Anomalous front broadening during spontaneous imbibition in a matrix with elongated pores

Abstract

During spontaneous imbibition, a wetting liquid is drawn into a porous medium by capillary forces. In systems with comparable pore length and diameter, such as paper and sand, the front of the propagating liquid forms a continuous interface. Sections of this interface advance in a highly correlated manner due to an effective surface tension, which restricts front broadening. Here we investigate water imbibition in a nanoporous glass (Vycor) in which the pores are much longer than they are wide. In this case, no continuous liquid-vapor interface with coalesced menisci can form. Anomalously fast imbibition front roughening is experimentally observed by neutron imaging. We propose a theoretical pore-network model, whose structural details are adapted to the microscopic pore structure of Vycor glass and show that it displays the same large-scale roughening characteristics as observed in the experiment. The model predicts that menisci movements are uncorrelated, indicating that despite the connectivity of the network the smoothening effect of surface tension on the imbibition front roughening is negligible. These results suggest a new universality class of imbibition behavior, which is expected to occur in any matrix with elongated, interconnected pores of random radii.liquid imbibition | interface roughening | porous media | neutron radiography | computer simulations M any everyday processes involve the flow of a liquid into a porous matrix, for instance, when we dunk a biscuit into coffee, clean the floor with a cloth, or get drenched with rain. The same process is also important in nature (e.g., for water to reach the tips of the tallest trees or to flow through soil) and crucial for different industrial processes, ranging from oil recovery and chromatography to food processing, agriculture, heterogeneous catalysis, and impregnation (for reviews see refs. 1-4).The above processes are examples of imbibition (Fig. 1). Imbibition of a liquid into a porous matrix is governed by the interplay of capillary pressure, viscous drag, volume conservation, and gravity. The porous matrix often has a complex topology. The inhomogeneities result in variations in the local bulk hydraulic permeability and in the capillary pressure at the moving interface. Nevertheless, the invasion front during solely capillarity-driven (i.e., spontaneous) imbibition advances in a simple square-rootof-time manner, according to the Lucas-Washburn law (5, 6). Such behavior is a result of the time-independent mean capillary pressure and the increasing viscous drag in the liquid column behind the advancing front. It is valid down to nanoscopic pore sizes (7-9) and particularly robust with regard to the geometrical complexity of the porous matrix (1, 4, 10, 11). The evolution of the invasion front displays universal scaling features on large length and timescales, which are independent of the microscopic details of the fluid and matrix (12-18), and which parallels the elegance of critical phenomena.Typically imbibition is studied using paper (14-16) or...

Capillarity-Driven Oil Flow in Nanopores: Darcy Scale Analysis of Lucas–Washburn Imbibition Dynamics

“…This results in changes in the light refraction at the advancing imbibition front. In combination with the cylindrical matrix shape this leads to an apparent macroscopic meniscus at the advancing oil front in an optical imaging experiment and thus allows one to track, in principal by bare eye, the imbibition front moving in the porous glass [68], [31] [48].…”

Effects of microstructure on water imbibition in sandstones using X‐ray computed tomography and neutron radiography

“…More importantly, recent technical improvements in neutron imaging provide adequate spatial and temporal resolution to trace water flow and to obtain quantitative information on moisture content. Researchers have observed temporal changes in the spatial distribution of water in rocks [Dewanckele et al, 2014;Kang et al, 2013], soil [Carminati et al, 2008;Tullis et al, 1994], ceramics [Zhang et al, 2010], sand [Deinert et al, 2004;Vasin et al, 2008], bricks [Czachor et al, 2002;El Abd et al, 2009;Karoglou et al, 2005], and even nanoporous glass [Gruener et al, 2012] using two-dimensional (2-D) neutron radiography and three-dimensional (3-D) tomography. These measurements have been conducted at various centers worldwide-at Oak Ridge National Laboratory in the USA, Paul Scherrer Institute in Switzerland, Helmholtz-Zentrum Berlin in Germany, and the Institute Laue Langevin in France [Hall et al, 2010;Hassanein et al, 2006;Perfect et al, 2014].…”

Capillary Action in Scalar Active Matter

“…So far the transport properties of interacting and non-interacting active particles in heterogeneous media under both quiescent and flow conditions [27][28][29][30] have been studied. To the best of our knowledge, the classical experiment of spontaneous imbibition of a liquid into a porous medium [31,32] has not been performed in the context of active fluids up to now.…”