Thin film flow: fluid transport via thin liquid films in slow porous media flows

The standard liquid transport processes in porous media happens through a network of interconnected pore bodies and pore throats (here called the primary network). When a non-wetting phase displaces a wetting phase from a porous sample (drainage), thin films of the wetting phase are bound to be left on the surface of the constituting grains (for example when air displaces water from a porous rock, thin films of water are left behind, covering the rock grains). Under certain conditions, isolated liquid films can eventually merge, forming a secondary network of interconnected films and capillary bridges (see red arrows in the figure) that can effectively enhance the overall connectivity of the medium and act as a new pathway for fluid transport. We have performed experiments using transparent networks with the objective of studying transport processes that are enhanced by film flow. Our setup allow us to directly visualize the secondary network in the sample and we have shown how fluid bodies that are not linked via the primary network can actually be connected via the secondary network. This connection has important consequences for processes such as the dispersion of pollutants in soils and the transport of nutrients to plants in arid regions.

 

 

References

Moura, E. G. Flekkøy, K. J. Måløy, G. Schäfer and R. Toussaint, “Connectivity enhancement due to film flow in porous media,” Phys. Rev. Fluids 4, 094102 (2019).

Moura, K. J. Måløy, E. G. Flekkøy, and R. Toussaint, “Intermittent dynamics of slow drainage experiments in porous media: Characterization under different boundary conditions,” Front. Phys. 7, 217 (2020).