Flows In Porous Domains Research Articles

Pore-scale effects during the transition from capillary- to viscosity-dominated flow dynamics within microfluidic porous-like domains

We perform a numerical and experimental study of immiscible two-phase flows within predominantly 2D transparent PDMS microfluidic domains with disordered pillar-like obstacles, that effectively serve as artificial porous structures. Using a high sensitivity pressure sensor at the flow inlet, we capture experimentally the pressure dynamics under fixed flow rate conditions as the fluid–fluid interface advances within the porous domain, while also monitoring the corresponding phase distribution patterns using optical microscopy. Our experimental study covers 4 orders of magnitude with respect to the injection flow rate and highlights the characteristics of immiscible displacement processes during the transition from the capillarity-controlled interface displacement regime at lower flow rates, where the pores are invaded sequentially in the form of Haines jumps, to the viscosity-dominated regime, where multiple pores are invaded simultaneously. In the capillary regime, we recover a clear correlation between the recorded inlet pressure and the pore-throat diameter invaded by the interface that follows the Young–Laplace equation, while during the transition to the viscous regime such a correlation is no longer evident due to multiple pore-throats being invaded simultaneously (but also due to significant viscous pressure drop along the inlet and outlet channels, that effectively mask capillary effects). The performed experimental study serves for the validation of a robust Level-Set model capable of explicitly tracking interfacial dynamics at sub-pore scale resolutions under identical flow conditions. The numerical model is validated against both well-established theoretical flow models, that account for the effects of viscous and capillary forces on interfacial dynamics, and the experimental results obtained using the developed microfluidic setup over a wide range of capillary numbers. Our results show that the proposed numerical model recovers very well the experimentally observed flow dynamics in terms of phase distribution patterns and inlet pressures, but also the effects of viscous flow on the apparent (i.e. dynamic) contact angles in the vicinity of the pore walls. For the first time in the literature, this work clearly shows that the proposed numerical approach has an undoubtable strong potential to simulate multiphase flow in porous domains over a wide range of Capillary numbers.

Simulation of incompressible flows in channels containing fluid and porous regions

Flows and heat transfer in channels containing both fluid and porous regions play an important role in various engineering applications. A better understanding of fundamental mechanisms in the fluid flows in porous regions are required in order to design and optimise gas bearings, air filters, and thermal insulation in the specific applications. Darcy-Brinkman-Forchheimer model is used to describe the flow inside the porous domain. The finite volume method is applied to solve these equations in a porous and open domain. The capabilities of the mathematical model and computational algorithm are demonstrated using test cases from various areas of practical applications. The effect of various physical quantities on velocity and pressure distributions is studied. The results of the numerical simulation of flows in porous domains are presented. The results obtained are in a good agreement with the experimental and numerical data available in the literature.

Simulation of incompressible flows in channels containing fluid and porous regions

Flows and heat transfer in channels containing both fluid and porous regions play an important role in various engineering applications. A better understanding of fundamental mechanisms in the fluid flows in porous regions are required in order to design and optimise gas bearings, air filters, and thermal insulation in the specific applications. Darcy-Brinkman-Forchheimer model is used to describe the flow inside the porous domain. The finite volume method is applied to solve these equations in a porous and open domain. The capabilities of the mathematical model and computational algorithm are demonstrated using test cases from various areas of practical applications. The effect of various physical quantities on velocity and pressure distributions is studied. The results of the numerical simulation of flows in porous domains are presented. The results obtained are in a good agreement with the experimental and numerical data available in the literature.

Diffusion and Flow in Porous Domains Constructed Using Process-Based and Stochastic Techniques

Two model mesoporous materials, namely Vycor glass and alumina membrane made by compaction of spherical monosize alumina particles, are reconstructed and the transport properties (Knudsen diffusivity, molecular diffusivity and permeability) of the resulting 3-dimensional binary domains are investigated through computer simulations. For the alumina membrane, two reconstruction alternatives are used, a ballistic deposition of spherical particles (process-based approach) and a stochastic procedure based on the porosity and the two-point correlation function of the porous matrix. For Vycor glass, only the stochastic reconstruction technique is employed. The obtained 3-D samples are structurally characterized in terms of their two-point correlation and chord length distribution functions. This type of information along with the comparisons between computed and reported transport coefficients indicate that the random sphere pack obtained from the ballistic-deposition procedure represents quite well the porous structure of the alumina membrane while the stochastically reconstructed domain fails to do so. In contrast, for the Vycor glass it is shown that the stochastic reconstruction technique is sufficient for a faithful representation of the porous matrix. It is furthermore argued that in the case of Vycor the stochastic reconstruction technique constitutes a kind of process-based approach.