Geometry-Induced Asymmetric Capillary Flow

Abstract

When capillary flow occurs in a uniform porous medium, the depth of penetration is known to increase as the square root of time. However, we demonstrate in this study that the depth of penetration in multi-section porous layers with variation in width and height against the flow time is modified from this diffusive-like response, and liquids can pass through porous systems more readily in one direction than the other. We show here in a model and an experiment that the flow time for a negative gradient of cross-sectional widths is smaller than that for a positive gradient at the given total height of porous layers. The effect of width and height of local layers on capillary flow is quantitatively analyzed, and optimal parameters are obtained to facilitate the fastest flow.

Rational design of capillary-driven flows for paper-based microfluidics

“…The procedure has been used in previous works to calculate the filling dynamics of porous substrates with different geometrical shapes. [16][17][18][19] It should be observed that we are reporting here a general formulation of the problem, which comprises the fluid imbibition of homogeneous porous media whose cross-sectional shape ‫)ݔ(ܣ‬ may vary in one, two or three dimensions, provided the flow is unidirectional. In what follows we describe typical examples of each case, on the base of specifically shaped paper sheets, as shown schematically in Table 1.…”

“…Paper sheets with different shapes have been proposed to pump fluids with a specific dynamics: circular, 13 rectangular, 14 trapezoidal, 15 sector-shaped, 16 and different combinations of them. [14][15][16][17] In most of the studies cited above, calculations to predict the instantaneous position of the meniscus in the substrate consider a geometrical shape designed beforehand. The procedure is also used in the analysis of capillary imbibition of porous materials other than paper, 18,19 and it is a direct calculation from a mathematical point of view.…”

The fastest capillary penetration of power-law fluids

“…The manipulated capillary flow in non-uniform porous structures, in terms of the evolution of flow distance to time, deviates from the classical Washburn equation based on uniform tubes (Reyssat et al, 2008(Reyssat et al, , 2009Shou et al, 2014bShou et al, , 2014c. As well, the fastest capillary flow on the basis of Newtonian fluids has been found in the optimally designed tubes and porous systems (Shou and Fan, 2015;Shou et al, 2014bShou et al, , 2014cShou et al, , 2014d. However, to our best of knowledge, less studies concern the development and optimization of the fast capillary-driven power-law fluids.…”

Branched polyethylene glycol/polypropylene micro-nanofiber nonwovens for fast liquid planar transmission

“…Generally, the introduction of nanofibers into the nonwovens is often utilized in strengthening the speed by enhancing the surface area. 6,7 Heterogeneous nonwovens, which were characterized with the branched networks made of micro-nanofibers, have been studied widely. [8][9][10][11] The branched network structure is common in nature, such as the vascular systems of animals, rivers, trees, and leaf veins of plants.…”