Pore Volume Ratio Research Articles

Evaluating the surface relaxivity and movable fluid of low-permeability sandstones based on low-field nuclear magnetic resonance

Comprehensive characterization of pore structure and fluid distribution is beneficial for efficiently exploring and developing low-permeability sandstone reservoirs. As a conversion parameter, the surface relaxivity is significant for characterizing the pore structure of porous media and evaluating fluid mobility. The surface relaxivity indicates the strength of the interaction between the fluid and the solid during the relaxation process. This paper conducts mercury intrusion porosimetry, low-temperature nitrogen adsorption, and nuclear magnetic resonance-centrifugation experiments on low-permeability sandstones, providing insight into the evolution of pore size and water content distribution. Combining mercury intrusion porosimetry with nuclear magnetic resonance, the surface relaxivity of samples is measured to be 9.57–23.79 μm/s. The surface relaxivity ranges from 0.70 to 3.72 μm/s utilizing low-temperature nitrogen adsorption and nuclear magnetic resonance. Based on the movable water saturation through the critical radius, the calculated surface relaxivities using two methods are compared. The result indicates that surface relaxivity determined by low-temperature nitrogen adsorption is smaller than that obtained through mercury intrusion porosimetry. This is attributed to overestimating the ratio of pore surface and pore volume in the low-temperature nitrogen adsorption, which is difficult to capture information about macropores. Conversely, the similar principle between mercury intrusion porosimetry and centrifugation leads to consistent movable water saturation, minimizing discrepancies in evaluating surface relaxivity. Therefore, the surface relaxivity determined by mercury intrusion porosimetry-nuclear magnetic resonance is more suitable for characterizing the pore structure and fluid mobility of low-permeability sandstones. In addition, the ink-bottle effect retains water in the macropore during centrifugation experiments.

Study on the mechanical behavior of millennium-ancient bricks based on microscopic characteristics

The wide performance variation and inability for destructive testing make accurately determining ancient brick mechanical properties crucial for assessing structural safety in ancient masonry. This paper uses multiscale modeling with microscopic finite element analysis to quantitatively assess ancient brick macroscopic stress–strain relationship and compressive strength based on microstructural characteristics. The basic parameters such as porosity, pore size distribution, mineral composition and volume ratio, and microstructure characteristics of ancient bricks were obtained by corresponding methods. The Mori-Tanaka homogenization theory was applied to derive a three-phase equivalent brick matrix using elastic moduli and Poisson’s ratios of quartz, kaolinite, and montmorillonite at the microscale. The Representative Volume Element model with pores was created based on this matrix and pores, integrating Drucker-Prager plastic damage for finite element analysis of ancient brick mechanical behavior. The results indicate that stress–strain curves from the multi-scale micromechanics model resemble macroscopic experimental curves and maintain consistent peak strength. This shows that combining microscopic testing with finite element simulation for analyzing the mechanical properties of ancient bricks is feasible, providing a new non-destructive means of obtaining these properties.

Hydrothermal preparation of cotton-based rGO/N-doped porous carbon as electrode materials of supercapacitors

Porous carbon electrode materials are commonly used in supercapacitors due to their inexpensive raw materials, simple processing, and low pollution, aligning with the vision for green energy storage. Consequently, there is a current trend to discover porous carbon electrode materials with superior electrochemical properties. To enhance the pore volume ratio and electrochemical performance of porous carbon materials, this study proposes a hydrothermal method to pretreat the raw materials, facilitating the doping of nitrogen from urea. Moreover, graphene is introduced for its excellent conductivity, which can further improve the electrochemical properties of the material. We found a new one-step reduction Graphene Oxide (rGO)and the doping of nitrogen (N) elements were optimized by hydrothermal method, the wettability and pseudo-capacitance performance of the material are improved, and HTPC-700 shows a very excellent specific capacitance, its specific capacitance reaches 600 F g−1 at a current density of 0.5 A g−1, and it even reaches 260 F g−1 at a current density of 1 A g−1. Meanwhile the power density and energy density are respectively 74 W h kg−1 and 280 W kg−1. It also exhibits a remarkable capacitance retention rate of over 98.7 % after 5000 cycles at a current density of 1 A g−1. Additionally, it demonstrates a rich ant nest-like pore structure and good specific surface area of 2427 m2/g, and a large pore volume of 1.09 cm3/g after carbonization and KOH activation. This study offers a novel doping method and provides a unique perspective for the development of porous carbon electrodes.

Study on water-salt phase transition of saline soils during freezing

As the temperature decreases, when the freezing temperature is reached, the solution in the pores of saline soil undergoes ice crystallization and salt crystallization phenomena. Theoretical and experimental studies have been carried out in order to investigate the behaviour of water-salt phase transitions within the pores of saline soils. Firstly, the theoretical expression for the initial crystallization radius is given from the thermodynamic theory by considering the interphase chemical potential equilibrium and the Young-Laplace equation, and the relationship between the initial crystallization radius and temperature as well as the initial salt content is analyzed. Then, a theoretical model to predict the pore solution content and crystal content was developed in conjunction with the Van Genuchten soil-water characteristic curve model, and the water-salt phase transition behaviour of saline soils was analyzed by numerical calculations. Finally, the validity of the theoretical model was verified by a saline soil freezing test. The results show that the water-salt phase transition behaviour of the solution within the pores of saline soils is affected by temperature and initial salt content, and the water-salt phase transition behaviour mainly occurs at the early stage of freezing. Salt lowers the freezing temperature of the soil; the higher the salt content, the lower the freezing temperature, and the presence of salt inhibits the growth of ice crystals. As the temperature decreases, the precipitation of ice salt crystals during the phase transition of the soil pore solution reduces the soil porosity and decreases the channels for ion migration, resulting in a gradual increase in the soil pore volume ratio.

Porosity Characteristics of Coal Seams and the Control Mechanisms of Coal Petrology in the Xishanyao Formation in the Western Part of the Southern Junggar Basin

The porosity characteristics of coal seams serve as a pivotal factor in assessing the development potential of coalbed methane (CBM) resources, significantly influencing the adsorption and permeability capabilities of coal reservoirs, as well as the accumulation, entrapment, and preservation of CBM. In this study, we focused on the coal seams of the Xishanyao Formation in the western part of the southern Junggar Basin (NW China). By leveraging the complementarity of nuclear magnetic resonance (NMR), low-temperature liquid nitrogen experiments, and high-pressure mercury intrusion porosimetry (MIP) in spatial exploration range and precision, we conducted a comprehensive analysis to achieve a fine description of porosity characteristics. Furthermore, we explored the coal petrology factors controlling the pore characteristics of the Xishanyao Formation, aiming to provide geological evidence for the selection of favorable areas and the development potential evaluation of CBM in the study area. The results indicate the following: (1) The total pore volume of the coal samples is 6.318 × 10−3 cm3/g on average, and the micropore volume accounts for a relatively high proportion (averaging 44.17%), followed by the fine pores (averaging 39.41%). The average porosity is approximately 3.87%, indicating good gas storage and connectivity of the coal seams, albeit with some heterogeneity. The coal reservoir is dominated by micropores and fine pores with diameters less than 100 nm, and the pore structure is characterized by low pore volume and high pore area. (2) The pore structure is influenced by both the coalification degree and the coal maceral. Within the range of low coalification, porosity increases with the increase in coalification degree. Building upon this, an increase in the vitrinite content promotes the development of micropores and fine pores, while an increase in the inertinite content promotes the development of meso–macropores. The clay mineral content exhibits a negative correlation with the adsorption pore volume ratio and a positive correlation with the seepage pore volume ratio.

Reservoir characteristics and controlling factors of the middle–high maturity multiple lithofacies reservoirs of the Lianggaoshan Formation shale strata in the northeastern Sichuan basin, China

The Lianggaoshan Formation, which is located in the northeastern part of the Sichuan Basin, is an important shale oil producer. However, due to the effects of complex petrography, a wide range of maturity, and lower organic matter (OM) content in comparison to other areas, the pore characteristics of different lithofacies are unclear, which severely limits exploration and development. Therefore, by using geochemical, petrological and pore structure characterization experiments, this study thoroughly examines the pore properties of several lithofacies in the Lianggaoshan Formation in Northeast Sichuan. The deposits in the study area are OM-rich laminated argillaceous shale (ORLAS), silty mudstone (SM), OM-low laminated siliceous shale (OLLSS), organic-laminated argillaceous shale (OLLAS), OM-low bedded shale (OLBMS), and (fine) siltstone (FS). With higher porosity and macropore + microfracture volume ratio, ORLAS and OLLSS have better reservoir qualities than the other lithologies, while the reservoir properties of SM and FS are the worst. Hydrocarbon generation and diagenesis affecting pore development include thermal maturation of OM, mechanical compaction, dissolution, and cementation. The porosity and medium–large scale pore volume ratio show a tendency to increase and then decrease with maturity, reaching their highest values at an Eq range of (Ro) = ∼1.6%. Dissolution greatly contributes to pore development. The pore space is primarily sealed by cementation and compaction, which is most evident in SM and FS. In addition to thermal maturity, factors affecting the reservoir properties include clay minerals, siliceous minerals, and total organic carbon (TOC). Clay minerals and OM often form OM–clay mineral complexes, which can promote hydrocarbon generation and pore enlargement through interaction. The properties of the reservoir significantly improved when TOC and clay contents increased. However, the lithology of the study area, which contains a significant concentration of siliceous minerals, is unfavorable to reservoir properties.

Facile synthesis of TiO2-carbon composite doped nitrogen for efficient photodegradation of noxious methylene blue dye.

The present work shows that the degrading ability of TiO2 is significantly improved when exposed to light, particularly in relation to the organic dye methylene blue (MB), following the introduction of a carbon framework through sol-hydrothermal synthesis approach. The newly prepared TiO2-C@N composite had the ability to function as both an adsorbent and a photocatalyst to eliminate MB from contaminated wastewater. The outcomes show the removal efficiency of MB amounts to 99.87% upon the application of UV radiation, which is much higher than the rate achieved under dark conditions (28.9%). As ascertained by the kinetic study, the degradation of methylene blue (MB) under UV light through photocatalysis using the TiO2-C@N photocatalyst conformed to the widely recognized pseudo-first order (PFO) model. TiO2-C@N photocatalyst showed outstanding reliability and reusability, maintaining consistent degradation efficiency over five consecutive cycles without any obvious decline. The materials were characterized by XRD, XPS, FE-SEM, EDS, and N2 adsorption-desorption measurements. Nanometer-sized particles, a unique surface dominance, high surface area, large pore volume ratios, low band gap, high oxygen vacancies, increased pollution absorptivity, and reduced electron-hole pair recombination characterize the monolithic TiO2-C@N photocatalyst over TiO2. These unique features render TiO2-C@N a promising catalyst in effectively breaking down noxious MB organic pollutants through photodegradation.

Tofukasu-derived biochar with interconnected and hierarchical pores for high efficient removal of Cr (VI)

Herein, we report the synthesis of interconnected hierarchical pore biochar (HTB) via an ice-templating strategy using bio-waste (tofukasu). The abundance of N- and O-containing functional groups in tofukasu makes it easy to form hydrogen bonds with water molecules and water clusters, resulting in nano-micro structures like ice clusters and snow crystals during freezing process. More importantly, tofukasu will be squeezed by micron-scale snow crystals to form coiled sheet-like structures, and its surface and interior will be affected by needle-like ice nanocrystals from several nanometers to tens of nanometers to form transverse groove needles and mesopores. The ice crystals are then removed by sublimation with tofukasu, leaving the interconnected pore structure intact. Therefore, the ice template synthesis strategy endowed the interconnected hierarchical pore structure of HTB with a large specific surface area (SBET, 733 m2⋅g−1) and hierarchical porosity (30.30% for mesopores/total pore volume ratio), which is significantly higher than the normal dry treated tofukasu biochar (TB), which had a SBET of 436 m2⋅g−1 and contained 1.53% mesopores. In addition, the sheet-like structure with interconnected pores of HTB favors high exposure of active sites (N- and O-containing functional groups), and a fast electron transport rate. As a result, HTB had an excellent adsorption capacity of 159.65 mg⋅g−1, which is 4.7 times that of typical block biochar of TB (33.89 mg⋅g−1) according to Langmuir model. Electrochemical characterization, FTIR and XPS analysis showed that the mechanism of Cr(VI) removal by HTB included electrostatic attraction, pore filling, reduction and surface complexation.Graphical

Characteristics and Influence Factors of Natural Desorption in Coal Bodies from Fukang Mining Area, Xinjiang, China.

Coal body desorption characteristics are one of the key factors that influence the development of coalbed methane (CBM). In this study, 91 coal core samples from 11 CBM wells in the Fukang mining area were collected from Xinjiang, China, and the coal quality, high-pressure mercury compression, gas content, and natural desorption characteristics measurements were launched. With the detailed analyses of the differences in cumulative desorption volume, desorption ratio, and on-site average desorption rate for the coal samples with different body structures and macrolithotypes, the influence of the maximum reflectance of vitrinite, microscopic coal rock composition, and coal quality and pore characteristics on CBM desorption characteristics were discussed. The results showed that the cumulative desorption volume, desorption ratio, and desorption rate of cataclastic structure-bright coal are higher than those of primary structure-semibright coal. With the increase of RO,max and vitrinite content, the adsorption capacity of coal increases, and the increased methane concentration difference during desorption leads to an increase in cumulative desorption volume and on-site average desorption rate. The higher contents of moisture and ash yield would occupy the adsorption sites and hinder gas diffusion, which would decrease the desorption of coalbed methane. The greater porosity/pore volume ratio of medium and large pores can enhance the connectivity of pores, which increases the desorption ratio and the average desorption rate, while the higher micropore porosity/pore volume ratio can increase the gas adsorption space and the cumulative desorption volume. The pore characteristics have the most significant effect on the cumulative desorption volume and desorption ratio. The results of the study can help guide coal mine gas management and CBM development from middle-and low-rank coal reservoirs in Xinjiang.

Research Note: Three-dimensional microstructural basis for chicken eggshell translucency

Eggshell translucency, an externally observable feature, can influence consumer purchase intentions. The eggshell quality often deteriorates in aging laying hens, leading to increased eggshell translucency. Eggs exchange water vapor through the pores. It is commonly believed that the moisture remaining in the mastoid space contributes to translucent egg formation. However, the precise mechanisms underlying eggshell translucency require further structural investigations. This study aimed to explore the 3-dimensional microstructure of eggshells using micro-computed tomography (micro-CT) to provide insights into the microstructural basis of eggshell translucency. The results revealed that the ratio of pore volume to mastoid space volume was significantly higher in the high-translucency (TH) group than that in the low-translucency (TL) group (P < 0.01); however, the ratio of mastoid space to eggshell volume showed no significant difference. Additionally, measurements of the individual pore morphological features showed that the roundness of the pores in the TH group was significantly higher than that in the TL group, whereas the flatness of the pores in the TH group was significantly lower (P=0.01). Eggshell porosity directly reflects the water vapor exchange capacity of eggshells, with the TL group exhibiting significantly higher eggshell porosity compared to the TH group (P=0.02). In conclusion, based on observations of the 3-dimensional microstructure of eggshells, this study elucidated how the volume and morphological characteristics of pores influence the water vapor exchange capacity of eggshells, resulting in eggshell translucency.

Radon exhalation characteristics after pyrolysis of long flame coal

Coal pyrolysis is a important method for classifying and utilizing coal resources and contributes to enhanced comprehensive resource utilization. However, In high-temperature areas such as coal pyrolysis, there is an abnormal phenomenon release of radioactive gas radon, understanding the relationship between temperature and radon exhalation characteristics, as well as the underlying mechanisms, holds great importance for assessing radon pollution in mining areas. After coal undergoes pyrolysis under high temperature conditions, its material composition, pore structure, water content, and other properties have changed. The pyrolysis products in different atmosphere environments have differences, and the characteristics of radon emission are also different. To address this, the present study conducted coal pyrolysis experiments in both aerobic and anaerobic environments, using long flame coal sourced from Yulin, China. The radon release concentration of the pyrolysis products was measured. The research findings indicate that during pyrolysis at elevated temperatures, the ratio of coal mass loss is constantly increasing. High temperatures promote the development of pores and fissures, and significant changes in coal properties at temperature thresholds (300 °C and 500 °C). The specific surface area, pore volume, and fracture ratio all display substantial increases, and the amplitude of change is greater under aerobic conditions. The fractal dimension of total pores and macropores shows continuous growth, while the specific surface area, pore volume, and fracture ratio exhibit a strong negative correlation with the radon emission rate of pyrolysis products. The expansion and penetration of pores and cracks, along with the release of a substantial amount of pyrolysis gas, accelerate the transformation, migration, and exhalation of radon, resulting in a negative correlation between the heat treatment temperature and the radon release rate of pyrolysis products. Under aerobic conditions, the radon release rate of pyrolysis products decreases more significantly.

Investigation of internal damage evolution in gneiss considering water softening

In soft rock tunnels, there are often large deformations during construction, especially when the groundwater seepage and softens the surrounding rock. For achieving the purpose of studying the softening effect of water immersion on strength and stability of surrounding rock, 15 rock samples were selected for physical and mechanical tests under 5 conditions: natural state and free immersion for 1, 3, 6, and 9 months, and nuclear magnetic resonance technology(NMR) was also adopted to test the internal pore structure of specimens with different immersion durations, thus the micro structure features of the gneiss, such as the NMR relaxation time T2 spectrum distribution, porosity, and pore volume ratio of different pore sizes under water softening were then obtained. The NMR results shows that the longer the free immersion duration of the rock sample, the greater the porosity; at the same time, the number of micropores in the rock gradually decreases under the interaction of water and rock, and the mesopores increase slightly first and then decrease all the time. The number of macropores is gradually increasing. When the immersion duration is 6 months, the number of macropores begins to increase significantly, and the mechanical properties of the specimens begin to drop significantly. By 9 months, the proportion of macropores in the rock has reached 57.6%. The results showed that the number growth of macropores is the root cause of the macroscopic failure of rock sample. The study results have significance for on-site construction in water-rich areas.

Facile synthesis of nanoscale tantalum powder by electro-deoxidation of Ta2O5

We report a facile approach for the synthesis of nanoscale tantalum powder through the electro-deoxidation of Ta2O5 cathode in molten Na3AlF6-K3AlF6-AlF3. The cathodic process begins with a solid-liquid reaction between Ta2O5 and the electrolyte, resulting in the formation of MxTaO2+xF1-x (M = Na, K) intermediates, which are then electrochemically reduced to tantalum directly. We developed a Ta2O5 cathode with a new porous structure, which contains interconnected microporous, mesoporous and macroporous structures, possessing properties such as high surface area, high pore volume ratios, and excellent accessibility to active sites. This novel cathodic pore structure material enabled the formation of uniform-sized MxTaO2+xF1-x particles with a regular cubic morphology by providing abundant nucleation sites and promoting uniform growth of intermediate. The electrochemical decomposition of these particles and the nucleation, growth mechanisms of tantalum product were also investigated. Our study demonstrates the rational design and synthesis of hierarchically porous cathode materials can facilitate the controllable synthesis of nanoscale metal powders by the FFC process, and may open up new opportunities for the development of other materials with desired morphology and particle size.

Numerical simulation of coated proppant transport and placement in hydraulic fractures based on CFD-DEM

Channel fracturing technology is designed to form fractures supported by non-uniform pillar proppants. Non-cured adhesive resin-coated proppant gradually becomes viscous after immersion and agglomerates during transportation. The pillars are stable after the fracture is closed. They not only maintain a certain compressive strength but also maintain long-term conductivity. Currently, there are few evaluations of coated proppant migration. Based on CFD-DEM method, a two-phase flow coupling model considering the adhesive contact force of coated proppant particles is established to study the cementation characteristics of coated proppant during transportation. The transportation mechanism of coated proppant are revealed by numerical calculation analysis. The results show that different from the conventional proppant, the migration process of the coated proppant is divided into four stages (1) the softening of the proppant contact; (2) the paving of the proppant agglomeration; (3) proppant pillars growth along fracture height; and (4) proppant pillars growth along fracture length. We have completed a preliminary geometric characteristics evaluation of sand bank formed by coated proppant by evaluating the pore volume ratio (the ratio of void volume between pillars to the sand bank volume) under various parameters. This evaluation offers some theoretical guidance for the optimization of channel fracturing proppant injection parameters.

Impacts of liquid phase distribution on the effective thermal conductivity of closed-cell thermal insulation

This paper proposes a multiscale effective thermal conductivity model combined with liquid phase distribution to explore in detail the influence of the internal structure of closed-cell thermal insulation on the thermal behavior in the presence of moisture. By simulating the liquid phase distribution in the cracks between the insulation cell skeleton and combining it with the representative elementary volume (REV) scale and macroscopic scale thermal conductivity models, the correlations between the structural parameters, saturation, and effective thermal conductivity of phenolic thermal insulation are analyzed. A critical saturation point is proposed for the first time, and the related impact factors are discussed. For the heat and moisture transfer in porous media, the larger the critical saturation, the better the insulation performance. Based on the newly developed improved effective thermal conductivity model, nine groups of phenolic samples with different structural parameters were investigated to compare the impact of porosity, closed-open pore volume ratio, relative deviation ratio, contact angle, and closed-pore diameter on the effective thermal conductivity. Simulation results indicate that the influence of the liquid phase distribution is mainly reflected at low saturation at the REV scale; at the macroscale, the influence of the liquid phase distribution is significantly reduced.

Pore Structure Evolution in Sandstone of Underground Gas Storage during Cyclic Injection and Production Based on Nuclear Magnetic Resonance Technology

The underground gas storage (UGS) in depleted sandstone reservoirs forms the largest proportion of the UGS market in China. Multiple cycles of natural gas injection and production in the sandstone cause the rapid increase and drawdown of pore pressure, which may induce damage to the rock skeleton structure, and cause complex fluid flow paths in the sandstone reservoir. In this paper, transverse relaxation time (T2), nuclear magnetism resonance imaging, and high-pressure mercury intrusion analysis are combined to evaluate the variation in pore structure of medium-grained sandstone. The results show that cyclic injection and production of fluid leads to a slight increase in total pore volume, indicating that weak damage to rocks occurs. The T2 spectrum at the low pore pressure (10 MPa) and high pore pressure (25 MPa) both show that the shrinkage of the medium-size pores occurs after multiple cycles of injection and production. The pore volume of large-size pores was not highly correlated with the number of cycles. With the increase in pore pressure, the pore volume ratio under high pore pressure increased with the number of cycles, while it fluctuated strongly under low pore pressure.

Design of hierarchically porous carbon frameworks for enhanced CO2 capture performance

To reduce the environmental impact of CO2, CO2 capture has become an area of research interest. Hierarchically porous materials have been certified as efficiency CO2 capture adsorbents. This work is aimed to construct hierarchically porous carbon frameworks (CPI-TPUs) with enhanced CO2 capture performance. CPI-TPUs are derived from polyimide (PI)/thermoplastic polyurethane (TPU) composite aerogels (PI-TPUs) with mesopores and macropores. Accordingly, the obtained CPI-TPU2 exhibits an improved CO2 uptake capacity (2.21 mmol/g, 298 K) compared to the pure CPI and PI-TPUs due to the synergistic effect of hierarchically pores, higher specific area and electron-rich heteroatoms. Specially, CPI-TPUs with pore volume ratio of mesopores/macropores to total pores in a range of 6–21 show high CO2 uptake performance. These CPI-TPUs with high CO2 adsorption capacities and suitable isosteric adsorption heats (Qst) are promising CO2 adsorbents.

Characteristics of Gas Seepage and Pore Structure Response in CO2-ECBM Process of Low Permeability Coal Seam

CO2-ECBM is a method of enhanced coalbed methane extraction followed by cutting greenhouse gas emissions and new energy development. In order to reveal the characteristics of gas flow in porous media and the pore structure response characteristics of coal rocks, the experiments were carried out to simulate the process of CO2 displacement of N2 at a buried depth of 900 m, including monitoring the changes in gas permeability and strain of coal samples along with a comparison of the pore structure of low-temperature liquid nitrogen adsorption on coal samples both before and after displacement were both done. The findings of the experiment are listed below. The N2 permeability of the LiuZhuang sample ranges from 0.0008mD to 0.0014mD, whereas the permeability of QiDong is around 0.0003mD. With an increase in gas injection duration and an expansion of the coal matrix for N2 adsorption, the permeability steadily decreases. The efficient stress compression of the coal pore fracture structure during sample preparation and testing avoids the visible fracture region, which results in poor permeability. The displacement stages of CO2 can be divided into three phases. Free nitrogen flows from the end of the position and the permeability diminishes during the phase of free nitrogen. When CO2 is introduced into the penetration stage, the permeability tends to rise, however when there is no penetration, the permeability test values are frequently low. During the CO2 steady displacement phase, gas permeability gradually declines. Axial and radial strains are progressively raised during the initial stage of the CO2 injection whereas they are gradually reduced during the initial stage of the N2 injection. While CO2 is continuously supplied through the coal body stage, there are modest axial and radial strain changes. The axial and radial stresses are stabilized by the CO2 displacement. The overall pore volume of the coal significantly rises following the displacement. The increase part of the pore volume is primarily focused on the pore of absorption and filling (aperture &lt; 10nm), whereas the decreased part is mainly concentrated in the diffusion pore of the Fick type and the permeability part (aperture &gt; 50nm). The increased in pore volume ratio surface area is centered mostly in the fill pore region (aperture 10 nm) and is four times greater than it was before the displacement. The CO2 injection exerts an expansion impact on the adsorptionfilled and diffusion pores during the CO2-ECBM process, whereas the compression effect on the percolation pores results in a reduction in permeability.

Estimation of effective thermal conductivity in open-cell foam with hierarchical pore structure using lattice Boltzmann method

• Hierarchical pore structure is built in open-cell foam by an artificial algorithm. • Effective thermal conductivity (ETC) was calculated by lattice Boltzmann method. • Effects of hierarchical pore structure on ETC were investigated. • ETC correlation for open-cell foam with hierarchical pore structure is derived. Effective thermal conductivity in open-cell foam with hierarchical pore structure was estimated using lattice Boltzmann method. A new structure algorithm was proposed to reconstruct hierarchical pore structure in open-cell foam. In order to elucidate the heat transfer characteristics in hierarchical pore structure, the effect of structure parameters, namely the hierarchical pore size ratio ( d 2 / d 1 ), the hierarchical pore volume ratio ( V 2 / V 1 ), and temperature on the effective thermal conductivity was investigated. These results indicated that hierarchical pore structure is unfavorable to the effective thermal conductivity in open-cell foam for the heat conduction process. At high temperatures ( T ave =450-1650 K ), however, the effective thermal conductivity in hierarchical pore structure is higher than that in uniform pore structure considering heat radiation. Furthermore, for the heat conduction process, a correlation of the effective thermal conductivity related to open-cell foam with hierarchical pore structure was proposed and validated by available experimental data.

Lattice Boltzmann study on the effect of hierarchical pore structure on fluid flow and coke formation characteristics in open-cell foam for dry reforming of methane

Dry reforming of methane (DRM) is one of the feasible strategies for carbon capture and utilization. However, the DRM process has a high tendency toward carbon deposition, which is restricted to industrial applications. In order to further improve coke formation resistance, open-cell foam with hierarchical pore structure was investigated. An artificial algorithm was adopted to construct a hierarchical pore structure in open-cell foam. Based on a 3-D lattice Boltzmann model, this work explored the effect of two hierarchical pore structure parameters on the fluid flow and coke formation characteristics in open-cell foam, which are hierarchical pore volume ratio (V2/V1) and hierarchical pore size ratio (d2/d1). The results indicated that increasing V2/V1 and d2/d1 can significantly promote permeability. Under the restriction ofV2/V1 = 4, from d2/d1 = 1 to 4, the coke formation rate decreases by approximately 57.49 %. These findings provide a theoretical basis and technical guidance for designing and developing open-cell foam reactors.