Porous Media Model Research Articles

Hydrodynamic Analysis of Flow Stabilization Process in a Miniature Circulating Water Channel Equipped with Combined Porous Plate Structures

As a foundational platform for fluid dynamics research on underwater devices, the quality of stable and uniform incoming flow in a circulating water channel (CWC) is essential. Due to the inherent structural characteristics of porous media, their application has become widespread in offshore and marine engineering. This study presents the design of a miniature circulating water channel, alongside the development of a computational fluid dynamics (CFD) numerical model to simulate the interaction between porous media and incoming flow. By analyzing the pressure loss of fluid within the porous plates and incorporating it as a source term in the momentum equation, heavy computational costs associated with fine mesh requirements in micro porous models were avoided. Simulations were conducted to investigate the effects of combined porous plates on the flow field, and the porous media model was validated by comparisons with experimental data. The distribution of the flow field within the channel was analyzed to define the test section, which was conducive to further structural optimization. The results indicated that the combined porous plates stabilized the flow field of the CWC, and, following structural optimization, the occurrence of backflow was reduced, thereby expanding the effective test section range.

Effect of pore plugging on transpiration cooling performance implemented with perforated flat plates

Transpiration cooling is expected to be one of the most effective cooling technologies for gas turbine blades. However, dust deposition can easily lead to pore plugging, which limits its practical application in engineering. The plugging of pores in conventional porous media models is difficult to predict, so it is essential to construct computational models with finely controllable porous structures. In this study, a transpiration cooling configuration with straight holes perforated with a diameter of 0.5 mm was adopted. The effects of plugging ratio and region on flow and heat transfer under different coolant injection ratios and pump power conditions were investigated by numerical simulation. The results showed that at constant mass flow rate, the overall cooling performance increased as the plugging ratio increased at low injection ratios. At high injection ratios, the opposite was true. With a certain pump power, as the plugging rate increased, the flow loss coefficient rose, leading to a decrease in cooling efficiency. Transpiration cooling efficiency was also highly sensitive to the distribution of plugged holes at the same plugging ratio. When the coolant flow was sufficient, the farther the plugged area was from the leading edge, the smaller the reduction in cooling efficiency.

A heat pipe calculation method based on the two-phase mixture model of porous medium

This paper proposes a new method for calculating heat pipes, in which the porous wick inside the heat pipe is described by the two-phase mixture model (TPMM) of porous medium based on the modified temperature model that adopts the local thermal equilibrium assumption. The capillary pressure inside the wick is characterized by the Leverett capillary pressure model. This model can calculate the two-phase flow within the heat pipe wick at the macroscopic scale level and achieves a full-field coupled solution for the wick-vapor-wall flow and heat transfer process by a specific coupling method. Finally, the paper conducts a coupled heat transfer calculation for a heat pipe using potassium as the working fluid, verifies the correctness of the model and solution method by comparing it with the experimental results, and studies the flow and phase transition patterns of the heat pipe under multiple heating and different overload conditions. Compared with the traditional single-phase porous medium model of heat pipes, the new model can consider phase transition within the porous wick. While compared with pore-scale methods, the macroscopic research scale of the new model can reduce the computational resources required.

Numerical study on wave propagating characteristics through an offshore pile-net enclosure structure

Large-scale pile-net enclosures are increasingly utilized in marine engineering. However, simulating their interactions with waves remains a significant challenge. This study presents a numerical model that coupled porous media model and direct-forcing immersed boundary method to simulate the interaction between the pile-net enclosure structure and waves. The damping effect of the netting was simulated by porous media, while the pile was simulated using the direct-forcing immersed boundary method. The numerical model was verified based on experimental results obtained from corresponding physical model tests. Using the proposed numerical approach, this paper investigates the effects of wave period, net solidity, spacings of piles and wave incident angles on the hydrodynamic of the pile-net enclosure structure, including wave field and pile group coefficients. The results show that the pile-net enclosure structure demonstrates a damping effect on wave propagation, particularly for high-frequency waves. An increase in net solidity significantly impacts the wave forces on downstream piles. Additionally, the angle of incidence of the wave affects the orientation of the reflected wave crest line. When the piles are symmetrically positioned in pairs along the wave propagation direction, the wave height inside the structure decreases.

3D thermodynamics and parameters analysis of the external combustion hot blast stove

The external combustion hot blast stove is widely used in the steelmaking industry due to the advantage of providing a large amount of high-temperature and stable hot blast for blast furnaces. To research the thermal efficiency and stability of external combustion hot blast stoves, the non-equilibrium porous medium model coupled with transient thermal analysis is used to discuss the characteristics of two types of external combustion hot blast stoves during the cyclic operation process. In this paper, a comparison of the numerical data and in situ data during one cycle to ensure the accuracy of the calculation, which of the results showed that the temperature maximum relative error value is within 3%. The numerical results displayed that the velocity and temperature distribution of fluid are mainly affected by pressure, flow rate, cycle time, and geometric structure, where the hot blast temperature is affected by the cycle time but the distribution of velocity and relative pressure are affected by the height of hot blast branch. It can be concluded that the flow field and the structure of type A hot blast stove are more stable than that of type B by comparing the results of two types of hot blast stoves.

Analysis of the Vertical Dynamic Response of SDCM Piles in Coastal Areas

The stiffened deep cement mixing (SDCM) pile, as a new type of rigid–flexible composite pile, significantly enhances the vertical bearing capacity of traditional precast piles, thus holding broad application prospects in the substructure construction of nearshore bridges and marine energy structures. This paper investigates the vertical dynamic response of SDCM piles through theoretical derivation and parameter analysis. Firstly, based on elastic dynamics theory and the three-phase porous media model, vertical vibration control equations for both SDCM piles and fractional-order viscoelastic unsaturated soils are established. Secondly, theoretical derivations yield exact analytical solutions for the surrounding dynamic impedance, top dynamic stiffness, and dynamic damping of the SDCM pile. Finally, through numerical examples and parameter studies, the impact mechanisms of physical parameters in the SDCM pile–unsaturated soil dynamic coupling system on the top dynamic stiffness and dynamic damping of the SDCM pile are analyzed. The research results presented in this paper indicate that reducing the radius of the rigid core pile while increasing the thickness of the exterior pile has a positive effect on enhancing its vibration resistance. Additionally, increasing the length of SDCM piles contributes to improved vibration performance. However, an increase in the elastic modulus of the cement–soil exterior pile is detrimental to the vibration resistance of the rigid composite pile. On the other hand, an increase in the elastic modulus of the concrete core pile only enhances its ability to resist vibration under low-frequency load excitation. Furthermore, enlarging the soil saturation, decreasing the intrinsic permeability, and enlarging the soil relaxation shear modulus have a significant positive impact on improving the vibration resistance of SDCM piles. In contrast, changes in porosity have a negligible effect on the ability to resist vertical vibrations of SDCM piles.

Microvoiding and constitutive damage modeling with artificial neural networks

Continuum models of porous media have revolutionized computational fracture mechanics for traditional ductile materials, but the inherent assumptions have limited generalizability to other target materials or loading conditions. Here, we adopt a series of artificial neural networks (ANNs) to predict both the microscopic voiding characteristics (void shape, porosity) and macroscopic stress–strain constitutive response of porous elasto-plastic materials under various deformation states. We train the ANNs on a dataset generated from finite element models of 3D representative volume elements (RVEs), each containing a discrete spherical void, subjected to combinations of loading states. Results show that the data-driven model is capable of interpolative predictions as well as some levels of extrapolative predictions across a wide range of initial porosities (0–20%) and loading states outside of the training dataset, even at high deformation strains which induce extensive material softening and void growth. Through transfer learning, we further demonstrate that the ANNs, originally trained on a specific porous material dataset, can be readily adapted to other porous materials with substantially different properties through a significantly reduced training dataset. We discuss the implications of this machine learning approach vis-à-vis the extensively-developed Gurson model for porous material damage and failure predictions.

Pressure Drop in a Metal Foam Centrifugal Breather: A Simulation Approach

One of the main issues faced in the operation of a metal foam centrifugal breather is the high pressure drop. This study investigates the pressure drop of a metal foam centrifugal breather. The numerical simulation research method is adopted. The DPM model is used to calculate the two-phase flow field of the metal foam breather, and the porous medium model is used to replace the metal foam at the breather. The resistance caused by the metal foam is replaced by a distributed resistance added to the fluid. The effects of flow rate, rotational speed, porosity, PPI (pores per inch), and temperature on the pressure drop of the breather are analyzed. The results indicate that rotational speed, flow rate, porosity, and PPI significantly influence the resistance of the metal foam centrifugal breather. The resistance of the breather is directly proportional to the rotational speed, flow rate, temperature, and metal foam pore density, and inversely proportional to the porosity. Temperature has a minor impact on the resistance of the metal foam centrifugal breather. Therefore, the metal foam centrifugal breather is more suitable for low-speed operating conditions.

Characteristics and optimization strategy of microwave thermal regeneration of spent activated carbon based on a multi-physical field model

Microwave thermal regeneration is an efficient and low-consumption way to recycle spent activated carbon. However, traditional experimental approaches are difficult to analyze the electromagnetic field distribution in the microwave cavity, heat and mass transfer process of adsorbates, and optimization of the microwave reactor. Therefore, in this work, a multi-phase porous media model coupled with electromagnetism, heat and mass transfer is established to study the characteristics of microwave thermal regeneration procedure and to propose an optimization strategy for the microwave reactor. The results showed that the absorption of microwave by the sample can be strengthened by adjusting the width to height ratio of the waveguide. The optimal waveguide size (width:length = 80 mm:10 mm) increased the microwave utilization efficiency from 65.4 % to 98.5 %. In addition, the combination of rotary and intermittent microwave heating significantly optimized the temperature uniformity in both lateral and vertical directions and reduced the microwave heating time. The combined microwave heating time was reduced from the initial 136 s to 80 s, saving 41 % of energy consumption. The temperature difference of the sample was also reduced from the initial 536 K to 191 K, and the covariance COVT decreased from 0.52 to 0.24. The results provide a valuable technical guideline for the optimization of the microwave reactor in order to improve the regeneration efficiency and the quality of the regenerated carbon.

Three-dimensional CFD modeling for hollow fiber gas separation membrane modules based on a dual porous media model

Mathematical modeling is crucial to optimizing the design of the hollow fiber membrane (HFM) module. A Computational Fluid Dynamics (CFD) model enables efficient three-dimensional (3D) simulations of HFM modules, which integrates a dual porous media approach, significantly reducing computational costs. Validation against alternative simulations and experimental data confirms its prediction capability (<7% deviation). Comparative analyses demonstrate the superior reliability of the 3D approach over one-dimensional simulations. Detailed velocity, pressure, and concentration profiles for the shell and tube sides reveal optimization opportunities such as dead zones within the module. Aerometric studies show significant pressure drops (>30%) for smaller fiber diameters (<100μm) on the permeate side. The model's adaptability suggests broader applications in membrane gas separation processes with modifications. This research highlights the efficacy of CFD modeling in enhancing the design and optimization of HFM modules, highlighting the cost savings of the dual porous media approximation.

Leak-Rate Through Carbon Brush Seals: Experimental Tests Versus Predictions From a Porous Medium Approach

Abstract This study presents a detailed comparative analysis between experimental leakage flow rates and numerical predictions for carbon brush seals with long bristles, utilizing a porous medium model approach. A series of tests were carried out on a static rig (without rotor rotation). The experimental setup allows tests under various interference conditions, revealing significant insights into the flow behavior through the brush seal. A numerical model based on the Darcy-Forchheimer equation is developed to interpret the complex flow dynamics within the brush seal, accounting for viscous, compressible and inertial effects. The study evaluates the impact of brush deformation and porosity on flow resistance, leveraging experimental data to refine the numerical model parameters. This investigation not only deepens the understanding of brush seal flow physics but also improves the predictive accuracy of the numerical model in simulating operational conditions.

Dot-array porous medium model for windscreen and its simulation accuracy analysis

Porous medium models have long been prevalent numerical computation tools. Although they exhibit swift computational speed, their accuracy in simulating windscreen perforation structures is challenged. This paper introduces the innovative dot-array porous medium (DAPM) model, which accurately portrays the perforation structure and material characteristics of a windscreen by establishing virtual holes on the porous medium. Not only does it simplify modeling by eliminating complex perforation processes, but it also adeptly simulates the flow behavior of the windscreen. The comprehensive comparison between the DAPM model and the physical mesh model, traditional porous medium model, as well as wind tunnel test results, demonstrates that the DAPM model not only possesses rapid computational speed but also delivers outstanding precision in results. In terms of velocity distribution, vortex distribution, and flow intensity in the flow field, the model indicates a high level of accuracy, clearly exceeding that of the porous medium model. Moreover, the DAPM model showcases high versatility and adjustability in practical applications. By adjusting dimension parameters, it demonstrates the capability to precisely simulate any windscreen with holes arranged in a matrix pattern. This research provides an efficient and reliable tool for the numerical simulation of windscreens, with broad application prospects.

Modeling of adsorption-controlled binary gas transport in ultratight porous media

Organic-rich ultratight porous media such as shales have complicated pore types and sizes, dictating their unique fluid transport and storage mechanisms. This paper introduces a diffusion-based binary gas (CH4 and CO2) transport model in such porous media, incorporating key transport and storage mechanisms. Binary gas mixture within the pore volume is divided into two domains: the free-phase and the sorbed-phase, both of which contribute to gas mass transport. Thermodynamic properties of the free phase are determined using the Peng-Robinson equation of state, while a modified extended Langmuir isotherm describes the sorbed phase. The bulk diffusion, Knudsen diffusion, and viscous diffusion are reconciled to describe binary gas transport in the free phase, while the surface diffusion is considered in the sorbed phase. The mass flux is finally related to the effective diffusion coefficient and the free-phase concentration gradient through coupling all transport mechanisms via the equivalent resister network model. The governing equations are solved numerically using a finite difference approach to simulate co-diffusion and counter-diffusion of a binary gas mixture in two nanoporous media, shale and coal.The results reveal that surface diffusion is more pronounced in coal than in shale due to coal's higher adsorption capacity. In co-diffusion cases, both free-phase and sorbed-phase concentrations decrease over time. However, the decline of sorbed-phase concentrations is slower than that of the free-phase. Moreover, CO2 tends to remain adsorbed within the coal matrix due to its stronger adsorption affinity, unlike CH4, which is more likely to flow out. In counter-diffusion cases, injected CO2 first accumulates near the fracture region and then diffuses further into the matrix. Despite shale's pore volume being twice that of coal, similar amounts of CO2 are injected, which can be attributed to coal's higher CO2 adsorption capacity.

On the influence of matrix flow in the hydraulic permeability of rough-walled fractures

Fractured porous media models may account for the influence of matrix flow in fracture permeability estimates through the slip boundary condition effect, i.e. permeable walls allow fluid to flow along them without viscous resistance. However, matrix flow may also create fluid pathways that unlock further fracture flow capacity, thus increasing its overall apparent permeability. We investigate this effect through numerical experiments by simulating fluid flow in a single fracture-matrix system with varying matrix permeability and calculating the apparent fracture permeability. We observe a consistent increase in fracture permeability with matrix permeability, which is yet underestimated by analytical models that factor in slip boundary conditions. Our study highlights the critical role of the surrounding porous matrix in accurately determining fracture permeability to prevent underestimations of the flow capacity of fractured porous media.

COMPARATIVE STUDY USING CFD OF COUNTER-CURRENT AND CO-CURRENT HYDROTREATING REACTORS USING JATROPHA CURCAS L VEGETABLE OIL

In this work, mathematical modeling and CFD simulation of two countercurrent and cocurrent hydrotreatment reactors were carried out, validating the results with a drained bed reactor (TBR), a commercial CoMo/γ-Al2O3 catalyst was used, the material the raw material was Jatropha Curcas L vegetable oil. The operating conditions were temperature 380 ° C, pressure 8 MPag. The kinetic model that was used considered 13 reactions that involve processes of decarboxylation, decarbonization, hydrodeoxygenation and hydrocracking reactions for triolein and tristearin triglycerides. The CFD simulation was carried out in Fluent 18.2 in a transient state and in 3D, considering the standard κ - ε turbulence models, Eulerian multiphase model and porous medium model, it was shown that the countercurrent reactor has less pressure drop than the countercurrent, the conversion the countercurrent reactor has a greater conversion of reactants of 99%, the generation of products from the countercurrent reactor has higher concentrations than the cocurrent reactor, this is because it has more contact areas between phases in the reactor.

Modeling CSF circulation and the glymphatic system during infusion using subject specific intracranial pressures and brain geometries

BackgroundInfusion testing is an established method for assessing CSF resistance in patients with idiopathic normal pressure hydrocephalus (iNPH). To what extent the increased resistance is related to the glymphatic system is an open question. Here we introduce a computational model that includes the glymphatic system and enables us to determine the importance of (1) brain geometry, (2) intracranial pressure, and (3) physiological parameters on the outcome of and response to an infusion test.MethodsWe implemented a seven-compartment multiple network porous medium model with subject specific geometries from MR images using the finite element library FEniCS. The model consists of the arterial, capillary and venous blood vessels, their corresponding perivascular spaces, and the extracellular space (ECS). Both subject specific brain geometries and subject specific infusion tests were used in the modeling of both healthy adults and iNPH patients. Furthermore, we performed a systematic study of the effect of variations in model parameters.ResultsBoth the iNPH group and the control group reached a similar steady state solution when subject specific geometries under identical boundary conditions was used in simulation. The difference in terms of average fluid pressure and velocity between the iNPH and control groups, was found to be less than 6% during all stages of infusion in all compartments. With subject specific boundary conditions, the largest computed difference was a 75% greater fluid speed in the arterial perivascular space (PVS) in the iNPH group compared to the control group. Changes to material parameters changed fluid speeds by several orders of magnitude in some scenarios. A considerable amount of the CSF pass through the glymphatic pathway in our models during infusion, i.e., 28% and 38% in the healthy and iNPH patients, respectively.ConclusionsUsing computational models, we have found the relative importance of subject specific geometries to be less important than individual differences in resistance as measured with infusion tests and model parameters such as permeability, in determining the computed pressure and flow during infusion. Model parameters are uncertain, but certain variations have large impact on the simulation results. The computations resulted in a considerable amount of the infused volume passing through the brain either through the perivascular spaces or the extracellular space.

Analysis and structure optimization of the flow and temperature fields of the large-scale hot air drying room

Large-scale hot air drying rooms play a crucial role as efficient drying equipment across various industries. The uniform distribution of hot air is a crucial factor influencing the drying quality of large-scale hot air drying rooms. This study focuses on camellia seeds as the drying subject. Building on a porous media model and the drying kinetics of camellia seeds, a CFD model of the drying room was established. Three-dimensional simulations of the internal flow and temperature fields were performed using CFD software, and the simulated results aligned well with experimental data. To improve the uniformity, this study introduced an optimized design featuring a combination of a Type E3 air guide hood with five guiding plates and a fan, selected based on optimized angles (θ1 = 5°, θ2 = 10°). Under the condition of improving the structure without introducing a new heat source, the optimization ensured a significant improvement in flow field uniformity while making the temperature field closer to the desired ideal temperature. This offers a reference for the design and research of hot air drying equipment and hot air drying rooms.

Application of Deep Neural Network Technology for Multi‐scale CFD Modeling in Porous Media

Application of Deep Neural Network Technology for Multi‐scale CFD Modeling in Porous Media

Wave propagation through a dense cluster of cylinders: a radiative transfer model

Clusters of cylinders are a useful way to model the wave propagation through several natural and complex media: crowds of people, forests, arrays of scatterers, or various materials. Depending on the absorption properties of the cylinders, as well as their size- and distance-to-wavelength ratio, different physical mechanisms are at play: scattering, viscous and thermal dissipation, absorption within the material of the cylinders themselves. We consider the low frequency case when the wavelength is larger than both the cylinder diameter and spacing. Most multiple scattering theories require larger than wavelength spacing and are not applicable in the case of dense clusters and at low frequencies. As a first approximation, a porous medium model is used to calculate the speed of sound in the cluster. However, this approach does not readily give access to the coherency of the signal. Recently, a radiative transfer approach was used to model forest acoustics to examine the transformation of the coherent sound field into an incoherent sound field. We use this approach to examine the coherent to incoherent field transition depending on the wavelength to diameter and spacing.

Numerical investigation on the core thermal hydraulic behavior of pool-type sodium-cooled fast reactor (SFR)

A thorough understanding of the reactor core thermal hydraulic behavior is essential for the design and safety analysis of Sodium-cooled Fast Reactors (SFR). Due to the application of hexagonal subassembly, the core thermal hydraulic behavior is significantly affected by the flow field within the subassemblies, the inter-wrapper region and the hot pool. Analysis of the core thermal hydraulic behavior requires a model coupling the three regions mentioned above, which has been identified as one of the thermal hydraulic challenges in SFR. In the present study, a 3D model that covers the three regions was developed for the core of the China Experimental Fast Reactor (CEFR) with the Computational Fluid Dynamic (CFD) code, Fluent. The inter-wrapper region and the hot pool were modeled in detail, while the subassemblies were modeled with a special porous medium model. The core thermal hydraulics behavior under steady state was studied, more specifically, information for the flow field distribution at the core outlet, the inter-wrapper flow and the duct wall temperature distribution was obtained. Under steady state, liquid sodium in the inter-wrapper region is supplied by the inner region of the hot pool. And it enters the inter-wrapper region from the core outer region and returns back to the hot pool inner region from the core central region. The inter-wrapper flow is cooled by non-fuel subassemblies and heated up by fuel subassemblies. For non-fuel subassembly, the ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies could reaches 96%; for fuel subassemblies, the maximum ratio of the total heat transfer rate between the inter-wrapper flow and the subassemblies to the heat generated within subassemblies is 2.45%. Significant temperature gradients have been observed on the duct wall, with maximum values of 156.69 K/m in the vertical direction and 2,196.00 K/m in the circumferential direction. The largest temperature gradient appears on the duct of subassemblies adjacent to the transition region of fuel subassemblies and non-fuel subassemblies.