PoreFlow: Visualizing multiphase flow in porous media with neutron imaging

Being able to resolve the flow of liquids within opaque porous materials is important in order to solve a series of pressing societal challenges. Examples include freshwater supply, handling of contaminants in soil, and the administering of drugs in living tissue. X-ray based CT is increasingly used to perform 3D microscopy of what porous materials look like inside, with a spatial resolution tpically around one micrometer. Owing to low contrast when using X-rays, it can be challenging to study liquids within the pores. Neutrons can be used as an alternative to X-rays to look inside materials. An advantage of neutrons is that they in many situations give increased contrast when studying liquids. Fazel Mirzaei is hired as PhD candidate in the PoreFlow project. He is currently doing his compulsory course work, but also performing experiments both at our home laboratory, at synchrotrons and at neutron sources (PSI and ILL). In 2021 we have carried out neutron-CT where we have studied rocks being dissolved when exposed to salts (KCl). These experiments are important to better understand and predict for example landslides and quick clay. Moreover, we are currently working on planning a neutron-based CT experiment to follow in situ the development of frost heave processes under realistic laboratory conditions. Frost heave is a phenomenon which gives extensive damage to buildings and infrastructure with substantial socio-economic cost. The PoreFlow project is carried out as an integrated part of CoE PoreLab, which has flow in porous media as a main research topic. This research is important to understand liquid transport in soil, porous rocks and living tissue ? all themes of high relevance in the unfolding climate crisis.

Understanding liquid flow in porous materials is key to resolving a range of pressing societal challenges, including fresh water supply and contamination in soil and rocks, as well as drug administration in living tissue and biomedical devices. During the last few years, tremendous progress in the physics of porous media has been made both theoretically and experimentally. X-ray computed tomography (CT) now allows 3D microscopic imaging of the interior of opaque porous materials, with resolution often better than 100 nm. Still, owing to the weak interactions between X-rays and light elements, it remains difficult to obtain information about liquids inside the pores, not to mention their dynamics. In the PoreFlow project, as part of CoE PoreLab, we aim to exploit the inherently higher sensitivity to light elements offered by neutrons to quantitatively monitor liquid dynamics in porous materials in 3D and real time. A top international team with complementary know-how in the fields of physics, neutron imaging, geophysics and life sciences has been assembled, including five Norwegian professors from NTNU, UiO and USN. Starting out with idealized test systems based on microfluidics combined with inert bead packs, the project aims to ultimately image liquid transport in soil, porous rocks and tissue. An important ambition is to challenge existing theories on two-phase flow, including recently published works describing fluctuations in the steady state. PoreFlow is of high relevance to the upcoming European Spallation Source (ESS), and an expressed aim of the project is to prepare Norwegian user communities within the physics, geo- and lifesciences, including relevant industries, for the upcoming new possibilities offered by ESS. In summary, the project aims to contribute to the understanding of multiphase flow in porous media through innovative use of neutron computed tomography - a topic with profound scientific and societal consequences.