Imbibition or drying dynamics: Controlled by big and small capillaries interconnectivity

In this work, we study the capillary rise mechanisms in heterogeneous porous material with different capillary sizes. Both theoretical and experimental work are performed to investigate the time evolution and the exchange at the interface of different porous media (different capillaries diameters). The first basic part contains the homogeneous capillary (without layer exchange), which is presented to distinguish the different characteristic times and the liquid capillary rise regimes. Considering gravity effect, shear stress and inertia, three regimes are distinguished theoretically and experimentally based on these two dimensionless parameters (Bo and Ga). Theoretical analysis and simulation results show the capillary rise in tendency and the appearance of oscillatory phenomenon. In the second part, the heterogeneous porous media are investigated. A multilayer domain is adopted to model the multiple distribution in capillary sizes. The interaction between these layers (different equivalent capillary sizes) demonstrate how the cooperation appears in nature so as to fit with the optimal situation of fast filling the porous media or the equivalent in drying. Experimental results on both homogeneous and heterogenous cases (corresponding to simple capillary rise and capillary rise with layer exchanges) have a favorable accordance with the theoretical analysis. The enhancement in imbibition has been demonstrated and explained as well.