ISTOPore Seminar by Kevin Pierce

Abstract

Solute mixing is ubiquitous in the water-filled layers of soil and fractured rock near the Earth’s surface, where it controls chemical reactions, contaminant transport, and nutrient delivery to plants and bacteria. Although mixing is well-studied in unconfined flows, our understanding remains limited in flows through porous media, especially when air and water coexist in the pore space. In this talk, I will describe my recent experiments on solute mixing in porous media. The experiments directly image fluorescent chemicals in transport through porous models, enabling space and time resolution of chemical concentration fields. The transparent models are fabricated by stereolithography 3D printing. I will discuss (a) the dependence of solute mixing rates on the solid structure of the porous medium and (b) the impact of a moving air-water interface on mixing during the drainage of the model. The single-phase experiments show that increased disorder in the porous structure only weakly enhances mixing, in contrast to theory developed for unconfined flows. The multi-phase experiments demonstrate that drainage flows enhance mixing compared to single-phase flows in identical porous geometries. I will discuss the mechanics generating these observations and describe implications for the transport of chemicals in the subsurface.