An LBM-PNM framework for immiscible flow: With applications to droplet spreading on porous surfaces

Four-petal aqueous imbibition into woven cloth

HYPOTHESIS

Improving the processing efficiency of aerosol-coating technologies during mass production requires optimal nozzle spacing to allow complete surface coverage while at the same time not over-using the coating fluid. The difficult challenge is to estimate quantitatively the substrate coverage of fine droplets. Bouncing, splashing, and imbibition of droplets on solid surfaces have been widely explored, but little attention has been paid to liquid imbibition into woven textiles.

EXPERIMENTS

Here, we experimentally and theoretically study the imbibition dynamics of aqueous droplets on woven cloths. The experimental process was observed using magnified visual observation. A proposed continuum mathematical model well predicts the aqueous imbibition fronts as a function of time.

FINDINGS

A captivating four-petal imbibition spreading pattern is observed at enhanced magnification. The imbibition occurs separately in the megapores of the cloth between yarns, and in smaller minipores within individual yarn bundles. Surprisingly, weave intersections do not allow cross imbibition accentuating an anisotropic imbibition pattern. The proposed model achieves quantitative agreement with experiment. This is the first time that the mechanisms of four-petal droplet deposition, spreading, and imbibition into woven cloth have been outlined and successfully simulated. The mathematical model predicts advancement of liquids in anisotropic woven cloth, and permits evaluation of the coverages of droplet spreading.

Lattice Boltzmann Modeling of a Sessile and a Body Force-Driven Sliding Droplet over a Grooved Surface

This work presents the numerical modeling of a droplet’s sessile and dynamic behavior on a grooved surface. A droplet is placed on horizontal and vertical sliding conditions to observe its behavior under wettable and non-wettable conditions. The numerical analysis uses the multicomponent multiphase Shan-Chen Lattice Boltzmann Model (SC-LBM). The Cassie–Baxter and Wenzel states are reproduced for the sessile condition, and the enhancement of the contact angle is appreciated under the action of the grooved-ridged horizontal surface. The sliding droplet is analyzed through the Bond number by varying the ratio between the body force and the surface tension number. For Cassie–Baxter and Wenzel wettability conditions, a critical Bond number was discovered above which the sliding droplet will continue to deform indefinitely. The numerical model proved its suitability to predict the gradual deformation of a droplet over a grooved vertical surface subject to a tangential body force until the droplet eventually reaches a sessile condition or a breakup.

Rupture of Liquid Bridges on Porous Tips: Competing Mechanisms of Spontaneous Imbibition and Stretching

Liquid bridges are commonly encountered in nature and the liquid transfer induced by their rupture is widely used in various industrial applications. In this work, with the focus on the porous tip, we studied the impacts of capillary effects on the liquid transfer induced by the rupture through numerical simulations. To depict the capillary effects of a porous tip, a time scale ratio, R_T, is proposed to compare the competing mechanisms of spontaneous imbibition and external drag. In terms of R_T, we then develop a theoretical model for estimating the liquid retention ratio considering the geometry, porosity, and wettability of tips. The mechanism presented in this work provides a possible approach to control the liquid transfer with better accuracy in microfluidics or microfabrications.