flow field providing novel control over two of the most important factors impacting droplet breakage: turbulence dissipation rate and parent droplet size. Introducing droplets one at a time, large data sets were gathered using canola, safflower, and sesame oils for the droplet phase and water as the continuous phase. Automated image analysis was used to determine breakage time, breakage probability, and child droplet size distribution for various turbulence intensities. Breakage time and breakage probability were observed to increase with increasing parent droplet size, consistent with the classic and widely used Coulaloglou–Tavlarides breakage model (C–T model). The shape of the child drop size distribution function was found to depend upon the size of the parent droplet.

Role of viscosity in turbulent drop break-up

“…Several models consider dimensional units (Martinez-Bazan et al 2010;Qi et al 2020), complicating the comparisons between different configurations and missing some hidden controlling parameters, while empirical formula, with important assumptions in the models not rigorously verified, have been applied outside their initial fitting range (Tsouris & Tavlarides 1994;Andersson & Andersson 2006;Martinez-Bazan et al 2010). Recent computational work has investigated various aspects of the break-up of drops in turbulent flow, including long bubble lifetime near critical conditions and limits of the Hinze-scale concept (Vela-Martín & Avila 2022), the interaction of turbulence cascade and the break-up dynamics in steady-state turbulent emulsion configuration (Crialesi-Esposito et al 2022;Crialesi-Esposito, Chibbaro & Brandt 2023), while experimental work has discussed the role of small-scale eddies in bubble break-up (Qi et al 2022) or drop break-up in a von Kármán flow (Ravichandar et al 2022). Separately, atomization of jets has received considerable attention, with analysis of the subsequent instabilities controlling the scale selection, break-up and drop-size distribution (e.g.…”

“…2022) or drop break-up in a von Kármán flow (Ravichandar et al. 2022). Separately, atomization of jets has received considerable attention, with analysis of the subsequent instabilities controlling the scale selection, break-up and drop-size distribution (e.g.…”

Experimental study on the differences between bubble and drop breakages in agitated turbulent flows

“…To verify these models, a large number of experimental data on fluid particle breakage are required. Several studies have reported experiments of breakage frequency and DSD for bubble and drop, respectively 12,22–42 (summarized in Tables S3.1 and S3.2). Some experiments showed that the breakage frequency monotonically increased with increasing fluid particle size 12,23–30 .…”

“…Their experiment showed that the breakage frequency first increased to a maximum and then decreased when the drop size increased. Herø et al 32 and Ravinchandar et al 34 performed the experiments on drop breakage in a vertical channel and a Von Kármán flow, respectively. The measured breakage frequency also showed the similar non‐monotonic trend when drop size increased even in the relatively lower dissipation rates of turbulent kinetic energy (please see Table S3.1).…”

“…But with increasing drop size, the local probability density of DSD in a specific interval of breakage volume fraction f V (i.e., f V = 0.44–0.55) decreased, and that in the interval of f V = 0–0.11 increased. Ravichandar et al 34 reported that the DSD of drop could be unimodal as a whole or transform from unimodal to bimodal shapes when drop size increased, which depended on the physical properties of dispersed phase. The profiles of DSD of bubble measured by Zhang et al 30 seemed to be U‐shaped or M‐shaped, and the probability of equal‐sized breakage increased with bubble size or agitation speed.…”