Transport in Porous Media最新文献

In this study, we present a successful application of the Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) for simulating the complex phenomenon of multi-particle arch formation within high-concentration packed-bed environments. We investigate the roles of physical forces in this phenomenon, shedding light on aspects that are challenging to explore through experimentation. Our research is motivated by the desire to comprehend the conditions and parameters influencing the formation, stability, disruption, and reformation of multi-particle sand arches within filter openings. This arching phenomenon serves as an efficient particle retention mechanism, particularly in heavy oil production wells. We delve into factors like particle size, shape, and particle size distribution that may impact multi-particle arch performance. Additionally, we explore the physics behind multi-particle arching by examining the effects of various physical forces on arch performance. Utilizing a Computational Fluid Dynamics–Discrete Element Model, we investigate the multi-particle arching phenomenon under steady-state flow conditions in packed-bed environments. Our approach employs the unresolved coupling method in STAR-CCM+ (Siemens PLM). We test various filter slot geometries, including straight slots, keystone slots, wire-wrapped screens (WWS), and seamed slots, all under laminar flow conditions. Our findings highlight the significance of gravity, inter-particle forces, and interactions between the filter wall and the particles in multi-particle arch formation at both the slot opening and microscale levels. We confirm that a multi-particle arch can be formed within a specific slot width. Interestingly, while maintaining a constant slot width, we observe that the slot length has an insignificant effect on multi-particle arch formation and stability. In summary, our CFD–DEM model successfully simulates and predicts multi-particle arch formation, stabilization, breakage, and reformation, allowing for comprehensive testing of the effects of various parameters. This research offers valuable insights into a complex phenomenon that is crucial in packed-bed filtration systems.

The co-moving velocity is a new variable in the description of immiscible two-phase flow in porous media. It is the saturation-weighted average over the derivatives of the seepage velocities of the two immiscible fluids with respect to saturation. Based on analysis of relative permeability data and computational modeling, it has been proposed that the co-moving velocity is linear when plotted against the derivative of the average seepage velocity with respect to the saturation, the flow derivative. I show here that it is enough to demand that the co-moving velocity is characterized by an additive parameter in addition to the flow derivative to be linear. This has profound consequences for relative permeability theory as it leads to a differential equation relating the two relative permeabilities describing the flow. I present this equation together with two solutions.

We consider a cross-sectional study of immiscible displacement under the influence of gravity, anisotropic permeability, and capillary effects. We propose the similarity criteria characterizing the relative role of these effects and qualitatively different flows. We present a classification of the flow regimes in four limiting cases of the displacement. The recovery and sweep efficiencies in such cases can be compromised by the gravity override, channeling, and coning effects. In the phase plane, we constrain the parameter ranges at which these effects become relevant. We then aim at evaluating the range of the similarity criteria characterized by the maximum efficiencies and describe the placements of horizontal wells allowing to reach these maxima. We show that the placement of the producing well is generally more relevant. In the limiting cases, the variety of placements can be merged in groups by their efficiencies. We eventually come up with the maps of the maximal efficiencies and associated placements allowing for a quick assessment of the optimal injection scenarios. The proposed classification of the flow regimes and the calculated maps can be useful in evaluating various scenarios of waterflooding and gas injection.

The rate of oxygen diffusion directly affects the distribution of oxygen concentration within concrete, which in turn influences the corrosion performance of reinforcing steel within the concrete. However, research on cross-scale prediction models for oxygen diffusion in dry concrete is still lacking. In this study, the complex pore structure of concrete is simplified into a sponge model, and three types of diffusion are quantitatively characterized based on the pore size distribution density function. The influence of porosity, water–cement ratio, hydration degree, gel–space ratio and pore tortuosity on the oxygen diffusion coefficient is considered, and a cross-scale prediction model for oxygen diffusion in dry concrete is established. Secondly, an oxygen diffusion coefficient determination device developed independently is used to measure the oxygen diffusion coefficient of concrete specimens under dry conditions. The results show that the experimental values agree well with the calculated values, and the model is compared with other models proposed by scholars, verifying its superiority and accuracy. Finally, a parameter sensitivity analysis is conducted on five microscale parameters and their influence on the behavior of oxygen transmission into concrete is discussed. The establishment of the cross-scale prediction model for oxygen diffusion in dry concrete will first provide a positive role in the theoretical research on reinforcement expansion and cracking, and secondly, it will be able to better explain the mechanism of oxygen diffusion in concrete.

Determining the (in)efficiency of wetting phase displacement by an invading non-wetting phase (drainage) in a single fracture is key to modelling upscaled properties such as relative permeability and capillary pressure. These constitutive relationships are fundamental to quantifying the contribution, or lack thereof, of conductive fracture systems to long-term leakage rates. Single-fracture-scale modelling and experimental studies have investigated this process, however, a lack of visualization of drainage in a truly representative sample at sufficient spatial and temporal resolution limits their predictive insights. Here, we used fast synchrotron X-ray tomography to image drainage in a natural geological fracture by capturing consecutive 2.75 μm voxel images with a 1 s scan time. Drainage was conducted under capillary-dominated conditions, where percolation-type patterns are expected. We observe this continuously connected invasion (capillary fingering) only to be valid in local regions with relative roughness, λ_b ≤ 0.56. Fractal dimension analysis of these invasion patterns strongly aligns with capillary fingering patterns previously reported in low λ_b fractures and porous media. Connected invasion is prevented from being the dominant invasion mechanism globally due to high aperture heterogeneity, where we observe disconnected invasion (snap-off, fragmented clusters) to be pervasive in local regions where λ_b ≥ 0.67. Our results indicate that relative roughness has significant control on flow as it influences fluid conductivity and thus provides an important metric to predict invasion dynamics during slow drainage.

This study investigates multiphase flow with non-Newtonian fluid at pore scale, using the Compressive Continuum Species Transfer (C-CST) method in a microchannel and 2D porous media, with emphasis on drainage and mass transfer between fluids through the Volume of Fluid (VOF) method. The object of study is the multiphase flow in oil reservoirs, where immiscible fluids coexist in the porous media. The use of recovery methods becomes relevant in scenarios of low reservoir energy or when the physical properties of the oil compromise the flow. The influence of petroleum rheology, especially heavy crude oil with non-Newtonian viscoelastic behaviour, is considered. Recovery methods, such as the injection of CO₂, aim to optimize the flow by modifying the rheological properties of the fluid. This article aims to conduct a numerical analysis using the C-CST method with Direct Numerical Simulation (DNS) and volume tracking techniques to capture an interface between fluids. The main objective is to numerically implement a non-Newtonian rheological model in the linear momentum conservation equation, comparing the flow between non-Newtonian and Newtonian fluids at pore scale, and analysing the mass transfer at the flow interface with this new approach.

Understanding the dynamics of the filling process of a pore body with a nonwetting fluid is important in the context of dynamic pore network models and others. It can justify many of the assumptions behind the different rules that describe how the network behaves during imbibition and drainage processes. It also provides insight into the different regimes pertinent to this system. The filling process starts with the contact line pinning at the pore entrance. Three regimes can be identified during the filling process that is related to how the contact line advances. In the first two regimes, the contact line pins at the pore entrance while the emerging droplet develops, and in the third one, the contact line departs the entrance of the pore and advances along the pore surface. During the first regime, which is brief, the curvature of the meniscus increases, and likewise, the corresponding capillary pressure, while in the other two regimes, the curvature decreases and so does the capillary pressure. Such behavior results in the rate at which the nonwetting fluid invades the pore to change. It initially decreases, then increases as the meniscus advances. The radius of curvature of the meniscus, eventually, increases to infinity for which the interface assumes a flat configuration. A one-dimensional modeling approach is developed that accounts for all these regimes. The model also considers the two immiscible fluids over a wide spectrum of contrast in viscosity. Information about the mean velocity of the invading fluid, the location of the contact line, the radius of curvature of the meniscus, the volume of the emerging droplet, and several others are among the details that the model provides. A computational fluid dynamics (CFD) simulation has also been considered to confirm the proposed fates of the interface and to provide a framework for comparisons. The results of the validation process show, generally, a very good match between the model and the CFD analysis.

We review models for unsteady porous media flow in the volume-averaging framework and we discuss the theoretical relations between the models and the definition of the model coefficients (and the uncertainty therein). The different models are compared against direct numerical simulations of oscillatory flow through a hexagonal sphere pack. The model constants are determined based on their definition in terms of the Stokes flow, the potential flow and steady nonlinear flow. Thus, the discrepancies between the model predictions and the simulation data can be attributed to shortcomings of the models’ parametrisation. We found that an extension of the dynamic permeability model of Pride et al. (PRB 47(9):4964–4978, 1993) with a Forchheimer-type nonlinearity performs very well for linear flow and for nonlinear flow at low and medium frequencies, but the Forchheimer term with a coefficient obtained from the steady-state overpredicts the nonlinear drag at high frequencies. The model reduces to the unsteady Forchheimer equation with an acceleration coefficient based on the static viscous tortuosity for low frequencies. The unsteady Forchheimer equation with an acceleration coefficient based on the high-frequency limit of the dynamic tortuosity has large errors for linear flow at medium and high frequencies, but low errors for nonlinear flow at all frequencies. This is explained by an error cancellation between the inertial and the nonlinear drag.

Porous ionic electrospray emitters have received significant interest for space propulsion due to their performance and operational simplicity. We have developed a diffusion equation for describing the transient flow response in a porous electrospray emitter, which allows for the prediction of the settling time for flow in the porous emitter. This equation accounts for both the change in liquid storage at exposed pores on the emitter with pressure and viscous diffusion through Darcy’s law. Transient flow solutions are provided for the most common emitter topologies: pillar, cone, and wedge. Transient flow solutions describe the settling time and magnitude of current overshoot from porous electrosprays, while providing useful guidelines for reducing transient response time through emitter design. Comparing diffusion of pressure to the onset delay model for electrospray emission shows that diffusion is most relevant at higher voltages and when a porous reservoir is used. Accounting for multiple emission sites on the wedge geometry shows that emission sites settle in proportion to emission site spacing to the power − 1.74.

This work conducts pore-scale numerical computations to reveal the hydrodynamic characteristics of the fully-developed flow through a fixed-bed reactor regularly packed with mono-sized spheres. One of the main purposes is to obtain invariant standard values which can be used as the benchmarks for those results from randomly packing methods such as Monte Carlo or DEM. Also, a repeatable and verifiable process is introduced to forecast the pressure drop and the mass flow rate in a packed bed without running any numerical simulation.

The mono-sized spheres in the present simulations are in FCC, BCC, or SC arrangement. For each packing, different Reynolds numbers and lattice angles are considered. For these regular arrangements, it is revealed that the cross-section of the reactor can be clearly separated into two regions: the more loosely-packed near-wall region and the densely-packed core region, with a boundary at a half-sphere diameter distance from the wall. The mass flow rates into the two regions will self-adjust themselves in proportion. Consequently, separate average Reynolds numbers in the near-wall, Re_w, and the core region, Re_co, are defined. Comparison of our computational results for fully-developed conditions with the experimental data for regular packings is presented. However, the inevitable presence of the entrance effect in the experiments on insufficiently-long regular packed beds forbids pertinent comparison. This work then continues to present a simplified model to predict the pressure drop through a reactor randomly packed with mono-sized spheres. The empirical correlations of C_D (times) d/L with Re_w or Re_co in respective regions are derived. These correlations can be used to evaluate the pressure drop through a reactor at a given total mass flow rate, which is proportioned in each region. A linear interpolation or extrapolation procedure is proposed to evaluate the (Delta) P based on the ((1/Delta) P_FCC)-({varepsilon }_{text{FCC}}), ((1/Delta Ptext{BCC}))-({varepsilon }_{text{BCC}}), and ((1/Delta) P_SC)-({varepsilon }_{text{SC}}) relations, with given average void fraction (varepsilon), diameter and length of the container, particle diameter, and total mass flow rate. The reliability of the simplified model has been validated through the comparison with empirical correlations and Monte Carlo simulation in the literature.