Water Pore Research Articles

The Seepage Mechanism of Micro Remaining Oil During Cyclic Waterflooding in Low-permeability Reservoir

To explore the flow mechanism of micro-remaining oil during cyclic waterflooding in low-permeability reservoir, the displacement effect of micro-remaining oil under conventional waterflooding and different rounds of cyclic waterflooding was investigated by using a micro-visual displacement experiment based on microfluidics model. The produced ratio of different types of micro remaining oil during cyclic waterflooding was quantified, and major types of micro remaining oils that can be applied effectively during cyclic waterflooding were analyzed. Moreover, the flow mechanism of micro remaining oil during cyclic waterflooding was investigated. Research results demonstrated that clustering type remaining oil and columnar type remaining oil were major types that were applied during cyclic waterflooding. After three rounds of cyclic waterflooding, clustering-type remaining oil decreased by 2.50% on average, and columnar-type remaining oil decreased by 0.81% on average. The major mechanism of cyclic waterflooding is introduced as follows: at intervals of cyclic waterflooding, clustering type remaining oil and columnar type remaining oil exchange with water in pores, throats, and spaces between big and small pores due to the fluctuation of pressure field and effect of capillary force. As a result, oil and water redistribute. Clustering-type remaining oil and columnar-type remaining oil become movable oils.

Short‐term length change measurements and sorption isotherms for AAC compared to OPC

AbstractThe interaction of adsorbed water with the microstructure of cementitious materials leads to effects on macroscopic properties. However, precise quantitative correlation of adsorbed water with short‐term changes in macroscopic properties, such as dimensional changes, remains a challenge. We compare recent results from precise dual‐microscope‐based short‐term length change measurements and discuss differences in length‐change isotherms and adsorption isotherms arising from various cement types. Water vapor adsorption happens already at very low humidity in the interlayer space of the C‐S‐H gel. Adsorption and desorption on cement surfaces due to changing relative humidity induces strong forces in the cement gel, leading to detectable changes in dimensional stability for the hardened material. A significant hysteresis in the water desorption isotherm is often accompanied by hysteresis in dimensional change as well. For precise length change measurements, an optical method for tracking surface patterns on thin cement slices was applied. Short‐term length change results are compared to corresponding water vapor sorption isotherms and pore size measurements. Hypotheses and conclusions regarding microstructural changes and shrinkage mechanisms are discussed in order to understand the experimental data.

Pressure infiltration behavior and fluid loss of bentonite slurry: a comparative study of two bentonite slurries

Bentonite slurry is frequently used to temporarily stabilize the excavation for slurry tunnel boring machines (TBMs) driving in permeable soils, such as sand and gravel. In this study, two types of bentonite slurries (BS1 and BS2) were subjected to a series of infiltration column tests and modified fluid-loss tests under various pressure levels. Monitoring of water discharge and pore pressures at different depths of the sand bed enabled the identification of two effective sealing patterns during infiltration: the formation of a filter cake and rheological blocking. BS1 exhibited a tendency to form a filter cake, which played a vital role in effectively transferring the applied pressure to the underlying soil skeleton. The application of higher pressure facilitated the rapid formation of a filter cake, resulting in a shorter time span for slurry invasion and minimizing fluid loss. On the other hand, rheological blocking was dominant when using BS2, and the maximum infiltration distance was found to linearly increase with the applied pressure. A comparison between the measurement and a simple prediction model derived from Darcy's law revealed an overestimation of the infiltration distance during slurry invasion. Furthermore, based on the modified fluid-loss test, higher pressure was found to densify the filter cake and result in lower hydraulic conductivity.

Puncturing lipid membranes: onset of pore formation and the role of hydrogen bonding in the presence of flavonoids

Products of lipid peroxidation induce detrimental structural changes in cell membranes, such as the formation of water pores, which occur in the presence of lipids with partially oxidized chains. However, the influence of another class of products, dicarboxylic acids, is still unclear. These products have greater mobility in the lipid bilayer, which enables their aggregation and the formation of favorable sites for the appearance of pores. Therefore, dodecanedioic acid (DDA) was selected as a model product. Additionally, the influence of several structurally different flavonoids on DDA aggregation via formation of hydrogen bonds with carboxyl groups was investigated. The molecular dynamics of DDA in DOPC lipid bilayer revealed the formation of aggregates extending over the hydrophobic region of the bilayer and increasing its polarity. Consequently, water penetration and the appearance of water wires was observed, representing a new step in the mechanism of pore formation. Furthermore, DDA molecules were found to interact with lipid polar groups, causing them to be buried in the bilayer. The addition of flavonoids to the system disrupted aggregate formation, resulting in the displacement of DDA molecules from the center of the bilayer. The placement of DDA and flavonoids in the lipid bilayer was confirmed by small-angle X-ray scattering. Atomic force microscopy and electron paramagnetic resonance were used to characterize the structural properties. The presence of DDA increased bilayer roughness and decreased the ordering of lipid chains, confirming its detrimental effects on the membrane surface, while flavonoids were found to reduce or reverse these changes.

Transient of flow regimes and slip boundary analysis of water and gas in nano clay pores

ABSTRACT Nanoscale two-phase flow is important during shale gas production. In this work, molecular dynamics simulations are employed to investigate fluid flow regimes of water and methane under different pressure gradients inside the nanoscale slit pores. The illite mineral is selected to model the clay pores based on the Small-Angle X-ray Diffraction (SAXD) experiment. The different flow regimes of gas-water two-phase are visualised and the structures are analysed. As the driving pressure gradient increases, it is observed that the two-phase flow in the slit undergoes transitions from intermittent flow to a transition stage between intermittent flow and annular flow, and finally fully converts to annular flow. The slip conditions during the two-phase flow on the hydrophilic illite surface are investigated. We found that the negative slip length stays around 0.25 nm within the range of practical production pressure gradients, which can be used for accurate production prediction. This work provides detailed insights into the nanoscale water and gas two-flow inside the clay nanopores during shale gas exploration.

The Chemical Compatibility of Sand–Attapulgite Cut-Off Walls for Landfills

Soil–bentonite cut-off walls have been widely used to control landfill pollution but they do not have good chemical compatibility with landfill leachate. Attapulgite can be substituted for bentonite in landfill cut-off walls. However, little is known about the chemical compatibility of attapulgite cut-off walls and leachate. This study experimentally investigated the chemical compatibility of attapulgite cut-off wall specimens with organic and inorganic contaminants and found that a sand–attapulgite cut-off wall has good chemical compatibility with organic contaminants. A CaCl2 solution was used to represent inorganic contaminants, and chemical oxygen demand (COD) was used as an indicator of organic content. The hydraulic conductivity of the cut-off wall initially decreased and then increased to become approximately constant as Ca2+ concentration increased. Changes in COD concentration were divided into a decreasing stage (0–10,000 mg/L) and a constant stage (10,000–40,000 mg/L). The increase or decrease in hydraulic conductivity was by no more than one order of magnitude. The increase in the hydraulic conductivity of the sand–attapulgite cut-off wall is explained in terms of bound water content and pore structure. An increase in Ca2+ concentration decreased the bound water content of the cut-off wall while the CaCl2 solution increased macropore and mesopore volume and decreased small pore volume in the sand–attapulgite cut-off wall. The purpose of this study was to elucidate the chemical compatibility of a sand–attapulgite cut-off wall with organic and inorganic contaminants and to increase the understanding of the interactions between the cut-off wall and the contaminants. The results of this research are informative for improving the application, design, and construction of sand–attapulgite cut-off walls.

Constraining the major pathways of vanadium incorporation into sediments underlying natural sulfidic waters

Vanadium (V) is a redox-sensitive trace metal. Interconversion between different vanadium species (e.g., VIII, VIV, VV) occurs rapidly in association with changes in redox conditions in natural environments. Different vanadium species exhibit variable geochemical behavior that impacts if and how they are sequestered into sediments, which makes vanadium a useful proxy for ancient ocean redox conditions. However, we still lack constraints on how different dissolved vanadium sink pathways impact distributions of vanadium in water column, pore waters, and sediments, especially in natural sulfidic settings. In the present study, we combined field and experimental data to constrain the major scavenging processes that influence the partitioning of vanadium between aqueous and solid phases to provide an improved picture of vanadium geochemical cycling under anoxic-sulfidic conditions. We find that in the sulfidic bottom waters and sediment pore waters of the Chesapeake Bay, vanadium concentrations are correlated with manganese (Mn) concentrations in both aqueous and solid phases. Our experimental results support our interpretation that elevated concentrations of vanadium in anoxic-sulfidic waters result from the release of vanadium due to desorption from and/or dissolution of Mn oxides in anoxic/sulfidic waters. While sorption of vanadium results in strongly adsorbed complexes on both Mn oxides and pyrite surfaces, vanadium preferentially sorbs to Mn oxides rather than to pyrite. Thus, the impact of Mn oxides on vanadium geochemistry is greater than that imposed by scavenging via sorption on pyrite, although both processes should be considered. Mn oxides also have a greater impact on vanadium geochemistry than reductive formation of solid V(OH)3 by H2S. Sorption of vanadium is sensitive to pH conditions (especially in anoxic waters), moderately sensitive to ionic strength, and weakly sensitive to phosphate concentrations. In addition, our results show that as waters become more sulfidic, dissolved V/Mn molar ratios increase, whereas solid phase V/Mn molar ratios decrease, indicating that the V/Mn molar ratio can be used to trace redox changes. Finally, we investigate the V/Mn record of black shales that span the Proterozoic and Phanerozoic to show a framework of utilizing this proxy with applicability to identify changes in redox conditions associated with both oxygenation and anoxic events in ancient oceans.

Fabrication of high-performance MeI and HPEI assembled PES/CPES hollow fiber nanofiltration membranes with high positive charges for efficient removal of salt/heavy metal ions

Environmental protection and resource recovery require efficient separation of salts and heavy metal ions from wastewater. A new hollow fiber nanofiltration membrane (HFNM) with a highly positive charge was developed via Hyperbranched polyethyleneimine (HPEI) self-assembly and methyl iodide (MeI) quaternization on a polyethersulfone (PES) with carboxylic-PES (CPES) substrate. Effects of different layers on surface charge and roughness, wettability, and mechanical stability were evaluated. MgCl2 and ZnCl2 as representative of salts and heavy-metal ions, respectively, were used to investigate separating properties of the membranes in terms of feed temperature and concentrations, operating pressures, antifouling properties, and long-term stability. The relationship between salt/ions rejection and water flux, pore size, and surface positive charge degree was explained by comparing the structures and properties of the membranes. The 1wt.% HPEI and 0.5 wt.% GA solutions for 30 min crosslinking at pH of 11 and then 5 wt.% MeI solution could lead to the formation of the optimum membrane. Based on high hydrophilicity, low surface roughness, Donnan exclusion, and steric hindrance, the membrane could effectively exhibit superb rejection rates of Zn2+ (99.8 %), and Mg2+ (98.6 %), while showing high flux values (24.47 and 33.54 Lm−2h−1). The high flux rate (around 25.41 Lm−2h−1) during 4 cycles of regeneration, and high ions rejection (>98 %) were retained even after an 8-hour consistent operation. The prepared membrane, with high durability and structural stability, can introduce an effective solution for water purification from divalent ions.

Anisotropic molecular diffusion in confinement I: Transport of small particles in potential and density gradients

HypothesisDiffusion in confinement is an important fundamental problem with significant implications for applications of supported liquid phases. However, resolving the spatially dependent diffusion coefficient, parallel and perpendicular to interfaces, has been a standing issue. In the vicinity of interfaces, density fluctuations as a consequence of layering locally impose statistical drift, which impedes the analysis of spatially dependent diffusion coefficients even further. We hypothesise, that we can derive a model to spatially resolve interface-perpendicular diffusion coefficients based on local lifetime statistics with an extension to explicitly account for the effect of local drift using the Smoluchowski equation, that allows us to resolve anisotropic and spatially dependent diffusivity landscapes at interfaces. Methods and simulationsAn analytic relation between local crossing times in system slices and diffusivity as well as an explicit term for calculating drift-induced systematic errors is presented. The method is validated on Molecular Dynamics simulations of bulk water and applied to simulations of water in slit pores. FindingsAfter validation on bulk liquids, we clearly demonstrate the anisotropic nature of diffusion coefficients at interfaces. Significant spatial variations in the diffusivities correlate with interface-induced structuring but cannot be solely attributed to the drift induced by local density fluctuations.

Response of dissolved organic matter characteristics to nitrogen addition in a boreal peatland of Northeast China

Boreal peatlands, a crucial stock of dissolved organic matter (DOM), are susceptible to increased reactive nitrogen (N) inputs. However, the response of DOM characteristics to elevated N availability in these ecosystems is still obscure. Here, we investigated the seasonal variability of DOM quantity and characteristics in surface water and soil pore water after 5-year multi-level N addition (0, 3, 6, and 12 g N m−2 year−1) in a permafrost peatland of Northeast China. In this study, we used the excitation-emission matrix fluorescent spectroscopy combined with fluorescence regional integration, parallel factor analysis, and fluorescence parameters to decipher the effects of N addition on DOM composition, origin, and fate. Irrespective of N addition level, increased N availability reduced dissolved organic carbon concentrations in surface water and soil pore water. However, DOM characteristics are more responsive to N addition in soil pore water than in surface water. Nitrogen addition did not affect DOM composition in surface water, but altered the proportions of tyrosine-, tryptophan-, fulvic acid-, and humic-like DOM in soil pore water. Moreover, the changing trends of DOM composition were diverse during the growing season. In addition, compositional transformations of DOM did not change its biogenic signals, freshness, and humification in both surface water and soil pore water across the growing season. Our results suggest that increased N availability reduces DOM quantity and alters DOM chemical composition, which will improve our understanding of soil organic matter dynamics in boreal peatlands.

The effect of pore characteristics on the bonding properties of steam-cured concrete and GFRP bars

Steam cured concrete prefabricated components has the advantages of short construction period, less environmental pollution, convenient construction and low cost, and is widely used in high-speed railway projects. However, the changes of later strength, capillary water absorption and pore distribution led to the reduction of durability of steam-curing concrete and accelerated the damage speed of GFRP bars and bond performance between concrete and GFRP bars. In this study, the method of steam curing is adopted to simulate the damage of components caused by actual steam curing environment. The influence of pore characteristics on the bonding properties of steam cured concrete and GFRP steel bar is analyzed from both micro and macro perspectives. Analysis method combining pore characteristics with bonding strength. The test results showed that the hydration products of concrete were unaffected, but the density of the hydration products changed due to the steam curing. The porosity of the steam-cured concrete was much higher than that of the standard-cured concrete. The number of gel pores smaller than 20 nm accounted for 12.27% of the total number of pores on average, which was about twice the proportion of the gel pores of this size in the standard-cured concrete. The proportion of harmful voids with pore size of 50–200 nm and greater than 200 nm is higher than that of standard curing concrete. The bond strength of the steam-cured concrete and GFRP bars was 30% lower than that of the standard-cured concrete. With the change of the thickness of the concrete cover and the diameter of GFRP bars, the bond strength changed significantly. Based on the analysis of the test data, a predictive model of the bond strength deterioration for the steam-cured concrete and GFRP bars was established. The model fully accounted for influence factors such as the porosity, diameter, anchor length, and concrete strength.

An Experimental Approach to Investigating Quasi-Saturation Using Darcy’s Law

Recent trends in abnormal weather patterns leading to sudden and localized heavy rainfall have resulted in an increased frequency of surface landslides. As a result, there is a pressing need for improved prediction and early warning systems. This research focuses on understanding soil behavior under quasi-saturation and elucidating its relationship with pore water pressure and the hydraulic head. In the present study, a mathematical model is formulated to characterize the complex dynamics of quasi-saturation based on established principles. The model demonstrates the correlation between volumetric water content and pore water pressure, considering the influence of the hydraulic gradient. Through two comprehensive model tests, empirical data are generated that highlight the intricate factors influencing quasi-saturation. The findings of this study emphasize the complex interrelationship between volumetric water content, pore water pressure, and the hydraulic head. It is worth noting that under quasi-saturation conditions, the volumetric water content may stabilize over time, indicating an equilibrium between water flow rates driven by the hydraulic gradient and pore water pressure. The present study offers new insights into soil moisture dynamics and lays the foundation for advancements in landslide prediction and mitigation strategies.

Determining the residual service life of polymer-modified asphalt concrete pavement on road bridges

The object of research is the asphalt pavement of road bridges. Its residual period was assessed taking into account the joint effect of the ambient temperature and vehicles. It has been established that a set of negative factors affects the reduction of the service life (residual resource) of asphalt pavement on bridges. These include different modulus of elasticity of reinforced concrete base and asphalt pavement and the difference in coefficients of linear thermal expansion. As well as loads from the wheels of vehicles, temperature fluctuations, alternating freezing-thawing of water in pores and damaged places. It was found that one of the reasons for reducing the residual life of asphalt pavement on reinforced concrete road bridges is the insufficient study and use of polymers in order to adjust the properties of asphalt concrete. Taking into account the joint influence of temperature and transport in assessing the crack resistance of asphalt pavement on reinforced concrete road bridges would allow a more objective assessment of the residual life of such coatings and their service life. Arrangement of asphalt pavement with improved properties, due to polymeric latex, could increase its residual life. This, in turn, would lead to a reduction in costs for the repair and maintenance of not only asphalt pavement but also the road bridge as a whole

Obtaining biochar from rice husk and straw

This paper presents the results of research on obtaining biochar from agricultural plant waste such as rice husk and straw. The selection of the optimal conditions for thermolysis, such as the duration and temperature of the process, has been conducted. The thermolysis products are characterized for iodine adsorption activity, cumulative water pore volume, and for bulk density. The porous structure of the obtained products has been studied by scanning electron microscopy. Based on the results of the research conducted, it has been found that biochars obtained from husk and straw with a thermolysis duration of 30 minutes have low iodine sorption characteristics and water pore volumes. With an increase in the duration of thermolysis, the sorption characteristics improve, the optimal for the husk is the thermolysis duration of 60 minutes at a temperature of 500°C, and for straw, the optimal thermolysis duration is 60 minutes at a temperature of 300°C. The best option is biochar obtained from rice straw at a duration of 60 minutes and a thermolysis temperature of 300°C, having an iodine adsorption activity of 54.61%, a cumulative water pore volume of 0.941 cm3 /g and a bulk density of 169.29 g/dm3. The obtained biochars from rice husk and straw have been studied by scanning electron microscopy at 4300 and 5000 times magnification, and they have a developed porous structure.

Impacts of kerogen type and thermal maturity on methane and water adsorption isotherms: A molecular simulation approach

The molecular structure of kerogen is known to control the type, amount of petroleum generated as well as its interaction with reservoir fluids. The adsorption behavior of kerogen with respect to reservoir fluids can enhance our understanding of kerogen wetting properties. Therefore, quantifying the governing factors controlling the adsorption of water and methane in organic pores is critical in understanding fluid flow and adsorption phenomena in organic-rich mudrocks. In this paper, we perform molecular simulations (MS) and quantify water and methane adsorption isotherms on kerogen pore surfaces for the purpose of investigating the impact of kerogen molecular structure on kerogen-fluid interfacial interaction. To realistically represent kerogen structures, we use different kerogen molecular models to emulate kerogen of different types and thermal maturity. The kerogen molecules are condensed to form a porous kerogen structure. The Grand Canonical Monte Carlo simulation (GCMC) method is applied to calculate adsorption isotherms of methane and water molecules in kerogen nanopores. We compute the adsorption behavior of water and methane molecules on type I, II and III kerogen samples. The molecular simulations of increasing thermal maturity from IIA to IID at low pressures (less than 10 MPa) and temperature of 300 K in type II kerogen resulted in increasing methane adsorption capacity. At 5 MPa, the methane adsorption relatively increased 81% from IIA to IID. The adsorption capacity of methane is also shown to increase from type IA to IIA to IIIA. Similarly to methane, water adsorption capacity is found to increase from type IA to IIA to IIIA. However, water adsorption capacity on kerogen of different thermal maturity increases from IIB to IIA. Kerogen structures of types IID and IIC show very similar adsorption capacity nearly overlapping at four different pressures. However, water adsorption on IID and IIC kerogen is still found to be smaller compared to IIA and IIB. The outcomes of this work contribute to improving the understanding of the impact of kerogen molecular structure on adsorption of fluids on kerogen surfaces. Moreover, it can provide insights into fluid mobility assessments in organic-rich mudrocks by providing information about the adsorbed gas content on kerogen surfaces.

Study on evaporation rate of steel slag pervious concrete based on CT scanning

Pervious concrete can reduce the surface temperature and improve the outdoor environment through its own evaporation capacity. The unique pore structure makes pervious concrete different from ordinary concrete and has a great impact on its macro performance, such as mechanical, penetration, fatigue, durability, noise reduction performance. In this study, the correlation between water evaporation rate and pore structure parameters of steel slag pervious concrete (SPC) was analyzed, and an empirical model formula was proposed to characterize the water evaporation rate at different evaporation time. Evaporation experiments at different temperatures and different specimen heights were designed, and the evaporation of each specimen was obtained. The porosity and surface porosity of each specimen were determined by water replacement method and computed tomography (CT) scanning. The results show that the evaporation and initial evaporation rate of SPC increase with the increase of specimen height and temperature. The relationship between evaporation rate and evaporation time conforms to the exponential function distribution, showing a rapid decline stage and a gentle decline stage, with obvious inflection points. The pore size distribution and sphericity of SPC were analyzed, and its influence on evaporation rate was negligible. With the increase of height ratio, the tortuosity of SPC increases relatively, while the surface porosity decreases. The evaporation rate model of SPC considering the influence of specimen height, temperature, tortuosity and surface porosity is constructed. The research is helpful to improve the ecological design of SPC pavement and promote the application of SPC materials.

Spectral characterization of fouled railroad ballast using hyperspectral imaging

The presence of fouling contamination in railroad ballast is a growing concern that causes deterioration, poor drainage functionality, and early failure of railroad components. Evaluation and characterization of fouled ballast are crucial for determining and monitoring fouling content (FC) and moisture content (MC) in ballast. However, human inspection, destructive testing, field sampling, and most available nondestructive evaluation methods (NDE) for inspection purposes pose safety risks, undermine the stability of the railroad substructure, or provide limited information about the condition of the ballast. This study presents the results of the spectral characterization of laboratory ballast samples using hyperspectral imaging (HSI) sensor. Nineteen (19) clean, dry-fouled, and wet-fouled samples were prepared and evaluated using HSI. The reflectance of ballast samples with different levels of MC and FC was determined in Visible-Near infrared (VNIR) and Near-infrared (NIR) wavelength range from 400 nm to 1700 nm. Results showed that; the presence of trapped water in ballast pores and free water in ballast voids reduced the reflectance; an increase in the dry fouling content increased the reflectance, and MC in wet-fouled ballast showed a nonlinear relationship with the reflectance or absorbance property. The presence of water was prominent in wavelengths of 1350 nm to 1550 nm. A second-order polynomial fit was adopted for the absorbance and reflectance features plotted against the MC, and the coefficient of determination (R2) values were determined. The R2 for the absorbance and reflectance plots between 900 nm and 1700 nm were 0.7747 and 0.8336 in the sample with 5% FC and 0.8790 and 0.9278 with 15% FC, respectively. For the 1350 nm to 1500 nm wavelength range, the R2 increased by 27% and 13%, respectively, for 5% FC and then 5% and 0%, respectively, for 15% FC. This study shows that absorbance features are more prominent than the reflectance features for determining MC in fouled ballast, with high prospects of detecting, monitoring, and quantifying MC and FC contamination using the HSI method.

Characterizing unfrozen water content of saline silty clay during freezing and thawing based on superposition of freezing point reduction

Soil freezing point and unfrozen water content are essential parameters for the design of an artificial ground freezing (AGF) system. Previous studies on AGF technology mainly focused on soils in non-saline areas and unfrozen water content characteristic of soils in saline areas with different initial water contents was rarely investigated. Through a series of freezing point and nuclear magnetic resonance (NMR) tests, this paper investigated the influences of salt type (i.e. NaCl and Na2SO4), salt content, and initial water content on the freezing point of saline soils during freezing, unfrozen water content and pore size distribution during freezing and thawing. NaCl saline soils showed a salt content-dependent freezing point, deviating from Na2SO4 saline soils. Hysteresis effects were evident in the phase transition point, unfrozen water content, and pore size distribution during the full freeze-thaw cycle. NaCl saline soils exhibited a gradual reduction in dominant pore size with decreasing temperature during freezing and thawing, while Na2SO4 saline soils was associated with wider range of pore size. The Clapeyron equation was adopted and modified to accurately predict the freezing point and unfrozen water content of saline soils with different salt and initial water contents under different temperatures with help of newly introduced correction coefficients (i.e. a, b, k3, k4, and kt). Furthermore, the accuracy of the existing model in predicting cumulative pore size distribution was improved with help of a newly correction coefficient (i.e. β) through an regression analysis.

Evolution Characteristics of Coal Microstructure before and after Supercritical CO2 Treatment Based on the L-Weighing-LNMR Method

To accurately and quantitatively characterize the evolution of coal microstructures before and after supercritical CO2 treatment, this paper proposes a microstructural analysis for coal-rock based on low-field nuclear magnetic resonance (LNMR) technology, the L-weighing method. The experimental results of the L-weighing method and the LNMR method were compared and analyzed. The results showed that there were differences between the experimental results of the L-weighing method and the LNMR method, but the overall laws were basically the same. The L-weighing method quantitatively characterizes the water content in coal and determines water consumption and microscopic component extraction in coal with supercritical CO2, while the LNMR method only determines the dissolution of H-containing substances in the coal by supercritical CO2. According to the combined analysis with the L-weighing method and the LNMR method, after the supercritical CO2 entered the coal, it consumed 0.33 g of water from the coal and extracted 0.32 g of microscopic components from the coal, reacted chemically with both water and microscopic components in the coal, and provided effective water consumption and extraction of the coal. The supercritical CO2 increased the saturable water in the coal by 0.71 g, the porosity by 1.57%, and the pore seepage volume by a factor of 1.10, which expanded the volume and increased the permeability of the coal. After the reaction with supercritical CO2, the centrifugal water loss of the coal increased by 0.16 g, the T2 cutoff (T2C) of the coal had shifted to the left by 0.31 ms, and the free water volume of the coal had increased by a factor of 1.15, which enhanced the pore connectivity in the coal. The water consumption, extraction, volume expansion, permeability increase, and pore connectivity increase were primarily responsible for the changes in the coal microstructure effected by supercritical CO2.

Physical origins of freezing and melting temperature depressions of water in millimeter-sized pores

As a long-standing problem, the physics of freezing and melting temperature depressions of water in millimeter-sized pores remains elusive. We devised a series of experiments on the freezing and melting of water in glass tubes with varying tube diameters, water volumes, water-solid interfacial areas, and cooling rates. The results of the experiments indicate that the freezing temperature depression is highly correlated with the water-solid interfacial areas. It can be inferred that heterogeneous nucleation is the dominant physical origin for such freezing temperature depression. In contrast, melting temperature depression is orders of magnitude lower than that of freezing, and is independent of heating rate, water volume, water-solid interfacial area, and correlated with pore diameter, suggesting the governing role of capillarity. The recognized distinct physical origins of freezing and melting temperatures lead to the disparity between them, i.e., freezing and melting hysteresis. The findings resolve the controversy on the freezing mechanism of water in millimeter-sized pores, and can be used to better manipulate freezing and melting behaviors of pore water in various engineering applications, e.g., promoting or inhibiting freezing in biomaterials, and developing anti-freezing materials.