Mixing in Multiphase flows through Microporous Media

When you add milk to a cup of coffee you can efficiently mix the components by stirring with a spoon: the system is brought from a state of separation – where the coffee and the milk exist in separate domains – to uniformity – where the coffee and milk are indistinguishably blended. In porous media such as soil and rock it is the complicated flow paths that dictate how efficient the mixing is. In multiphase flow – when two or more liquids or gases are flowing together through the pores – the flow will vary in complex ways both in time and space, and we so far know very little about how the mixing occurs under these circumstances. In this project, we investigate the mechanisms behind, and establish physical explanations for how mixing occurs in multiphase flow through porous media. We approach this interdisciplinarily by combining novel numerical, experimental and theoretical methods. A postdoc has developed a unique fluorescence-based experimental rig for precisely imaging concentration distributions at the pore scale. We have developed robust and efficient numerical simulation tools and investigated how multiphase flow influences spreading and mixing of chemicals. The results show that spreading and mixing is strongly enhanced by the motion of the interface between the phases, which may have far-reaching consequences for transport in partially water-saturated soil. We are concurrently investigating simplified models to explain these findings theoretically.

Mixing is the operation by which a system is brought from segregation to uniformity. Solute mixing exerts an important influence on chemical reactions by bringing reactants in contact. It thus controls processes across a wide range of natural and industrial porous systems; spanning from CO2 sequestration in deep aquifers, to drug delivery in the human body. Recent work has shown that the mixing dynamics in porous media are chaotic, implying that fluid elements are elongated at an exponential rate, potentially changing reaction rates by orders of magnitude compared to the predictions of conventional models. However, despite its ubiquity, very little is currently known about solute mixing in multiphase flows, i.e. when two or more phases are flowing together in a porous medium. Only very recently have the numerical methods, experimental techniques and theories of related systems reached a level of maturation where a quantitative investigation of these processes is feasible. In the project M4, I will develop a new theoretical framework for understanding and exploiting how multiphase flow controls mixing in porous media. To achieve this goal, I will develop numerical methods for highly accurate simulation of mixing in multiphase flows. With my collaborators, I will design and execute novel experiments imaging solute mixing in 3D porous media and microfluidic geometries. The output will include fundamental knowledge of how mixing occurs in a wide class of systems, open-source computational tools and novel microscale mixer designs. M4 brings together world-leading, complementary expertise on its two key ingredients: multiphase flow and mixing in porous media. It involves partners from the Universities of Oslo and Rennes and SINTEF Digital, and is an interdisciplinary collaboration unifying theoretical, numerical and experimental approaches, building on nonlinear dynamics, fluid mechanics and computer science, with perspectives to the many applications of microfluidics.