Perspectives and design considerations of capillary-driven artificial trees for fast dewatering processes

The Fastest Capillary Flow in Root-like Networks under Gravity

Capillary flow has garnered significant attention due to its unique dynamic characteristics that require no external force. Creating a quantitative analytical model to evaluate capillary flow behaviors in root-like networks is essential for enhancing fluid control properties in functional textiles. In this study, we explore the capillary dynamics within root-like networks under the influence of gravity and derive the most rapid capillary flow via structural optimization. The flow time in a capillary is dominated by the capillary pressure, viscous pressure loss, and gravity, each of which exhibits diverse sensitivities to the structures of root-like networks. We scrutinize various structural parameters to understand their impact on capillary flow in root-like networks. Subsequently, optimal structural parameters (namely, the mother tube diameter and diameter ratio) are identified to minimize capillary flow time. Moreover, we discovered that the correlation between flow time and distance for capillary flow in root-like networks does not obey the classical Lucas-Washburn equation. These results affirm that root-like networks can enhance capillary flow, providing critical insights for numerous capillary-flow-dependent engineering applications.

Criteria for Crack Formation and Air Invasion in Drying Colloidal Suspensions

The drying of sessile drops of aqueous colloidal suspensions leads to the formation of a close-packed particle deposit. As water evaporates, a solidification front propagates from the edge of the drop toward the center, leaving behind a thin disk-shaped deposit. For drops with sufficiently large particle volume fractions, the deposit eventually covers the entire wetted area. In this regime, the dynamics of the deposit growth is governed by volume conservation across a large range of particle volume fractions and drying times. During drying, water flows radially through the deposit to compensate for evaporation over the solid's surface, creating a negative pore pressure in the deposit which we rationalize with a hydrodynamic model. We show that the pressure inside the deposit controls both the onset of crack formation and the onset of air invasion. Two distinct regimes of air invasion occur, which we can account for using the same model that further provides a quantitative criterion for the crossover between the two regimes.