Transport in Porous Media最新文献

This study investigates the use of X-ray microtomography (XMT) to reveal the structure of complex porous biological tissues and the fluid flow through them during wetting. It also evaluates fluid dynamical simulations based on XMT data to reproduce and analyse these flows, with a final aim of revealing fluid transport and void formation in such tissues. To fulfil the objectives, the wetting flow of a polymer liquid through an initially dry conditioned Norway spruce wood sample is visualised using XMT at the MAX IV synchrotron. The liquid flow front progression captured after 24 s and 48 s reveals uneven filling of longitudinal tracheids and flow between them via the tiny pits which connect tracheids. Most tracheids fill between 24 and 48 s, possibly due to removal of air inclusions. Large density gradients near cell walls suggest that the fluid followed and deposited along wall structures. Computational fluid dynamics simulations (CFD) of saturated flow through the tomography-based geometry indicate velocity profiles that resemble pipe flow in longitudinal tracheids and flow rate differences among them. The latter indicates that the geometry itself may cause the experimentally observed uneven flow. Streamlines show intra-tracheid flow development and clear flow direction change at the pits. Additionally, wetting simulations, using a constant contact angle, capture initial uneven filling between the tracheids on shorter time scales than could be capture by the experiments. These simulations furthermore show air entrapment during filling, consistent with experimental observations. Combining XMT with CFD enables detailed studies of flow in biological porous media. Faster X-ray scanning, incorporating dynamic contact angles and accounting for diffusion in simulations could further refine insights into fluid progression during capillary-driven flow into complex structures of porous biological tissues.

Sequestering carbon dioxide ((hbox {CO}_2)) in deep-ocean sediments is deemed as a promising approach to reducing carbon emissions. Under the low-temperature high-pressure condition of deep-ocean sediments, there may exist hydrate formation zone (HFZ) where solid (hbox {CO}_2) hydrate forms and negative buoyancy zone (NBZ) where (hbox {CO}_2) is denser than water. Both of the HFZ and the NBZ suppress the upward movement of the (hbox {CO}_2) plume; therefore, permanent storage was proposed in the deep-ocean sediment even if there is no low-permeability caprock on the top of the reservoir. However, in virtue of numerical simulations on (hbox {CO}_2) injection over a wide range of deep-ocean sediment conditions, we find that neither the HFZ, the NBZ nor the combination of the HFZ and NBZ makes sufficient condition for permanent (hbox {CO}_2) storage in the deep-ocean sediment, and we cannot evaluate the (hbox {CO}_2) storage security simply based on the existence of the HFZ and the NBZ. This is because (1) only a very small amount of hydrate forms in the HFZ and the formed hydrate may dissociate with continuous (hbox {CO}_2) injection and (2) the negative gravitation trapping by the NBZ may fail if the permeability of the sediment is not high enough to make the negative buoyancy force effective. We also find that the NBZ may shrink because the temperature increase due to exothermic hydrate formation may significantly reduce (hbox {CO}_2) density and we propose a new method to calculate the size of the NBZ. Finally, unconditional permanent (hbox {CO}_2) storage may only exist in high-permeability sediments with NBZ.

Structure and dynamics of turbulent open channel flow over permeable and impermeable sediment beds are investigated using pore-resolved, direct numerical simulations. Time-space double-averaged statistics are computed in four configurations: (i) permeable bed with randomly packed sediment grains, (ii) an impermeable wall with full layer of roughness elements matching the top layer of the sediment bed, (iii) an impermeable wall with half layer of roughness elements, and (iv) a smooth wall. It is observed that the mean velocity, Reynolds stresses, and form-induced pressure–velocity correlations representing ejection and sweep fluxes are similar in magnitude for the permeable-bed and impermeable full-layer cases. The wall-blocking effect present in the impermeable half layer results in higher streamwise and lower wall-normal stresses compared to the permeable bed. Bed roughness increases Reynolds shear stress, whereas permeability has minimal influence. However, bed permeability significantly influences form-induced shear stress. Pressure fluctuations and volume-averaged bed-normal distribution of the drag force peak in the top layer of the bed. These findings suggest that reach-scale transport in the hyporheic zone will be better captured by providing boundary conditions based on stream flow simulations that incorporate the roughness effect of the top layer of the bed.

This study investigates the impact of fin parameters on natural convection heat transfer in the closed cavity with a heat source. The analysis focuses on the comparison of the thermal performance between solid and porous fins. Firstly, the influence of individual parameter changes is analyzed. Based on these findings, the response surface optimization method is applied to explore the heat transfer characteristics when multiple fin parameters vary simultaneously. The results of single parameter variation show that the installation angle of porous fins has the most significant influence on the average Nusselt number of the heat source surface. For solid fins, the fin length has the greatest impact. The interaction between the installation angle and the length of the porous fin has the most significant effect on the average Nusselt number of the heat source surface, reaching a maximum value of 11.65. Compared to the cavity without fins, the optimal configuration enhances the average Nusselt number by 12.02%. The corresponding optimal parameters for the porous fin are θ = 118.3°, l = 0.288H and a = 0.664H. Similarly, for the solid fin, the interaction between the installation angle and fin length has the most significant effect on the average Nusselt number of the heat source surface. Correspondingly, the maximum average Nusselt number on the surface of the heat source reaches 11.57, representing an 11.32% increase compared to the cavity without fins. The optimal parameters for the solid fin are θ = 108.9°, l = 0.021H, a = 0.747H.

In this study, we analyze combustion waves in a simplified one-dimensional model for porous media, focusing on the case of backward propagating combustion where the combustion front moves opposite to the direction of the injected airflow, resulting in negative wave velocity. The mathematical model consists of three coupled partial differential equations governing temperature, oxygen, and fuel concentrations. Assuming that oxygen is transported faster than heat, we reduce the system to a form suitable for phase plane analysis and establish the existence of counterflow traveling wave solutions. Our work extends previous results on coflow combustion waves by providing a comprehensive classification of counterflow wave types and their properties. The existence and structure of these waves are rigorously demonstrated through dynamical systems techniques, offering new insights into the behavior of combustion fronts in porous media.

In this work, the modelling of entropy generation on heat transport of natural convection of an electrically conducting Walters’ B fluid is examined. The flow through a porous medium radiates nonlinearly in the presence of viscous dissipation and Joule heating. Subject to the suitable dimensionless variables, the coupled nonlinear dimensional equations are transformed into ordinary differential equations via a similarity variable and executed by Galerkin Weighted Residual Method (GWRM). The results obtained demonstrated good agreement with another method when validated by Spectral Collocation Method (SCM) through tables, as well as numerical integration of Mathematica’s NDSolve for the graphs. The dynamics of the embedded parameters are presented through graphs. Keeping in mind the engineering applications of the study, the Skin-friction and Nusselt number results are conveyed through tables. The result justified, among other important findings, that temperature distribution cools over the higher dominance of buoyancy force over the viscous force, which is a useful tool in application for cooling of the system. The interaction of the Brinkman number intensifies viscous heating due to the heat transfer by virtue of the molecular conduction around the system. The outcome of this process improves entropy production in applications.

In this paper, we study the Forchheimer-extended Darcy–Brinkman–Boussinesq fluid flow through a thin channel filled with porous medium using methods of asymptotic analysis. The fluid inside the channel is cooled (or heated) by the surrounding medium, and the flow is governed by the prescribed pressure drop between the pipe’s ends. Employing asymptotic analysis with respect to the small parameter representing the channel’s thickness, we derive a first-order asymptotic approximation for the velocity, pressure and temperature. The velocity approximation explicitly acknowledges the thermal effects as well as the inertial effects. These effects are clearly visualized in the provided numerical examples. Finally, we rigorously justify the obtained asymptotic model via the error estimates in suitable norms in order to indicate the order of accuracy of the proposed approximate solution.

Wettability, as represented by contact angles, impacts the multifluid configuration inside porous media, which determines the media’s upscaled behavior. An accurate description of the wettability is therefore crucial in determining and understanding macroscopic flow behavior, such as relative permeability and capillary pressure. Traditional experimental and numerical studies determine the aggregate wettability of a medium as a single parameter assigned to the whole sample. However, the wettability could vary spatially throughout the domain. Advances in micro-CT scanning have improved the capability to see the solid and fluid distribution inside porous media. This has led to more recent developments of different numerical methods to determine the wettability distribution based on segmented micro-CT images. This paper reviews different numerical methods for wettability characterization on three-dimensional (3D) pore-scale images of fluid distribution, concerning their methodology, accuracy, and computational cost where applicable. This study tries to cover all numerical methods for characterizing wettability distribution based on the segmented micro-CT images as of the time of this manuscript. We have divided the methods into six categories: geometry-, topology-, multiphase-, machine learning-, thermodynamic-, and event-based methods. Developments within each category are reviewed, and the different categories are compared. While no category stands out, as they all have different strengths and weaknesses, the geometry-based method tends to be most versatile and robust.

This article focuses on single phase compressible gas flow in porous media, especially hydrogen (H_2) or other gases like air. It includes a comprehensive literature review on analytical approaches to gas flow, Klinkenberg effect, and other effects like gravitational acceleration (super-gravity cases). The review investigates previous findings for ideal gas flow under isothermal conditions under various conditions – including one-dimensional (1D) permeametric flow conditions – taking into account perfect gas compressibility and the Klinkenberg effect due to gas slippage in fine pores. Usually, gravitational acceleration is neglected in the gas flow literature: this classical assumption is assessed quantitatively, and a new 1D analytical solution is developed at steady state for the case of strong gravitational acceleration, as may arise under centrifugal conditions. On the other hand, new 1D analytical solutions are developed for space-time gas pressure profiles and for mass flux density profiles in the porous column, with or without Klinkenberg effect. These analytical solutions are tested and compared to numerical simulations, both Finite Volume and Finite Element. Both the gas pressure profiles and the mass flux density profiles approach the exact steady state at large times. Furthermore, it is is demonstrated that the proposed analytical solution for gas pressure is a fair approximation over a broad range of time scales, from early times up to large times approaching steady state.