Growth and Arrest of Reactive Mixing Fronts from Spherical Point-Source Injections.

Area of Science:

• Environmental Science
• Chemical Engineering
• Fluid Dynamics

Background:

• Reactive processes in the environment often involve chemical front formation from point-source injections into a medium with another reactant.
• Bimolecular reaction fronts are well-studied in planar and cylindrical systems, but spherical configurations in 3D porous media are underexplored.
• Understanding these dynamics is critical for environmental applications, particularly subsurface solute transport.

Purpose of the Study:

• To experimentally investigate the dynamics of bimolecular reaction fronts in a spherical configuration resulting from point-like injection in 3D porous media.
• To analyze the formation of self-organized stationary reactive zones.
• To validate theoretical predictions for reactive front growth and arrest in 3D domains.

Main Methods:

• Utilized a bimolecular redox reaction within a hydrogel-based medium to simulate environmental reactive transport.
• Experimentally measured product distribution, front position, and product formation over time.
• Performed numerical simulations to analyze the impact of reactant diffusivity differences on front characteristics.

Main Results:

• Demonstrated the formation of a self-organized stationary sphere where the reactive zone maintains a fixed radius.
• Established that the stationary front radius scales linearly with flow rate and inversely with diffusion coefficient and concentration ratios.
• Identified new dynamical regimes in reactive transport influenced by reactant diffusivity.

Conclusions:

• Point-like injection in 3D porous media can lead to self-organized stationary spherical reaction fronts.
• Experimental data supports theoretical predictions for reactive front arrest in 3D.
• Highlights the necessity of full 3D modeling for accurate simulation of reactive transport in environmental applications involving point injections.