Method of determining the cohesion and adhesion parameters in the Shan-Chen multicomponent multiphase lattice Boltzmann models

This work focuses on the simulation and experimental study of directional wicking of water on a surface structured by open microchannels. Stainless steel was chosen as the material for the structure motivated by industrial applications as fuel cells. Inspired by nature and literature, we designed a fin type structure. Using Selective Laser Melting (SLM) the fin type structure was manufactured additively with a resolution down to about 30 μm. The geometry was manufactured with three different scalings and both the experiments and the simulation show that the efficiency of the water transport depends on dimensionless numbers such as Reynolds and Capillary numbers. Full 3D numerical simulations of the multiphase Navier-Stokes equations using Volume of Fluid (VOF) and Lattice-Boltzmann (LBM) methods reproduce qualitatively the experimental results and provide new insight into the details of dynamics at small space and time scales. The influence of the static contact angle on the directional wicking was also studied. The simulation enabled estimation of the contact angle threshold beyond which transport vanishes in addition to the optimal contact angle for transport.

https://www.mdpi.com/1996-1944/14/3/490/pdf

Directional Water Wicking on a Metal Surface Patterned by Microchannels.

To investigate droplet formation in a microchannel with different walls, simulations were conducted based on a pseudopotential model using the exact difference method force scheme. The variable surface tension was obtained using Laplace’s law, and the static contact angle was estimated using a first-order linear equation of the corresponding control parameter of the model. The droplet motion in microchannels was simulated using our model, and the effects of surface wettability and the Bond number on the droplet motion were investigated. The droplet motion for the intermediate microchannel wall took a significantly shorter time than that for the hydrophilic wall, and the wet length also depended on the contact angle. As the Bond number increased, the wet length of the droplet decreased on the hydrophilic surface. The droplet formation in a T-junction device was also simulated using the proposed model, and the effects of the capillary number and viscosity ratio on droplet formation were discussed in detail, and some empirical correlations between the capillary number and dimensionless droplet length are presented according to different viscosity ratios. The three flow patterns of droplet formation were categorized by the different capillary numbers as the dripping–squeezing, jetting–shearing, and threading regimes. In the dripping–squeezing regime, the droplet volume was nearly independent of the viscosity ratio, but the viscous effect was more prone to occur in the jetting–shearing regime. In the jetting–shearing regime, as the capillary number increased, the effect of the viscosity ratio on droplet formation became more significant. 

Pseudopotential Lattice Boltzmann Model for Immiscible Multicomponent Flows in Microchannels

Directional and self-propelled flow in open channels has a variety of applications, including microfluidic and medical devices, industrial filtration processes, fog-harvesting, and condensing apparatuses. Here, we present versatile three-dimensional-printed liquid diodes that enable spontaneous unidirectional flow over long distances for a wide range of liquid contact angles (CAs). Typically, we can achieve average flow velocities of several millimeters per second over a distance of tens to hundreds millimeters. The diodes have two key design principles. First, a sudden widening in the channels' width, in combination with a small bump, the pitch, ensure pinning of the liquid in the backward direction. Second, an adjustable reservoir with differing expansion angles, the bulga, is introduced to manipulate the liquid velocity. Using a combination of experiments and lattice Boltzmann simulations, we provide a comprehensive analysis of the flow behavior and speed within the channels depending on CAs, pitch heights, and bulga angles. This provides guidelines for the fabrication of bespoke liquid diodes with optimal design for their potential applications. As a feasibility investigation, we test our design for condensation of water from fog and subsequent transport uphill.

https://aip.scitation.org/doi/pdf/10.1063/5.0122281

Three-dimensional printed liquid diodes with tunable velocity: Design guidelines and applications for liquid collection and transport

Numerical study of drop behavior in a pore space

This thesis is part of a wider project that aims at improving proton exchange membrane fuel cell (PEMFC) eﬃciency and stability. Our contribution aims at improving the geometry and structure of channels in anode and cathode bipolar plates (BPP) using experiments and simulations. The operation of a PEMFC involves multiphase ﬂows and multiphysics phenomenon such as reactant concentration and electron exchange between the components. To simulate such a complex system employed industrial codes as well as Lattice Boltzmann Method. Chapter 1 reminds the basic principle of PEM fuel cell and the role of the ﬂuids that ﬂow through BPP channels. We describe a standard version of the latter and the modiﬁcations which we consider here. Chapter 2 details a classical model that describes PEM fuel cell operation in steady regime and assumes single phase ﬂows in channels. The underlying equations and their simulation (using COMSOL) are validated by an experiment performed on standard single cell. The simulation evidences channels exhibiting unequal ﬂuid ﬂuxes while the literature points the negative eﬀects of such heterogeneity. Since the used models disregards the possibility of having water in two phases, Chapter 3 describes a LBMcolorgradientcodefortwophaseﬂows. Wevalidateitagainstanexperimentperformed of a T-junction, a device that has applications beyond fuel cell. Chapter 4, diﬀerently, is devoted to steady gas ﬂows in parallel channels that diﬀer from standard fuel cell. An algorithm automatically homogenizes the ﬂuid ﬂow by modifying domain geometry within deﬁnite limits. It applies to diverse settings, and manages parallel channels by varying parameters as channel number and widths. However, the distributing channels that span the ﬂuid between channels at BPP inlet and recollect it at outlet also matter. The author thus proposes designs that equalize channel ﬂows. The author creates a new design to study the manufacturing feasibility of BPP. Chapter 5 describes water drop directional spreading on metallic structures decorated with ﬁn shaped channels of parallel axis: experiments reveal almost total spreading only in one direction. Three dimensional LBM and Volume of Fluid simulationsretrievetheobservedtrendandcapturesmallerscaledetailssuggestingsubsetsof the ﬂuid domain where capillary forces or inertia dominate. Most signiﬁcant results are two phase ﬂows simulations. They describe the diﬀerent regimes of ﬁlms or drops at the outlet of a T-junction whose other branches are fed with immiscible wetting and non-wetting ﬂuids. Moreover, they describe how water drops spread on a microscopic relief which results into skewed capillary force.

Numerical and Experimental Approach for Bipolar Plates in PEM Fuel Cells : Novel Designs of Fluid Domain

Liquid film or drop wicking on solid surface without any external energy input is highly desirable in specific industrial processes. This paper proposes a numerical study of the dynamics of liquid wicking on geometrically structured flat surface. We consider structures deduced from flat surface by super-imposing a series of identical parallel channels, the ensemble being made of the same material. Channels exhibit arrow-shaped patterns. We analyse drop wicking on such a structure using numerical simulation and experiment. Both approaches reveal non symmetric wicking clearly exhibiting a privileged direction. The simulation captures the evolution of the liquid/air interface at smaller time scales and reveals wicking with rapid pulses suggested by the experiment.

/pdf/geometrically-driven-liquid-wicking-numerical-study-and-277quh9g1p.pdf

Geometrically driven liquid wicking: numerical study and experimental validation

We investigate the interaction of two immiscible fluids in a head-on device geometry, where both fluids are streaming opposite to each other. The simulations are based on the two-dimensional (2D) lattice Boltzmann method (LBM) using the Rothman and Keller (RK) model. We validate the LBM code with several benchmarks such as the bubble test, static contact angle, and layered flow. For the first time, we simulate a head-on device by forcing periodicity and a volume force to induce the flow. From low to high flow rates, three main flow patterns are observed in the head-on device, which are dripping-squeezing, jetting-shearing, and threading. In the squeezing regime, the flow is steady and the droplets are equal. The jetting-shearing flow is not as stable as dripping-squeezing. Moreover, the formation of droplets is shifted downstream into the main channel. The last flow form is threading, in which the immiscible fluids flow parallel downstream to the outlet. In contrast to other studies, we select larger microfluidic channels with 1-mm channel width to achieve relatively high volumetric fluxes as used in chemical synthesis reactors. Consequently, the capillary number of the flow regimes is smaller than 10−5. In conclusion, the simulation compares well to experimental data.

/pdf/lattice-boltzmann-simulation-and-experimental-validation-of-2n3niyyt1j.pdf

Lattice-Boltzmann Simulation and Experimental Validation of a Microfluidic T-Junction for Slug Flow Generation

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Papers

Directional Water Wicking on a Metal Surface Patterned by Microchannels.

Numerical and Experimental Approach for Bipolar Plates in PEM Fuel Cells : Novel Designs of Fluid Domain

Geometrically driven liquid wicking: numerical study and experimental validation

Lattice-Boltzmann Simulation and Experimental Validation of a Microfluidic T-Junction for Slug Flow Generation