Letteratura scientifica selezionata sul tema "Intra-pore phenomena"

Mathematical modelling of batch adsorption of Oryzanol separation from Rice Bran Oil (RBO) has been set-up and tested by generated experimental data. The proposed model takes into account mass transfer and equilibrium phenomena. The effects of intra-particle gradient were considered, so the adsorption rate is controlled by the rate of solute mass transfer from the bulk liquid to the surface of particles and the intra-particle diffusion. In this model, the rate of Oryzanol mass transfer from the bulk liquid to the surface of the particle is described by film theory, while the intra-particle diffusion is assumed to be through the liquid inside the pore. Furthermore the Oryzanol in the liquid in the pore was assumed to be in equilibrium with the Oryzanol on the adjacent pore surface, in which equilibrium model applied was coefficient distribution approach. The values of the parameters involved in the models were obtained by curve fitting to the experimental data. It turned out that model proposed can quantitatively describe the batch adsorption of Oryzanol adsorption from rice bran oil with silica gel.

Design of porous carbon-based electrode materials and derived porous electrode structures is crucial for the performance of electrochemical energy storage and conversion devices. In that context carbon-based electrode material building blocks with well-defined properties are desired. Such properties include controlled morphology (preferably spherical), particle size, and intra-particle porosity along with controlled composition, surface chemistry, and processability. These factors influence the particle arrangement and electrode structure during processing, as well as electrolyte interaction, distribution, and mass transport phenomena within the electrode. In this work, we introduce a hard-templating method for producing highly uniform meso- and macroporous N-doped carbon nanospheres with independently tuneable pore and particle sizes, serving as a versatile material platform for the bottom-up design of 3D porous carbon electrodes. We could thereby customize the pore sizes between approximately 10 to 100 nm at a constant particle size, while particle sizes between 50 and 300 nm could be achieved for a constant pore size. Other physicochemical parameters such as chemical composition, graphitization, and surface functionalization remained constant across all samples, allowing for the exclusive investigation of pore and particle size effects independently from each other. We further used our different N-doped carbon nanospheres as building blocks for 3D porous electrodes and studied these in electrochemical double-layer capacitors with the aim to (i) showcase the versatility of our materials and (ii) examine pore and particle size effects on the performance. Indeed, electrochemical double-layer capacitors serve as an excellent model system for such investigations due to their sensitivity to carbon particle surface area, pore size, and mass transport phenomena within the 3D percolated structure of porous carbon electrodes.

Atomistic and continuum scale modeling efforts have shown that the shock-induced collapse of porosity can occur via a wide range of mechanisms dependent on pore morphology, the shockwave pressure, and material properties. The mechanisms that occur under weaker shocks tend to be more efficient at localizing thermal energy but do not result in high, absolute temperatures or spatially large localizations compared to mechanisms found under strong shock conditions. However, the energetic material 1,3,5-trinitro-2,4,6-triaminobenzene (TATB) undergoes a wide range of collapse mechanisms that are not typical of similar materials, leaving the collapse mechanisms and the resultant energy localization from the collapse, i.e., hotspots, relatively uncharacterized. Therefore, we present the pore collapse simulations of cylindrical pores in TATB for a wide range of pore sizes and shock strengths that trigger viscoplastic collapses that occur almost entirely perpendicular to the shock direction for weak shocks and hydrodynamic-like collapses for strong shocks that do not break the strong hydrogen bonds of the TATB basal planes. The resulting hotspot temperature fields from these mechanisms follow trends that differ considerably from other energetic materials; hence, we compare them under normalized temperature values to assess the relative efficiency of each mechanism to localize energy. The local intra-molecular strain energy of the hotspots is also assessed to better understand the physical mechanisms behind the phenomena that lead to a latent potential energy.

The production of high-quality Ceramic-Matrix Composites often includes matrix deposition by Chemical Vapour Infiltration (CVI), a process which involves many phenomena such as gas transport, chemical reactions, and structural evolution of the preform. Control and optimization of this high-tech process are demanding for modelling tools. In this context, a numerical simulation of CVI in complex 3D images, acquired e.g. by X-ray Computerized Microtomography, has been developed. The approach addresses the two length scales which are inherent to a composite with woven textile reinforcement (i.e. inter- and intra-bundle), with two numerical tools. The small-scale program allows direct simulation of CVI in small intra-bundle pores. Effective laws for porosity, internal surface area and transport properties as infiltration proceeds are produced by averaging. They are an input for the next modelling step. The second code is a large-scale solver which accounts for the locally heterogeneous and anisotropic character of the pore space. Simulation of the infiltration of a whole composite material part is possible with this program. Validation of these tools on test cases, as well as some examples on actual materials, are shown and discussed.

Endovascular coiling is an acceptable treatment of intracranial aneurysms, yet long term follow-ups suggest that endovascular coiling fails to achieve complete aneurysm occlusions particularly in wide-neck and giant aneurysms. Placing of a stentlike device across the aneurysm neck may be sufficient to occlude the aneurysm by promoting intra-aneurysmal thrombosis; however, conclusive evidence of its efficacy is still lacking. In this study, we investigate in vitro the efficacy of custom designed flow divertors that will be subsequently implanted in a large cohort of animals. The aim of this study is to provide a detailed database against which in vivo results can be analyzed. Six custom designed flow divertors were fabricated and tested in vitro. The design matrix included three different porosities (75%, 70%, and 65%). For each porosity, there were two divertors with one having a nominal pore density double than that of the other. To quantify efficacy, the divertors were implanted in a compliant elastomeric model of an elastase-induced aneurysm model in rabbit and intra-aneurysmal flow changes were evaluated by particle image velocimetry (PIV). PIV results indicate a marked reduction in intra-aneurysmal flow activity after divertor implantation in the innominate artery across the aneurysm neck. The mean hydrodynamic circulation after divertor implantation was reduced to 14% or less of the mean circulation in the control and the mean intra-aneurysmal kinetic energy was reduced to 29% or less of its value in the control. The intra-aneurysmal wall shear rate in this model is low and implantation of the flow divertor did not change the wall shear rate magnitude appreciably. This in vitro experiment evaluates the characteristics of local flow phenomena such as hydrodynamic circulation, kinetic energy, wall shear rate, perforator flow, and changes of these parameters as a result of implantation of stentlike flow divertors in an elastomeric replica of elastase-induced saccular aneurysm model in rabbit. These initial findings offer a database for evaluation of in vivo implantations of such devices in the animal model and help in further development of cerebral aneurysm bypass devices.

La pyrolyse du bois est un processus crucial dans la science de la sécurité incendie car elle affecte la décomposition thermique et le comportement de combustion des matériaux. Le bois est un composite biopolymères (cellulose, hémicellulose et lignine) qui subit une pyrolyse complexe, produisant du charbon solide, du goudron et des gaz. Le processus de pyrolyse modifie également certaines caractéristiques importantes de l’échantillon (densité, conductivité thermique, capacité thermique, porosité, perméabilité, émissivité...) qui évoluent tout au long de la réaction de décomposition. La compréhension de ces transformations est cruciale pour la modélisation du comportement du feu des solides. Les évolutions des masses normalisées finales entre les expériences ATG et en cône calorimètre remettent en cause les modèles de taux de réaction solides existants. Les modèles actuels supposent souvent un ordre de réaction égal à 1, ce qui conduit à des inexactitudes lorsque l’ordre de réaction diffère de 1. Pour surmonter ces lacunes, un nouveau modèle basé sur la conversion, appelé ”Masse Initiale Virtuelle”, est proposé. Ce modèle est basé sur des données issues d’essais ATG. Il calcule la vitesse de chaque réaction dans le cas de mécanismes de pyrolyse complexes, avec de nombreuses réactions séquentielles et compétitives et a été implémenté en C++. Le code C++ de ce modèle est intégré avec l’outil DAKOTA pour permettre l’optimisation multi-objectif par algorithme génétique (MOGA) des paramètres cinétiques sur plusieurs vitesses de chauffage. Ce modèle de « Masse Initiale Virtuelle » est intégré dans la boîte à outils d’analyse des matériaux poreux basée sur OpenFOAM (PATO), un outil Open Source créé par la NASA. D’autres modèles de transferts de masse, de chaleur et de conservation des espèces en plus des propriétés des matériaux sont créés dans ce nouveau cadre. Un modèle informatique pour les réactions secondaires (réactions en phase gazeuse qui produisent du charbon secondaire) est implémenté dans PATO. Les simulations des essais en cône calorimètre sont effectuées dans des modèles 1D et 2D axisymétriques pour explorer l’influence des propriétés anisotropes du bois, en particulier l’orientation de ses fibres. La comparaison des modèles avec et sans réactions secondaires démontre le rôle de ces dernières dans la distribution de la chaleur et la production de charbon secondaire. Ce résultat explique la différence de masse finale observée expérimentalement entre les tests en ATG et en cône calorimètre. La comparaison des résultats expérimentaux et numériques montre la pertinence de cette approche pour simuler le comportement complexe de la pyrolyse du bois en mettant en évidence l’importance des voies de réaction, des réactions secondaires, du transfert de chaleur, du transfert de masse et des phénomènes d’interaction intra-pore
Pyrolysis of wood is a crucial process in fire safety science because it affects the thermal decomposition and combustion behavior of materials. Wood, a composite of biopolymeric components (cellulose, hemicellulose and lignin) undergoes complex pyrolysis to yield solid char, tar and gases as it thermally decomposes. The pyrolysis process also changes some important characteristics of the sample (density, thermal conductivity, heat capacity, porosity, permeability, emissivity...) that evolve throughout the reaction. Understanding these transformations is crucial for the correct modeling of fire behavior and material response under different thermal conditions. Different final normalized mass between TGA and cone calorimeter experiments challenge existing solid reaction rate models, according to experimental studies. Current models often assume a reaction order of 1, which oversimplifies the complexity of wood pyrolysis and leads to inaccuracies when the reaction order differs from 1. To overcome these shortcomings, a brand new conversion-based model, called ”Virtual Initial Mass”, is proposed. This model, based on TGA data, calculates the reaction rate for each reaction in complicated pyrolysis mechanisms. It supports mechanisms with numerous sequential and competitive reactions and has been implemented in C++. The C++ code for this model is integrated with the DAKOTA toolkit to perform multi objective genetic algorithm (MOGA) optimization of kinetic parameters for multiple heating rates. This ”Virtual Initial Mass” model is integrated in the Porous material Analysis Toolbox based on OpenFOAM (PATO) an Open Source tool distributed by NASA. Further mass transfer, heat transfer, species conservation models in addition to material properties are created within this new framework. A computational model for secondary reactions (gas-phase reactions that produce secondary char) is implemented in PATO. These secondary reactions solidify the sample and distribute heat back into the system. Simulations of cone calorimeter tests are performed in 1D and 2D axisymmetric models to explore the influence of anisotropic wood properties, particularly the orientation of wood fibers. Comparison of models with and without secondary reactions demonstrates their role in heat distribution and secondary char production and points out the experimentally observed difference in normalized mass between TGA and cone calorimeter tests. The model is verified by comparison with experimental results to show that it can simulate the complicated behavior of wood pyrolysis as well as emphasizes the importance of reaction pathways, secondary reactions, heat transfer, mass transfer and intra-pore interaction phenomena

Abstract The very singular pore network architecture of thermal spray coating results from the combination of several phenomena occurring during the coating buildup process. Close pores, usually of large dimensions, result from stacking defaults when impinging particles spread onto previously deposited layers. Intra-lamellar cracks, perpendicular to the substrate surface, develop mostly in ceramic lamellae during solidification. Inter-lamellar cracks, parallel to the substrate surface, depend significantly from the surface tension characteristics during the particle spreading stage. One way or another, these characteristics are related to the processing parameters implemented to manufacture the coating and they significantly modify the coating characteristics, their cohesion, their compliance and their impermeability, among the most significant. Al2O3-TiO2 (13% wt.) coatings were atmospheric plasma sprayed implementing several sets of processing parameters, among which power parameters (i.e., arc current intensity, plasmas gas flow rates, etc.), feedstock injection parameters (i.e., carrier gas flow rate, injector internal diameter, etc.) and environment parameters (i.e., spray angle, etc.) were varied. Pore contents were analyzed implementing image analysis. Pore network connectivity was analyzed implementing an electrochemical test: the higher the passivation potential of the substrate, the higher the coating pore network connectivity.

Overpressure is one of the geological phenomena associated with significant pressure values on normal hydrostatic gradients. The excess pressure is caused by loading or unloading of sediments. To predict pore pressure values, the Eaton method is used. Supporting data such as wireline logs, formation pressure data, drilling mud weight data, 3D seismic data, and geochemical data, are used to support distribution and control overpressure in the study area. Seismic data processing uses two types of data namely PSDM seismic volume and data speed intervals velocity. Process interval data velocity from seismic is useful in making excess pressure distribution. Seismic PSDM volume is useful for subsurface geological imaging, where in the manufacturing process horizons and structures are determined. Top overpressure in each research well is in the Intra Gumai formation, while the overpressure distribution in the study area is also close to the peak of the Gumai formation. The mechanism of the cause of overpressure in the study area is the unloading mechanism in the form of smectite mineral that has undergone diagenetic processes into illite and hydrocarbon maturity. The overpressure distribution in the research area is associated with a sequence stratigraphy which has low permeability, which is controlled by the intra Gumai formation which has a small permeability to the intra gumai formation, in addition to the excess pressure distribution is also inseparable from the dismantling factor including Diatctite mineral diagenesis to the Ilit Excessive pressure is observed in any research well in Gumai.

ABSTRACT: In general, geomechanical experiments are conducted to measure the impact of changes in pressure (axial, radial and pore pressures) due to production or injection of fluids for instance. The change in reservoir rock strength can then be used to quantify for example the risks of subsidence, loss of seal integrity, fault reactivation and other effects when an oil or gas field is developed. In standard geomechanics tests we make a CT image of a plug (e.g., 1.5-inch diameter and 3-inch length) before and after a geomechanical experiment using a 50 μm voxel size. Hence, we get a snapshot in time of what the plug looked like before deformation (without pressures on the sample) and what the plug looks like after deformation (without pressures on the sample). We have developed a new triaxial rock deformation cell that can be operated inside a CT scanner and enables us to conduct triaxial tests on rock mini plugs (6 mm diameter and 12 mm length). This newly developed cell enables us to image the plugs at different stages during the deformation experiment without having to mount and unmount the sample in-between giving us snapshots of rock deformation during the experiment. 1. INTRODUCTION Geomechanical experiments are often conducted to measure the impact (in strains) of changes in axial, radial and pore pressures on a plug. Typically, in a triaxial compression test (σ1 > σ2 = σ3) the plug will be brought to its reservoir pressures for instance, where after the axial pressure will be increased until brittle or ductile failure of the plug. In general, one can describe the deformation in a triaxial test in three different stages: 1. Initial closure of pre-existing cracks and elastic deformation, 2. Linear combination of inelastic and elastic deformation, 3. Brittle deformation and localization (e.g. Pijnenburg et al., 2019a). In standard geomechanical tests (including but not limited to triaxial compression tests) applied stresses are known and induced strains will be measured during the test. We make X-ray computed tomography (CT) scans of the plug before and after test using typically a voxel resolution of 50 μm to get a snapshot of what the plug looked like before deformation and what the plug looked like after deformation (as described by: Baud et al, 2015). Both CT scans are performed without any stresses acting on the sample, using a high-resolution Bruker Skyscan 1275 scanner. From these CT scans before and after a geomechanical experiment at a 50 μm resolution it is, however, hard to infer evidence which deformation mechanisms are at play during deformation (e.g., inter-granular cracking/slip versus intra-granular cracking, e.g. Brantut et al., 2013; Tengattini et al., 2014; Hol et al., 2018; Pijnenburg et al., 2019b). Momentary phenomena in geomechanics like the onset of deformation and how this continues can be imaged in 4D (3D image, time-lapsed) using a CT translucent triaxial setup inside a CT scanner. The design of CT translucent triaxial devices is an ongoing field of development that started with imaging soil and loose sand packs (low pressures, e.g.: Viggiani et al., 2004), but continued into rock deformation (e.g.: Renard et al., 2016; Glatz et al., 2018; Voltolini et al., 2019; Butler et al., 2020; Cartwright-Taylor et al., 2020; Fusseis et al., 2022; Van Stappen et al., 2022; Freitas et al., 2024). We have developed a new triaxial rock deformation cell that can be operated inside one of our laboratory CT scanners (ZEISS Xradia versa 520). The mini-triaxial deformation cell has been designed and built in collaboration with MetaRock laboratories. This paper describes the operational parameters of this mini-triaxial cell, and we discuss the first results.

Abstract Yttria partially stabilized Zirconia (Y-PSZ) thermal barrier coatings (TBCs) have numerous applications as insulation layers onto gas turbine components. The main function of TBC is to enhance efficiency by increasing working temperature. These coatings are commonly manufactured using air plasma spraying. The characteristics of TBCs strongly depends on their pore and crack network architecture. Engineering the coating architecture by an adapted process is a prerequisite to modify TBC characteristics. Therefore, air plasma spray and in situ laser irradiation by diode laser processes were combined in this study to modify structural characteristics of TBCs. The coatings were remelted layer by layer during their deposition or alternately (i.e., an as-sprayed layer followed by an in situ remelted layer). This process was named MELTPRO. TBC apparent thermal conductivity was quantified implementing numerical computations based on 2-D real discrete structures. Coating thermal properties were correlated to their pore network architecture characteristics quantified by image analysis (i.e., nature, orientation, percentage, etc.). Moreover, thermal annealing at 1100°C were performed to compare sintering phenomenon of manufactured TBCs. Results show that the MELTPRO process permits: (i) to modify of the pore network architecture of as-sprayed TBCs. The porosity level increases by the in situ remelting process due to the formation of large horizontal cracks (as shown by image analysis). These horizontal cracks behave as thermal resistances and are responsible for the decrease of the coating thermal conductivity of about 30 % compared to the as-sprayed ones; (ii) to architecture differently the pore network for a constant thermal conductivity, because thermal conductivity and porosity level are not explicitly correlated; (iii) to improve the thermal insulation which remains unchanged after thermal annealing treatments: this seems to be due to the fact that the large cracks of remelted TBCs are less sensitive to sintering than inter and intra lamellar cracks of as-sprayed TBCs.

Abstract The Haynesville basin currently supplies ∼15% of total natural gas production in the United States. Demand is expected to rise significantly by 2030 to meet domestic needs and support growing LNG opportunities. ExxonMobil holds a contiguous acreage position in the southern part of the basin that has not been fully developed. In this study, we present an innovative workflow which integrates pressure and geologic data to predict production trends and optimize development in the Haynesville Basin. To understand pressure trends across the basin, we mapped reservoir pressures from well flowback data and seismic velocities across the field. We also mapped breakdown pressures recorded from fracking operations to understand the correlation with reservoir pressures, structural features and production performance to identify regions favorable for development. Our data from the pressure mapping study suggests that the damage zones associated with listric fault complexes cause degradation in reservoir and breakdown pressures resulting in degraded production performance in wells drilled adjacent to the faults. Breakdown Pressures can also tend to decrease due to presence of natural fractures associated with fault zones without impacting reservoir pressures, suggesting that regions with high reservoir pressures and low breakdown pressures are the best areas for development. The second part of this study focused on understanding the cause and effect of parent-child interactions, specifically the impact of modern well completions (2018 or newer) near vintage completions (2010-2014), to assess the impact on well performance for both completion types. Parent-Child interactions analyzed in the field using breakdown pressures and production trends suggests both intra-bench (Haynesville-Haynesville and Bossier-Bossier) and inter-bench (Haynesville-Bossier) communication resulting in as much as ∼5-15% production uplift in older vintage parent wells without impacting performance on child wells. This is a unique behavior observed in the Haynesville Basin contrary to the parent-child effects generally observed in unconventional plays resulting in performance degradation. We suggest that production uplift on older well vintages occur due to 1) new stimulated rock volume created near the parent wellbore in case of intra-bench interactions, and 2) reservoir re-pressurization due to child well completion in case of inter-bench and wider spaced intra-bench interactions. In the former case, fractures from parent and child producers in the same formation may grow together forming integrated networks to stimulate a larger rock volume and drain additional gas from the under-stimulated parent well without impacting the performance of the child well. In the latter case, it is unlikely that parent and child fractures become connected, and therefore increased productivity in the parent wells is likely the result of elevated pore pressures. The latter case phenomenon is the possible explanation of inter-bench communication between Haynesville and Bossier formations and intra-bench communication observed at wider spacing (3000-4000 feet). We also observed that the uplift in the vintage parent wells increases as a function of distance from the child well suggesting strong communication at lower distances. Interpreting under-utilized datasets in unconventional domain (breakdown pressures, seismic velocities, etc.) and integrating it with fundamental geoscience interpretation has been a key driver in this approach. Observations discussed in this paper can help optimize our development plans in terms of 1) correctly sequencing and down-spacing the wells to capture the additional value from the under-stimulated vintage completions, and 2) incorporating the production uplift in pre-drill and post-drill well economic analysis. Identifying such opportunities and integrating them with our development strategy can help optimize development plans and maximize value.