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This study explores hydrogen production via steam methane reforming (SMR) within complex Voronoi catalytic foams. Pioneering pore-scale analysis unveils the intricate interplay between foam geometry and SMR performance, surpassing conventional macro-scale studies. The highly intricate Voronoi foams intrigue due to their maximized surface area and efficient heat transfer. The research meticulously examines the combined effects of various factors like inlet velocity, temperature, foam properties, and steam-to-carbon ratio on hydrogen yield. Employing OpenFOAM's finite volume method, pore-scale simulations were conducted. Each investigated parameter significantly impacted hydrogen production, with temperature boasting the most remarkable influence. A 142.5% surge in hydrogen production was observed when increasing the temperature from 1100 to 1200 K. Lengthening the foam from 5 mm to 10 mm yielded a 90% increase. This groundbreaking study highlights the immense potential of Voronoi foams to revolutionize SMR processes, paving the way for cleaner and more sustainable energy solutions. [Display omitted] • The SMR process is simulated in a catalytic environment with pore-scale perspective. • Effect of velocity, temperature, S/C ratio & porosity on H 2 generation is analyzed. • Temperature has a greater impact on hydrogen mass flow rates. • Voronoi catalytic foam structure can highly affect heat transfer & hydrogen production. • 90% increase in hydrogen production rate observed by doubling the length of the foam. [ABSTRACT FROM AUTHOR]

• The relationship between the DLVO potential energy and the physical-chemical properties. • The relationship between the particle deposition rate and energy barrier. • Relative porosity variation in the porous media coating different grain material. • The fluctuation of permeability reduction relating to bridging and bridge collapse. In this study, we investigated the effect mechanism of the grain material of artificial porous media coating quartz sand (SiO 2), titanium dioxide (n-TiO 2), zinc oxide (ZnO) and polystyrene (PS) on the motion and deposition of suspended particles. First, the relationship was deeply analysed between the DLVO potential energy and the physico-chemical properties of grain material, including the Hamaker constant and surface zeta potential. Second, the lattice Boltzmann method-immersed moving boundary-discrete element method (LBM-IMB-DEM) was used to investigate the motion characteristics of suspended particles and their effects, including the penetration rate, deposition rate, porosity reduction and the porosity-permeability relations. Third, the relations were innovatively explained between the energy barrier and the particles bridging and bridge collapse which cause the fluctuation of permeability reduction. The main results are as follows. (1) The descending order of the energy barrier between suspended particle and grain material is SiO 2 , ZnO, PS and n-TiO 2 , which is the same as that of the surface zeta potential of grain material. (2) For the suspended particles with the same size, the higher potential energy and Primary energy minimum (PEM) enhance the penetration rate. The particle deposition rate in porous media coating n-TiO 2 is higher than others. (3) The highest non-uniformity of the porosity reduction occurs in the porous media coating the material with the lowest energy barrier. (4) For the grain material with lower energy barrier, the fluctuation frequency of permeability reduction is lower owing to the longer bridging time. [ABSTRACT FROM AUTHOR]

Porous media have been extensively used for the enhancement of heat transfer, due to their large specific surface area. In many cases, the flow and heat transfer in porous media are also coupled with other flow patterns, such as the channel flow. This work investigates numerically a non-isothermal three-dimensional mixing process from a rectangular channel and a porous medium to reveal the influence of the structural parameters on the flow and heat transfer characteristics in the coupled system. The detailed heat and momentum transport behavior at the coupled interface are analyzed at the pore-scale. Correlations of the friction factor and the Nusselt number within the porous media are proposed as functions of the Reynolds number, porosity, velocity ratio, and pore size. Results from the pore-scale simulations are also used to improve the less-cost representative-elementary-volume-scale numerical model, which can be further used for the modeling of relevant engineering problems. [ABSTRACT FROM AUTHOR]

Gaseous flow through ultra-tight porous media, e.g. shale and some high-performance insulation materials, is often rarefied, invalidating an analysis by the continuum flow theory. Such rarefied flows can be accurately described by the kinetic theory of gases which utilizes the Boltzmann equation and its simplified kinetic models. While discrete velocity methods have been successful in directly solving these equations, the immense potential of a particle-based solution of the variance-reduced Boltzmann-BGK (Bhatnagar–Gross–Krook) equation for rarefied flows in porous media has not been exploited yet. Here, a parallel solver based on the low variance deviational simulation Monte Carlo method is developed for 3D flows, which enables pore-scale simulations using digital images of porous media samples. The unique advantage of this particle-based formulation is in providing additional insights regarding the multi-scale nature of the flow and surface/gas interactions via two new parameters, i.e. pore and surface activity, respectively. Together, these two parameters can identify key flow properties of the porous media. The computational efficiency and accuracy of the current method has also been analysed, suggesting that this new solver is a powerful simulation tool to quantify flow properties of ultra-tight porous media. [ABSTRACT FROM AUTHOR]

Pore-scale studies of premixed gas combustion in a packed bed is conducted to study the flow and thermal non-equilibrium phenomenon in packed bed. The 3D random packed bed is generated using the EDEM software and solid surface radiation is computed using Discrete Ordinates (DO) model. The simulations are carried out using a commercial software package based on the finite volume method. It is shown that the local variation of species mass fraction, reaction rate et al. in pores near the flame front is significant, the radiation heat flux is transferred layer-by-layer. Cold flow simulation without reaction reveals that flow non-equilibrium is one of the essential characteristics of packing bed and increase in flow velocity leads to intensify non-equilibrium phenomenon. The distributions for content of axial velocity and gas temperature are wave-like shape in the burner and vary with time.

Highlights • Simulations are carried out to model longitudinal thermal dispersion at pore-scale. • Thermal dispersion is a function of the thermal properties and flow conditions. • A characterization diagram is constructed to identify thermal dispersion regime. • Viscous fingering is shown to increase the longitudinal thermal dispersion. Abstract In non-isothermal flows through porous media, the rate of heat transport across the domain and the distribution of temperature profile are strongly affected by the thermal properties of the fluid and solid phases, flow conditions, and the topological geometry of the pore structure. The combined effect of these parameters on the dynamics of heat transfer is generally characterized by the thermal dispersion coefficient. In this study, we model thermal dispersion in granular porous media using pore-scale numerical simulations. The flow and heat transport equation are solved in a porous domain at the pore-level to obtain the distribution of temperature inside the fluid phase and solid grains. The effluent temperature profile at the outlet is then fitted to the analytical solution of the macroscale heat advection-dispersion equation to determine the longitudinal component of the effective thermal dispersion tensor. Several simulation runs are carried out to investigate the effect of Peclet number, fluid to solid thermal conductivity and heat capacity ratios, and the temperature-dependent viscosity on the variation of the longitudinal thermal dispersion coefficient. The results indicate the existence of different thermal dispersion regimes separated by a threshold Peclet number. Below the threshold, thermal dispersion is dominated by conduction and longitudinal dispersion coefficient is equal to the effective thermal conductivity of the porous medium. Above the threshold, there is a transition region in which both conduction and advection are responsible for the heat ttansport. At higher Peclet numbers, dispersion regime is advection-dominated and normalized dispersion coefficient increases with the Peclet number and thermal conductivity ratio whereas it decreases with the heat capacity ratio. In this regime, the relationship between dispersion coefficient and Peclet number follows a power-law functionality with the exponent decreasing with the heat capacity ratio. To summarize the results, a characterization diagram is constructed for thermal dispersion regime based on the values of Peclet number and thermal conductivity ratio. Finally, the presence of viscous fingering due to the monotonically increasing viscosity along the flow is observed to further increase the longitudinal thermal dispersion. The outcomes of this study are of great importance in the design, implementation, and performance optimization of thermal processes in granular porous media. [ABSTRACT FROM AUTHOR]

The present work attempts to identify the roles of flow and geometric variables on the scaling factor which is a necessary parameter for modeling the apparent viscosity of non-Newtonian fluid in porous media. While idealizing the porous media microstructure as arrays of circular and square cylinders, the present study uses multi-relaxation time lattice Boltzmann method to conduct pore-scale simulation of shear thinning non-Newtonian fluid flow. Variation in the size and inclusion ratio of the solid cylinders generates wide range of porous media with varying porosity and permeability. The present study also used stochastic reconstruction technique to generate realistic, random porous microstructures. For each case, pore-scale fluid flow simulation enables the calculation of equivalent viscosity based on the computed shear rate within the pores. It is observed that the scaling factor has strong dependence on porosity, permeability, tortuosity and the percolation threshold, while approaching the maximum value at the percolation threshold porosity. The present investigation quantifies and proposes meaningful correlations between the scaling factor and the macroscopic properties of the porous media. [ABSTRACT FROM AUTHOR]

Flows through porous filter walls of wall-flow diesel particulate filter are investigated using the lattice Boltzmann method (LBM). The microscopic model of the realistic filter wall is represented by randomly overlapped arrays of solid spheres. The LB simulation results are first validated by comparison to those from previous hydrodynamic theories and constitutive models for flows in porous media with simple regular and random solid-wall configurations. We demonstrate that the newly designed randomly overlapped array structures of porous walls allow reliable and accurate simulations for the porous wall-flow dynamics in a wide range of solid volume fractions from 0.01 to about 0.8, which is beyond the maximum random packing limit of 0.625. The permeable performance of porous media is scrutinized by changing the solid volume fraction and particle Reynolds number using Darcy’s law and Forchheimer’s extension in the laminar flow region. [ABSTRACT FROM AUTHOR]

Summary The Lattice Boltzmann (LB) method is an established prominent model for simulating water flow at pore scale in saturated porous media. However, its application in unsaturated soil is less satisfactory because of the difficulties associated with most two-phase LB models in simulating immiscible fluids, such as water and air, which have contrasting densities and viscosities. While progress has been made in developing LB models for fluids with high density ratio, they are still prone to numerical instability and cannot accurately describe the interfacial friction on water–air interface in unsaturated media. Considering that one important application of the LB model in porous materials is to calculate their hydraulic properties when flow is at steady state, we develop a simple LB model to simulate steady water flow at pore scale in unsaturated soils. The method consists of two steps. The first one is to determine water distribution within the soil structure using a morphological model; once the water distribution is known, its interfaces with air are fixed. The second step is to use a single-phase LB model to simulate water flow by treating the water–air interfaces as free-flow boundaries where the shear resistance of air to water flow is assumed to be negligible. We propose a method to solve such free-flow boundaries, and validate the model against analytical solutions of flows of water film over non-slip walls in both two and three dimensions. We then apply the model to calculate water retention and hydraulic properties of a medium acquired using X-ray computed tomography at resolution of 6 μm. The model is quasi-static, similar to the porous network model, but is an improvement as it directly simulates water flow in the pore geometries acquired by tomography without making any further simplifications. [ABSTRACT FROM AUTHOR]

A lattice Boltzmann color-fluid model, which was recently proposed by Liu et al. (2012) based on a concept of continuum surface force, is improved to simulate immiscible two-phase flows in porous media. The new improvements allow the model to account for different kinematic viscosities of both fluids and to model fluid–solid interactions. The capability and accuracy of this model is first validated by two benchmark tests: a layered two-phase flow with a variable viscosity ratio, and a dynamic capillary intrusion. This model is then used to simulate liquid CO 2 (LCO 2 ) displacing water in a dual-permeability pore network. The extent and behavior of LCO 2 preferential flow (i.e., fingering) is found to depend on the capillary number ( Ca ), and three different displacement patterns observed in previous micromodel experiments are reproduced. The predicted variation of LCO 2 saturation with Ca , as well as variation of specific interfacial length with LCO 2 saturation, are both in reasonable agreement with the experimental observations. To understand the effect of heterogeneity on pore-scale displacement, we also simulate LCO 2 displacing water in a randomly heterogeneous pore network, which has the same size and porosity as the simulated dual-permeability pore network. In comparison to the dual-permeability case, the transition from capillary fingering to viscous fingering occurs at a higher Ca , and LCO 2 saturation is higher at low Ca but lower at high Ca . In either pore network, the LCO 2 –water specific interfacial length is found to obey a power-law dependence on LCO 2 saturation. [ABSTRACT FROM AUTHOR]

Highlights: [•] In this work pore-scale CFD simulations of several porous media were performed. [•] Colloidal particle deposition due to Brownian motions and steric interception were analyzed. [•] Several models representing porous media with different characteristics were considered. [•] Results highlight strong deviations from the extended Levich law for many-collector systems. [•] Results also show deviations due to the irregular shape of the collectors. [ABSTRACT FROM AUTHOR]

Pore-scale heat and fluid flow simulation through reconstructed porous media is presented with the aim of investigating the physics of heat flux splitting at the boundary of porous media. As such, the effects of the solid to fluid thermal conductivity ratio, porosity, pore-scale Reynolds number, Prandtl number and heat conduction within the solid matrix are investigated. The results of the present study for heat transfer coefficient and pressure drop are compared with available experimental data and good agreement was observed. The validated results are then used to investigate the validity of the existing volume-averaged models. It was observed that while results based on the volume-averaged models are reasonably close to current predictions for $$\varepsilon \le 0.7$$, the discrepancy between the two becomes notable for higher porosities. While existing models rely exclusively on porosity and thermal conductivity ratio, our newly proposed correlations show the effects of Reynolds number on the heat split mechanism for high porosities. On the other hand, the Prandtl number, at least for the range of parameters studies here, is found to be less influential on the boundary heat split mechanism. [ABSTRACT FROM AUTHOR]

Abstract: Laminar steady forced convection through an array of disconnected conducting cylindrical fins is simulated by implementing a pore-scale numerical simulation. Effects of fin array porosity, fin arrangements, pore-scale Reynolds number, and the solid to fluid thermal conductivity ratio, on the heat flux bifurcation at the uniformly heated wall are investigated. The results show that decreasing the Reynolds number or increasing the solid to fluid thermal conductivity ratio monotonically increases the solid to fluid wall heat flux ratio. It is also observed that solid to fluid heat flux ratio increases with increasing the porosity. The obtained results have been compared to available models in the literature. While in some cases the results are close, errors associated with available models are analyzed and accurate correlations for heat flux bifurcation are proposed. [Copyright &y& Elsevier]

Abstract: We investigate the possibility of using nominally second-order-accurate techniques for resolving flow about solid boundaries as a means of improving accuracy and reducing grid resolution requirements in pore-scale simulations. An LBGK method is used to calculate flow in several geometries of increasing complexity, using a first-order accurate and two nominally second-order-accurate methods for no-slip boundaries. The geometries include uniform flow past an isolated sphere, quadratic flow past a sphere near a wall, flow through a BCC array of spheres, and through a randomly packed bed of spheres. The packed bed flows are also used to compare hydrodynamic dispersion results. The results confirm second-order-accurate behavior where Navier–Stokes flows are clearly developed. However 3D pore-scale simulations involve a trade-off between resolution of the flow and the number of pore spaces, and there is a resolution threshold, below which certain flow features, such as recirculation, are not resolved. We conjecture that most simulations will tend to operate near this threshold because of the competing demands for resolution and statistical accuracy. We consider local flow features and the velocity distribution, in addition to hydraulic permeability and drag, to provide a fuller understanding of accuracy near this threshold. [Copyright &y& Elsevier]

Pore-scale studies of premixed gas combustion in a packed bed is conducted to study the flow and thermal non-equilibrium phenomenon in packed bed. The 3D random packed bed is generated using the EDEM software and solid surface radiation is computed using Discrete Ordinates (DO) model. The simulations are carried out using a commercial software package based on the finite volume method. It is shown that the local variation of species mass fraction, reaction rate et al. in pores near the flame front is significant, the radiation heat flux is transferred layer-by-layer. Cold flow simulation without reaction reveals that flow non-equilibrium is one of the essential characteristics of packing bed and increase in flow velocity leads to intensify non-equilibrium phenomenon. The distributions for content of axial velocity and gas temperature are wave-like shape in the burner and vary with time. [ABSTRACT FROM AUTHOR]

Abstract: Modelling adsorptive solute transport in soils needs a number of parameters to describe its reaction kinetics and the values of these parameters are usually determined from batch and displacement experiments. Some experimental results reveal that when describing the adsorption as first-order kinetics, its associated reaction rates are not constants but vary with pore water velocity. Explanation of this varies but an independent verification of each explanation is difficult because simultaneously measuring the spatiotemporal distributions of dissolved and adsorbed solutes in soils is formidable. Pore-scale modelling could play an important role to address this gap and has received increased attention over the past few years. This paper investigated the transport of adsorptive solute in a simple porous medium using pore-scale modelling. Fluid flow through the void space of the medium was assumed to be laminar and in saturated condition, and solute transport consisted of advection and molecular diffusion; the sorption and desorption occurring at the fluid–solid interface were modelled as linear first-order kinetics. Based on the simulated spatiotemporal distribution of dissolved and adsorbed solutes at pore scale, volumetric-average reaction kinetics at macroscopic scale and its associated reactive parameters were measured. Both homogeneous adsorption where the reaction rates at microscopic scale are constant, and heterogeneous adsorption where the reaction rates vary from site to site, were investigated. The results indicate that, in contrast to previously thought, the macroscopic reaction rates directly measured from the pore-scale simulations do not change with pore velocity under both homogeneous and heterogeneous adsorptions. In particular, we found that for the homogeneous adsorption, the macroscopic adsorption remains first-order kinetic and can be described by constant reaction rates, regardless of flow rate; whilst for the heterogeneous adsorption, the macroscopic adsorption kinetics continues not to be affected by flow rate but is no longer first-order kinetics that can be described by constant reaction rates. We discuss how these findings could help explain some contrary literature reports over the dependence of reaction rates on pore water velocity. [Copyright &y& Elsevier]