Peeking into pores
23 Jui 2026A powerful synergy of in-situ neutron imaging and numerical models gives rise to a novel model describing water vapour condensation in porous materials
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Environnement
Water molecules are tiny and able to move very quickly through materials, even those that, at first glance, may appear impenetrable. This includes many porous materials. Understanding how water condenses within porous rocks is essential to grasp the impact of condensation on material functionality for future underground storage solutions.
In a recent study combining a novel, highly comprehensive model of water condensation with experimental data obtained on ILL’s neutron tomograph NeXT, scientists were able to obtain a highly precise description of this phenomenon. Neutron imaging data were used to validate the numerical model by comparing simulations with experimentally observed water distributions. The model was then shown to reproduce condensation behaviour not only in relatively homogeneous samples, but also in more realistic complex porous materials, including heterogeneous structures and samples containing small fractures. Future works will exploit the new microtomography capabilities of the PorTo instrument to dive deeper into the microscale nature of the problem, expanding the study to various domains, such as those relevant to thermal management and energy production.
How condensation affects everyday materials
Many materials that surround us on a daily basis are exposed to environmental humidity and, subsequently, the condensation of water on their surfaces or within their internal structure. These range from fuel-cell diffusion layers and metal foams for heat exchangers to construction materials and soil systems. An important example are porous and fractured rock systems, which play a key role in future large-scale hydrogen storage and transport solutions. Due to a heterogeneous porous nature, rock formations have a particular propensity for fluid uptake and retention which significantly influences their transport property and can interfere with efficient storage capacity and functionality. A detailed understanding of the mechanisms underlying moisture condensation in porous materials is therefore essential for many different phenomena.
Modelling condensation: a complex challenge
Despite being omnipresent in everyday life, condensation is an extremely complex process and the development of models to describe it appropriately has been highly challenging. Until now, such models have mostly divided condensation into two processes: diffusion (the propelling of water along a substrate, such as sandstone, due to the random, turbulent motion of water molecules) and advection (the passive motion of water along the substrate). The separation of these two terms limited the precision and generalisability of the models developed so far, and the quest for a unifying approach became increasingly urgent.
In a recent study performed by researchers from the Laboratoire des Écoulements Géophysiques et Industriels in Université Grenoble-Alpes, the Laboratoire de mécanique multiphysique et multiéchelle in Lille, and the ILL, advection and diffusion were combined via a sophisticated, yet simplified numerical approach. To this end, the scientists defined a so-called effective Péclet number to describe how both heat and vapour transport influence the rapid movement of the liquid front along a model porous material. In addition, they introduced a so-called capillary number for a comprehensive description of the different forces governing the condensing liquid in different regions of the pores.
Watching water move through stone with neutron imaging
Importantly, the team was able to directly validate their model by performing neutron imaging experiments on ILL’s instrument NeXT. The scientists used sandstone samples into which they injected water vapour under precise, well-controlled experimental conditions. The team was able to exploit a well-known advantage of neutrons: their strong interaction with hydrogen, which allows for precise visualisation of the water front moving along the sandstone samples, thereby providing information that cannot be obtained using other experimental techniques.
Neutron tomography images, shown in the top row, reveal how water accumulates inside fractured porous sandstone over time. The bottom row shows the corresponding numerical model, which closely reproduces the experimental observations at 500, 1000 and 1500 seconds. The axes indicate position within the sample, and the colour scale represents water content.
By feeding experimentally obtained results back into their model, the team was able to eventually obtain the best possible agreement between theory and experiment. Notably, they found that the model also held for heterogeneous substrates and those including fractures, i.e. tiny cracks, which is an excellent representation of real-life materials.
This study, which was recently published in the International Journal of Heat and Fluid Flow, and is part of ongoing research conducted over the last 7 years, demonstrates how elegantly theory and neutron-based techniques complement each other in the quest for describing crucial everyday phenomena - even those that may appear too complex to describe.
Reference: Nemati, A., Séchet, P., Lukić, B., & Briffaut, M. (2026). Numerical modelling of heat and mass transfer during vapour condensation in porous media: Insights from neutron tomography. International Journal of Heat and Fluid Flow, 119, 110293. DOI: 10.1016/j.ijheatfluidflow.2026.110293
ILL Contact Person: Bratislav Lukić
Institutions involved in the research: Université Grenoble Alpes, LaMcube