Catastrophic phase inversion in high-Reynolds number turbulent Taylor--Couette flow

TL;DR

This study investigates how catastrophic phase inversion occurs in highly turbulent Taylor--Couette flow of oil-water emulsions, revealing dramatic changes in morphology and rheology despite turbulent conditions.

Contribution

It demonstrates the triggering of phase inversion in turbulent flow and analyzes the resulting changes in emulsion properties using torque measurements and microscopy.

Findings

Phase inversion can be triggered by varying void fraction.

Effective viscosity can be significantly higher or lower than individual components.

Global torque response appears Newtonian despite turbulence.

Abstract

Emulsions are omnipresent in the food industry, health care, and chemical synthesis. In this Letter the dynamics of meta-stable oil-water emulsions in highly turbulent ($10^{11}\leq\text{Ta}\leq 3\times 10^{13}$) Taylor--Couette flow, far from equilibrium, is investigated. By varying the oil-in-water void fraction, catastrophic phase inversion between oil-in-water and water-in-oil emulsions can be triggered, changing the morphology, including droplet sizes, and rheological properties of the mixture, dramatically. The manifestation of these different states is exemplified by combining global torque measurements and local in-situ laser induced fluorescence (LIF) microscopy imaging. Despite the turbulent state of the flow and the dynamic equilibrium of the oil-water mixture, the global torque response of the system is found to be as if the fluid were Newtonian, and the effective viscosity of the mixture was found to be several times bigger or smaller than either of its constituents.