Reversal of effects from gel production in a reacting flow dependent on gel strength

In reacting flows where chemical reactions occur within a flowing fluid, certain changes in the properties of the fluid, induced by the chemical reaction, can alter the flow dynamics. Generally, the most significant changes in the flow characteristics are associated with the largest changes in the fluid properties induced by the reaction. Specifically, the flow changes monotonically in response to the change in the physical properties induced by the reaction. However, this paper demonstrates a reacting liquid flow where the effect on the flow reverses in response to changes in the physical properties. We experimentally investigated viscous fingering (VF) in a reacting flow where the chemical reaction produces a gel. VF is a phenomenon wherein the interface of two fluids is fluid-dynamically unstable and forms a fingerlike pattern when the more-viscous fluid is displaced by the less-viscous one in porous media or Hele-Shaw cells. Rheological measurements of the gel produced at the liquid-liquid interface demonstrate that gel production affects the VF dynamics in completely opposing manners, depending on the strength of the gel. The VF pattern is approximately the same as the nonreactive case when the gel strength is weak, the fingers become narrower when the gel strength is medium, and the fingers become wider when the gel strength is strong. These opposing trends cannot be explained by standard linear stability analysis for a reactive system where only the viscosity effect is considered. In this paper, we propose a model that explains these opposite effects via a stability analysis of the VF that considers the strength and viscoelastic properties of the gel. In the proposed model, the VF becomes thinner when the shear thinning viscosity of the gel is effective, whereas the VF becomes wider when the gel behaves as an elastic or solid material and, thus, acts to reduce the permeability of the porous media. The aforementioned viscoelastic properties are based on actual viscosity measurements of the gel bulk itself. Combining the experimental results and theoretical considerations, we demonstrate that it is possible to achieve opposite VF effects depending on the gel strength. This is enabled by the fact that the rheological properties, which are primarily responsible for the flow dynamics, change depending on the gel strength.

Automated summary

In this paper, the authors investigate the impact of chemical reaction-induced gel production on viscous fingering dynamics. They propose a model that explains the opposite effects observed and demonstrate that the rheological properties of the gel can lead to different flow patterns.