Combined Effects of Salt and Microplastics on Evaporation and Crystallization Dynamics in Porous Media

We developed analytical models for surface- and capillary-assisted condensation and evaporation dynamics considering phase-change behavior in idealized wedge-shaped pores and in adsorbed liquid films as building blocks for condensation and evaporation in granular media. Phase-change rates are important for dust mobilization and deposition, vapor transport through partially saturated media, and for residence times of emitted combustion particulates. The basic wedge-film solution was scaled up to represent 3D transient evaporation and condensation processes within an assembly of rough spherical particles. Model comparisons with experimental data for evaporation from a single meniscus and condensation rates into sand samples show consistent agreement for a range of media and ambient conditions.

Modeling the impact of microbial activity on redox dynamics in porous media

For the coupled system of multilayer fluid dynamics in porous media, the modified characteristic finite difference fractional steps method applicable to parallel arithmetic is put forward and two‐dimensional and three‐dimensional schemes are used to form a complete set. Some techniques, such as calculus of variations, energy method, piecewise biquadratic interpolation, multiplicative commutation rule of difference operators, decomposition of high order difference operators and prior estimates are adopted. Optimal order estimates in L2 norm are derived to determine the error in the approximate solution. This method has already been applied to the numerical simulation of multilayer fluid dynamics in porous media. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 665–681, 2003.

Effects of microplastics on evaporation dynamics in porous media

Saline water evaporation from porous media with the corresponding surface salt crystallization patterns play a vital role in many environmental and engineering applications. While the impact of factors such as type and concentration of salt, particle size and angularity, and ambient temperature and humidity are relatively well characterized [1]–[3], the influence of wind and aerodynamic conditions on saline water evaporation and salt crystallization is not fully understood. We conducted a series of laboratory experiments in a wind tunnel to systematically investigate the effect of wind flow on saline water evaporation and dynamics of salt crystallization. Cylindrical sand columns (D: 5 cm – H: 20 cm) were placed in the test section of the wind tunnel. Surface of the samples were exposed to uniform mean wind velocities of 0.5 and 5 m/s. To keep samples fully saturated during the evaporation experiments, sand columns were supplied from Mariotte bottles containing 10, 15, and 20% NaCl solutions. Evaporation rates were monitored by measuring mass losses from Mariotte bottles, while salt crystallization patterns were captured using an optical camera positioned above the surface of columns. Preliminary results indicate that variation in aerodynamic conditions and turbulence patterns, driven by changes in wind velocity and surface roughness (due to crystal growth), significantly alter evaporation rates and salt crystallization process. Distinct crystallization patterns were observed with variation of wind velocity with possible influences on the evaporative fluxes. Using the measured data, we will identify the key effects of air flow regimes coupled with the salt concentration on evaporative losses and the evolution of crystallized salts at the surface, which will be important for a wide range of environmental and hydrological applications.[1] S. M. S. Shokri‐Kuehni, B. Raaijmakers, T. Kurz, D. Or, R. Helmig, and N. Shokri, “Water Table Depth and Soil Salinization: From Pore‐Scale Processes to Field‐Scale Responses,” Water Resour. Res., vol. 56, no. 2, Feb. 2020, doi: 10.1029/2019WR026707.[2] S. Jannesarahmadi, M. Aminzadeh, R. Helmig, D. Or, and N. Shokri, “Quantifying Salt Crystallization Impact on Evaporation Dynamics From Porous Surfaces,” Geophys. Res. Lett., vol. 51, no. 22, pp. 1–10, Nov. 2024, doi: 10.1029/2024GL111080.[3] M. Norouzi Rad and N. Shokri, “Effects of grain angularity on NaCl precipitation in porous media during evaporation,” Water Resour. Res., vol. 50, no. 11, pp. 9020–9030, Nov. 2014, doi: 10.1002/2014WR016125.

Bubble dynamics in porous media are of great importance in industrial and natural systems. Of particular significance is the impact that bubble‐related emissions (ebullition) of greenhouse gases from porous media could have on global climate (e.g., wetland methane emissions). Thus, predictions of future changes in bubble storage, movement, and ebullition from porous media are needed. Methods exist to predict ebullition using numerical models, but all existing models are limited in scale (spatial and temporal) by high computational demands or represent porous media simplistically. A suitable model is needed to simulate ebullition at scales beyond individual pores or relatively small collections (<10−4 m3) of connected pores. Here we present a cellular automaton model of bubbles in porous media that addresses this need. The model is computationally efficient, and could be applied over large spatial and temporal extent without sacrificing fine‐scale detail. We test this cellular automaton model against a physical model and find a good correspondence in bubble storage, bubble size, and ebullition between both models. It was found that porous media heterogeneity alone can have a strong effect on ebullition. Furthermore, results from both models suggest that the frequency distributions of number of ebullition events per time and the magnitude of bubble loss are strongly right skewed, which partly explains the difficulty in interpreting ebullition events from natural systems.

For evaporation in porous media, the gas–liquid interface displacement determines the phase distribution in porous media and hence the evaporation kinetics. In order to disclose the gas–liquid displacement in porous media during evaporation, the visualization experiments with the microfluidic pore networks are introduced. From these visualization experiments, the capillary valve effect, the capillary scissors effect, and the capillary instability effect are disclosed. These findings provide a deep understanding of the gas–liquid interface displacement in porous media during evaporation.

Evaporation of saline solutions from porous media, common in arid areas, involves complex interactions between mass transport, energy exchange and phase transitions. We quantified evaporation of saline solutions from heterogeneous sand columns under constant hydraulic boundary conditions to focus on effects of salt precipitation on evaporation dynamics. Mass loss measurements and infrared thermography were used to quantify evaporation rates. The latter method enables quantification of spatial and temporal variability of salt precipitation to identify its dynamic effects on evaporation. Evaporation from columns filled with texturally‐contrasting sand using different salt solutions revealed preferential salt precipitation within the fine textured domains. Salt precipitation reduced evaporation rates from the fine textured regions by nearly an order of magnitude. In contrast, low evaporation rates from coarse‐textured regions (due to low capillary drive) exhibited less salt precipitation and consequently less evaporation rate suppression. Experiments provided insights into two new phenomena: (1) a distinct increase in evaporation rate at the onset of evaporation; and (2) a vapor pumping mechanism related to the presence of a salt crust over semidry media. Both phenomena are related to local vapor pressure gradients established between pore water and the surface salt crust. Comparison of two salts: NaCl and NaI, which tend to precipitate above the matrix surface and within matrix pores, respectively, shows a much stronger influence of NaCl on evaporation rate suppression. This disparity reflects the limited effect of NaI precipitation on matrix resistivity for solution and vapor flows.

The prediction of clogging and permeability impairment dynamics in porous media is crucial for the optimization of various industrial and natural processes. This paper presents a novel machine learning-based approach for predicting the dynamics of throat clogging and permeability impairment due to fine migration within realistic porous media under varying hydro-physical conditions. A Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) numerical framework, employing a four-way coupling scheme, was used to generate the data for training and validation of the Machine Learning Model (MLM). One hundred and twenty distinct CFD-DEM simulations were performed to generate over 190,000 data points, at throat level, for the training of the MLM. Simulation cases encompassing ranges of porous media geometry, fine particle size, flow velocity, fine particle concentration, grains surface roughness, and fines and grains zeta potential. Geometries of porous media were extracted from high-resolution 3D images of natural sand obtained using micro-computed tomography imaging. The developed MLM predicts the temporal evolution of clogged throats and permeability impairment. The MLM was established by connecting three Machine Learning Sub-Models (MLSMs). The first is a throat-classification MLSM; which classifies the throats based on their location and size to identify clogged throats. Subsequently, a pore volume regression MLSM is implemented to identify the pore volume at which each clogged throat becomes clogged. Finally, the permeability impairment regression MLSM predicts the permeability reduction based on the clogged throat's information and pore volumes associated with clogging. The throats classification in the final MLM showed an accuracy of 95% in predicting clogged throats when compared to direct CFD-DEM simulations whereas the prediction of the permeability impairment had an R-squared value of 0.99. The MLM developed in this study stands as a robust framework for precisely quantifying key microscale parameters; where its predictions were used to quantify the significance of altering the hydro-physical parameters on the microscale parameters of the clogging dynamics. The proposed MLM provides an accurate and fast prediction of porous media clogging and permeability impairment dynamics, with potential applications in various industries, including oil and gas, environmental engineering, and material science.

Interfacial Heat Transport in Highly Permeable Media - A Finite Volume Approach Effective Thermal Properties of Hollow-Sphere-Structures - A Finite Element Approach Thermal Properties of Composite Materials and Porous Media: Lattice-Based Monte Carlo Approaches Fluid Dynamics in Porous Media - A Boundary Element Approach Analytical Methods for Heat Conduction in Composites and Porous Media Modeling of Composite Heat Transfer in Open-Cellular Porous Materials at High Temperatures Thermal Conduction Through Porous Systems Thermal Property of Lotus-Type Porous Copper and Application to Heat Sinks Thermal Characterization of Open-Celled Metal Foams by Direct Simulation Heat Transfer in Open-Celled Foams Subjected to Oscillating Flow Radiative and Conductive Thermal Properties of Foams On the Application of Optimization Techniques to Heat Transfer in Cellular Materials

Impact of type of salt and ambient conditions on saline water evaporation from porous media

Fluid dynamics in porous media with Sailfish

The influences of restitution coefficient, e n , interparticle friction, μ , and size ratio, R , on gravity-driven percolation of fine particles through static beds of larger particles in the free-sifting regime ( R ≳ 6.5 ) remain largely unexplored. Here, we use discrete element method simulations to study the fine particle percolation velocity, v p , and velocity fluctuations, v rms , for 7 ≤ R ≤ 50 and a range of e n and μ . Varying e n modulates the degree of particle excitation and thereby alters the nature of particle trajectories: at low e n , percolation is dominated by gravity, whereas increasing e n amplifies velocity fluctuations thereby reducing the mean percolation velocity. Increasing μ decreases v rms but its influence on v p varies with v rms , decreasing v p for low v rms and increasing v p for high v rms . Although the influence of size ratio is weaker, larger values of R increase both v p and v rms . We also assess the influence of different excitation mechanisms, specifically using static, randomly excited, and sheared beds, finding that an inverse correlation between v p and v rms persists across all cases and is well-described by the Drude model, where increased scattering reduces mobility, when v rms is large. However, for weakly excited particles with low v rms , the Drude analogy breaks down. In this regime, we introduce a staircase-inspired model that accounts for the gravitationally dominated percolation behavior. These findings provide fundamental insight into the mechanisms governing percolation dynamics in porous media and granular systems.

This article highlights a few milestones in the evolution of NMR techniques during the last four decades as far as the author had the pleasure to have a moderate share. The focus is on field-cycling NMR relaxometry, field-gradient NMR diffusometry, magnetic resonance imaging, and multidimensional NQR methods. Applications refer to polymer dynamics, fluid dynamics in porous media, anomalous transport properties, biological systems, etc. Keywords: field-cycling NMR relaxometry; field-gradient NMR diffusometry; NQR imaging; NQR 2D exchange spectroscopy; flow-velocity NMR mapping; electric current density NMR mapping; electro-osmotic flow NMR mapping; polymer dynamics; anomalous transport; dynamics in porous media and at surfaces

The accuracy of different model equations of sorption dynamics in porous media is analyzed. Analytical solutions of the equations are obtained for a rectangular isotherm.