Microscale Chaotic Mixing as a Driver for Chemical Reactions in Porous Media.

Area of Science:

• Environmental science
• Geochemistry
• Fluid dynamics

Background:

• Mixing-induced reactions are crucial for subsurface biogeochemical processes and contaminant transport.
• Pore-scale fluid flow exhibits chaotic mixing, influencing concentration gradients and mixing rates.
• The impact of pore-scale chaotic mixing on chemical reaction rates remains largely unknown.

Purpose of the Study:

• To investigate the effect of pore-scale chaotic mixing on chemical reaction rates.
• To compare experimental findings with classical macrodispersion models.
• To develop a predictive model for mixing-induced reactions in porous media.

Main Methods:

• Utilized refractive index matching and laser-induced fluorescence imaging.
• Studied a bimolecular redox reaction to quantify reaction rates.
• Developed and validated a reactive transport model.

Main Results:

• Classical macrodispersion models overestimate reaction rates due to incomplete mixing.
• Microscale chaotic mixing exponentially increases the mixing interface and reaction rates.
• Reaction product formation is directly controlled by chaotic mixing dynamics.

Conclusions:

• Chaotic mixing is a primary factor controlling reaction rates in porous media across various scales.
• The developed model accurately captures experimental results and predicts reaction behavior.
• Findings offer a new framework for understanding environmental compound fate and transport.