Lattice Boltzmann Study Of The Droplet Dynamics In Porous Media

The multiphase flow through porous media is frequently encountered in the nature and a broad range of engineering applications, such as enhanced oil recovery, the devel-opment of fuel cell, the monitor and control of the ground water contamination, and so on, while the droplet dynamics in porous media is a key problem involved in those field-s. Although problems related have been studied profoundly, the multiphase flow transport in porous media is very complicated in general, such as the consideration of the forma-tion/coalescence/deformation/migration of the interface, and the interaction of between the fluid and solid walls, then, the physics mechanics behind this problem is not understand clearly. When study this kind of problem, the traditional computational fluid dynamics (CFD) methods will suffer from the complexity in boundary implementary, large amount of calculation, and low performance in parallel computing. The lattice Boltzmann method (Lattice Boltzmann Method, LBM) has been developed into a powerful tool for simulat-ing complex flow problems. It can conveniently describe the interactions between different phases due to the microscopic nature and mesoscopic characteristic, and it has been proven to have the distinct advantages over the conventional methods in simulating the multiphase flows.Up to now, studies on the droplet dynamics in porous media are few, and lots of fun-damental problems still demand systematic research, such as the consideration of the het-erogeneity of the porous media, deformation and breakup dynamics after passing the solid skeleton of the pore. Based on the engineering application background and the research status, the research work provides a numerical study on the droplet dynamics in porous me-dia by a lattice Boltzmann (LB) model for multiphase flows, aiming to reveal the flow and transport mechanisms, and specially study the following three related issues:(1) The dynamics of a droplet adhering to a rough surface in shear. The effects of the capillary number, surface wettability, the height and the space of the rough pillars on the droplet dynamics are analyzed. The major results are listed as follows, first, the capillary number and the wettability have significant effects on the deformation of the droplet, which becomes more pronounced with increasing capillary number; For the hydrophilic surface, the droplet can finally penetrate into the rough pillars, while for neutral and hydrophobic surfaces, the droplet could partially penetrate into the rough pillars. The critical capillary number (Cac) decreases with the increase of contact angle. Secondly, based on the dynamics of the contact line, we classify the droplet behavior into three different regimes:the attached droplet deforms with pinned contact lines, one end of the contact lines slips, and two ends of the droplet both slip. Note that the slip priorities of the contact lines between the cases of hydrophilic wetting and neutrally wetting are opposite. Finally, it is found that the height and the space of the rough pillars affect the wet length and penetration depth, in turn, leading to a different Cac.(2) The dynamics of a liquid droplet past a solid circular cylinder in microchannel. The effects of the eccentric ratio, viscosity ratio, surface wettability and Bond number on the droplet dynamic behavior are investigated. Numerical results show that, the eccentric ratio affects the passing patterns and the size ratio of the daughter dropleta, There is a critical eccentric ratio (βc) to decide the droplet can pass the cylinder with or without breakup. The viscosity ratio affects the breakup point, the shape/amount of the daughter drops, the depo-sition configuration, as well as the passing time tp. The wettability affects the distribution of the residual and βc.βc increases with the decrease of the θ, in other words, the droplet needs more space to completely pass the cylinder when the hydrophilicity increases. The Bond number (Bo) is closely related to tp and βc. tp decreases with the increase of the Bo number, while βc increases with the increase of the Bo number.(3) As a continuity of the above work, we further study the droplet pass two columns of solid cylinders as well as a cylinder-packed porous media, and our conclusions are listed as follows:For the first problem, it is found the viscosity ratio (λ) affects the break states:when λ>1, the droplet breaks into several tiny drops during the passing process. In contrary, the droplet will completely pass the gap between two columns of cylinders in a pattern of slender liquid column. The wettability affects the descending path:the high viscous and hydrophilic droplet descends along the longitudinal gap between cylinders. For low viscous drop, under the hydrophobic and hydrophilic conditions, both will descends along the horizontal gap. while the breakup and attachment phenomena occur in the latter case, increasing the difficulty of the displacement. The Bo number affects the passing velocity and breakup dynamics. When λ<1, the increase of Bo can speed up the passing process and enhance the breakup. While for λ<1, the effect of the Bo is not obvious. For the second problem, it is found that A affects the descending velocity and the max spreading length in the horizontal direction. For a same Bo, the descending length for high viscous droplet is larger than the low viscous droplet, and the variance of the spreading length is opposite. The wettability and Bo number determine whether the descending path is in an aggregated or dispersed state. The circular size and gap affect the spreading region and passing time in the porous media.In conclusion, we have adopted a lattice Boltzmann multiphase model to simulate the complex transport process of liquid droplet in porous media from the pore scale, mainly investigate the deformation and breakup dynamics of a droplet in shear, pass a single cylinder. Based on the researching results, we further study the droplet dynamics past several cylinder, analyze the parameter effects on the deformation, breakup and movements of the droplet, and also discover some new phenomena. This work can be viewed as a necessary basis for future studies and great insight into flow mechanisms of the droplet dynamics in porous media.