Mesoscale modelling of soft flowing crystals

Physical Review Fluids

We present a mesoscale representation of near-contact interactions between colliding droplets which permits one to reach up to the scale of full microfluidic devices, where such droplets are produced. The method is demonstrated for the case of colliding droplets and the formation of soft flowing crystals in flow-focusing microfluidic devices. This model may open up the possibility of multiscale simulation of microfluidic devices for the production of new droplet and bubble-based mesoscale porous materials.

arXiv (Cornell University), 2020

We provide a brief survey of our current developments in the simulation-based design of novel families of mesoscale porous materials using computational kinetic theory. Prospective applications on exascale computers are also briefly discussed and commented on, with reference to two specific examples of soft mesoscale materials: microfluid crystals and bi-continuous jels.

Physical Review Fluids

We propose a mesoscopic model of binary fluid mixtures with tunable viscosity ratio based on the two-range pseudo-potential lattice Boltzmann method, for the simulation of soft flowing systems. In addition to the short range repulsive interaction between species in the classical single-range model, a competing mechanism between the short range attractive and mid-range repulsive interactions is imposed within each species. Besides extending the range of attainable surface tension as compared with the single-range model, the proposed scheme is also shown to achieve a positive disjoining pressure, independently of the viscosity ratio. The latter property is crucial for many microfluidic applications involving a collection of disperse droplets with a different viscosity from the continuum phase. As a preliminary application, the relative effective viscosity of a pressure-driven emulsion in a planar channel is computed.

WIT Transactions on Engineering Sciences, 2008

Permeability is one of the most important bulk properties for the characterization of fluid flow in porous media. However, despite all the considerable body of research work over the past years using experimental, analytical, and numerical approaches, its determination is still a challenge. The methodologies, which have been used to measure, calculate and predict the permeability of different types of porous media, in general, tend to suffer from various levels of limitations in their applicability and, moreover, no general correlation for the permeability is available. Among the different predictive methods for the permeability, numerical pore level fluid flow analyses have been receiving increasing attention in the recent years, due to its robustness and flexibility. In this approach, the viscous fluid flow is directly simulated in the pores of the porous medium with no further modelling required. A simple representation of the pore structure can be in the form of the ordered and random packings of spheres, cylinders or square obstacles. In the present paper, the main objective is to introduce the lattice Boltzmann method (LBM) as a powerful tool for the mesoscopic pore level fluid flow simulation in porous media; two and three-dimensional case studies are presented to demonstrate the capabilities of the mesoscale modelling for porous media fluid flow problems using LBM. To demonstrate an approximation to a reconstructed medium, the fluid flow simulation in a 2D random arrangement of square obstacles with different aspect ratios is presented. Results of the three-dimensional simulations of the fluid flow in ordered packings of spheres are also reported; the results are in excellent agreement with the available analytical correlation for this configuration.

ECONTECHMOD : an international quarterly journal on economics of technology and modelling processes, 2015

Ab st r a ct. The mesoscale description of multiphase flow in a typical Lab-chip diagnostic device is presented in actual article. The mesoscopic lattice Boltzmann method, which involve evolution equations for the single particle distribution function, was applied for the modeling of complex microfluidic flows. The general D2Q9 lattice Boltzmann formulation, considered multiphase flows, was developed. Three types of boundary conditions were used for the mesoscopic modeling: "ghost-fluid", "bounce-back" and "periodic boundaries". Traditional Dirichlet and Neumann macroscopic boundary conditions were transformed into mesoscopic lattice formulations. Algorithm of fluid flow solution, based on BGK single-relaxation-time scheme was proposed and implemented. The scaling procedure was used for physical parameters convertion into non-dimensional units. Simulation procedure was tested on a fluid flow with single solid particle. The final results showed good consistence with fundamental flow phenomena. Ke y wo rd s: multiphase, microfluidics, flow, mesoscale, modeling.

Lab on a Chip, 2012

The objective of this study was to create a microfluidic model of complex porous media for studying single and multiphase flows. Most experimental porous media models consist of periodic geometries that lend themselves to comparison with well-developed theoretical predictions. However, many real porous media such as geological formations and biological tissues contain a degree of randomness and complexity at certain length scales that is not adequately represented in periodic geometries. To design an experimental tool to study these complex geometries, we created microfluidic models of random homogeneous and heterogeneous networks based on Voronoi tessellations. These networks consisted of approximately 600 grains separated by a highly connected network of channels with an overall porosity of 0.11-0.20. We found that introducing heterogeneities in the form of large cavities within the network changed the permeability in a way that cannot be predicted by the classical porositypermeability relationship known as the Kozeny equation. The values of permeability found in experiments were in excellent agreement with those calculated from three-dimensional lattice Boltzmann simulations. In two-phase flow experiments of oil displacement with water we found that the wettability of channel walls determined the pattern of water invasion, while the network topology determined the residual oil saturation. The presence of cavities increased the microscopic sweeping efficiency in water-oil displacement. These results suggest that complex network topologies lead to fluid flow behavior that is difficult to predict based solely on porosity. The novelty of this approach is a unique geometry generation algorithm coupled with microfabrication techniques to produce pore scale models of stochastic homogeneous and heterogeneous porous media. The ability to perform and visualize multiphase flow experiments within these geometries will be useful in measuring the mechanism(s) of displacement within micro-and nanoscale pores.

Chemical Engineering Science, 2003

A mesoscopic framework, derived from ÿrst principles via a rigorous coarse-graining of an underlying master equation, has proven to be a powerful tool in bridging the disparate scales between atomistic simulations and practical applications involving di usion of interacting species through microporous ÿlms. This mesoscopic framework is validated here via gradient continuous time Monte Carlo (G-CTMC) simulations for realistic boundary conditions in the limit of thin, single crystal membranes. It is shown that intermolecular forces have a non-Arrhenius e ect on the permeation ux, and a stationary concentration pattern develops for strong repulsive interactions. It is found that di usion through complex multiple site lattices, such as those encountered in di usion of benzene in Na-Y zeolite ÿlms, exhibits strongly nonlinear behavior even in the absence of interactions between molecular species. Finally, the mesoscopic framework is applied to di usion/reaction systems, where excellent agreement between G-CTMC and mesoscopic solutions is demonstrated for the ÿrst time. ?

Computational Materials Science, 2002

The importance of bridging length scales for materials is illustrated by three examples, nematic liquid crystals, strength of materials, and epitaxial growth. Emphasis is on the microscopic scale, with first-principles calculations of molecule-surface interaction, stacking-fault energies, interlayer interactions, diffusion barriers, and adsorbate-adsorbate interactions. Some pilot examples of using such information on the meso-and macroscales with models using director fields, misfit densities of dislocation, and monomer and island densities are presented. The area is predicted to have a great future. Ó

International Journal of Modern Physics C, 2007

We review some recent results in the theory of Lattice Boltzmann Equation applied in micro and nano channel flows. With a suitable generalization of the Shan-Chan model, we are able to relate in a systematic and self consistent way, the model parameters with the contact angle. Comparison with Molecular Dynamics simulations show remarkable agreement.

We have studied displacement mechanisms of immiscible fluids in micro-fluidic models with designs ranging from simple pore junctions to a pore from a rock thin section. For this purpose, we have developed a lattice-Boltzmann (LB) model to study the multi-phase flow processes in direct comparison with experimental results in purpose-built microfluidic geometries. In this paper, we will focus on the LB simulations, in direct comparison with the experiments. First, we study quasi-static drainage and imbibition processes in single junctions and observe good agreement with Young-Laplace capillary filling rules. However, for dynamic imbibition, we observe that the sequence of pore filling is determined by local pore geometry rather than the Young-Laplace law. The LB simulation results are in good agreement with the micro-fluidic experimental observations. Having validated the validity of the LB code for displacement mechanisms in single pores, we extend our calculations to multiple-pore displacement in pore space images of real rock samples obtained from micro-computed tomography (micro-CT) scans. We observe capillary pressure and relative permeability curves in good agreement with experiments.