Oil filaments produced by an impeller in a water stirred thank

TL;DR

This study visually analyzes how an impeller disperses oil in water, revealing the formation of viscous filaments and drops, with detailed flow dynamics at a fixed Reynolds number of 24,000.

Contribution

It provides a detailed visualization and description of oil filament formation and dispersion mechanisms using a Scaba impeller in turbulent water flow.

Findings

Viscous oil filaments are generated and broken into drops.

Flow regions are characterized by high turbulence near the impeller and low turbulence elsewhere.

Drops become spheroidal due to surface forces in low-velocity zones.

Abstract

In this video, the mechanism followed to disperse an oil phase in water using a Scaba impeller in a cylindrical tank is presented. Castor oil (viscosity = 500 mPas) is used and the Reynolds number was fixed to 24,000. The process was recorded with a high-speed camera. Initially, the oil is at the air water interface. At the beginning of the stirring, the oil is dragged into the liquid bulk and rotates around the impeller shaft, then is pushed radially into the flow ejected by the impeller. In this region, the flow is turbulent and exhibits velocity gradients that contribute to elongate the oil phase. Viscous thin filaments are generated and expelled from the impeller. Thereafter, the filaments are elongated and break to form drops. This process is repeated in all the oil phase and drops are incorporated into the dispersion. Two main zones can be identified in the tank: the impeller discharge characterized by high turbulence and the rest of the flow where low velocity gradients appear. In this region surface forces dominate the inertial ones, and drops became spheroidal.