Chemically Reactive Transport in imperfect Hele-Shaw cell: 2-Phase Flow Experiments and Simulations

Access to clean water is one of today’s major global challenges. Human health, food production and biodiversity all rely on groundwater, yet this vital resource is increasingly exposed to soil pollution. Substances such as pesticides, fertilizers, plastics and industrial chemicals seep into the ground and travel downwards with rainwater. Before reaching groundwater, pollutants must pass through soil layers that act as natural filters. These layers can slow down or transform contaminants, but their effectiveness is uncertain. Predicting whether pollutants stay trapped in the soil or reach aquifers remains a central unresolved problem in environmental science.

A key difficulty is that soils are highly heterogeneous. They contain pores and grains of different sizes, shapes and chemical properties, producing complex flow pathways where some regions transmit water rapidly while others remain stagnant. Most soils are also only partly saturated, with water coexisting alongside pockets of air. These air–water–solid interfaces strongly influence motion and mixing, often causing pollutants to spread in irregular, non-predictive ways. How all these processes combine under partially saturated conditions remains poorly understood.

This work aims at addressing this gap through controlled experiments and advanced simulations. The experimental work, uses a transparent soil analogue known as a Hele-Shaw cell: two glass plates separated by a thin gap and patterned with microstructures that reproduce aspects of natural soil heterogeneity. By injecting water, air, and chemical solutes into the cell and filming their movement with high-sensitivity cameras, I observe pollutant pathways and reactions directly under realistic but fully controlled conditions. Unlike standard column tests, this approach provides real-time visualization over large areas while still resolving fine spatial details.

This poster presents my preliminary work for the study chemical reactions in partially saturated soils, examining how structure and water content affect reaction rates when reactions are fast compared to molecular mixing. These experiments are complemented by detailed simulations using OpenFOAM, more specifically a solver developed by Krishna et al. By reproducing flow patterns in the Hele-Shaw cell and modeling chemical transport within them, the simulations help identify which microscopic processes most strongly control large-scale behavior.