In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)wit...In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.展开更多
Biochar has been used as an environment-friendly enhancer to improve the hydraulic properties(e.g.suction and water retention)of soil.However,variations in densities alter the properties of the soil ebiochar mix.Such ...Biochar has been used as an environment-friendly enhancer to improve the hydraulic properties(e.g.suction and water retention)of soil.However,variations in densities alter the properties of the soil ebiochar mix.Such density variations are observed in agriculture(loosely compacted)and engineering(densely compacted)applications.The influence of biochar amendment on gas permeability of soil has been barely investigated,especially for soil with different densities.The major objective of this study is to investigate the water retention capacity,and gas permeability of biochar-amended soil(BAS)with different biochar contents under varying degree of compaction(DOC)conditions.In-house produced novel biochar was mixed with the soil at different amendment rates(i.e.biochar contents of 0%,5%and 10%).All BAS samples were compacted at three DOCs(65%,80%and 95%)in polyvinyl chloride(PVC)tubes.Each soil column was subjected to dryingewetting cycles,during which soil suction,water content,and gas permeability were measured.A simplified theoretical framework for estimating the void ratio of BAS was proposed.The experimental results reveal that the addition of biochar significantly decreased gas permeability kg as compared with that of bare soil(BS).However,the addition of 5%biochar is found to be optimum in decreasing kg with an increase of DOC(i.e.k_(g,65%)>k_(g,80%)>k_(g,95%))at a relatively low suction range(<200 kPa)because both biochar and compaction treatment reduce the connected pores.展开更多
In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acyla...In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.展开更多
Compressive stress and tensile stress were applied to concrete specimens using test rigs designed by RILEM TC 246-TDC. Ultrasonic wave velocity and autoclam permeability system were used to characterize the damage var...Compressive stress and tensile stress were applied to concrete specimens using test rigs designed by RILEM TC 246-TDC. Ultrasonic wave velocity and autoclam permeability system were used to characterize the damage variable and gas permeability coefficient of concrete, respectively. The experimental results show that the strain value of concrete increases with the increasing of stress level and loading time. The damage variable and gas permeability coefficient of concrete under compressive stress decrease at first and increase after a threshold value between 0 and 0.6. When the concrete is under tensile load, the damage variable and gas permeability coefficient increase with tensile stress, with a significant increase from 0.3 to 0.6 tensile stress. There is a strong linear relationship between the damage variable and the gas permeability coefficient, suggesting both as good indicators to characterize the damage of concrete under stress.展开更多
The effects of chemical structure, i. e. side chain structure and their contents, on thepermeability of pure SO_2, N_2 and their mixture gases for the sulfoxide grafted poly (vinylalcohol) (RVSO-PVA) membranes have be...The effects of chemical structure, i. e. side chain structure and their contents, on thepermeability of pure SO_2, N_2 and their mixture gases for the sulfoxide grafted poly (vinylalcohol) (RVSO-PVA) membranes have been investigated:where R=Me, Et, Pr, t-Bu and Ph. It was notable that introduction of sulfoxide group intoPVA side chain greatly enhanced the permselectivity of sulfur dioxide. SO_2 permeability andseparation factor of these polymers increased markedly as the size of side chain increased. Thesulfoxide content of the polymer also played an important role in the pure and mixture gasespermeation. Some explanations have been made to interpret this unique gas separation behaviour.展开更多
Two different freeze-thaw cycles(FTC)are considered in this study to assess the related impact on gas permeability and micro-pore structure of a mortar.These are the water-freezing/water-thawing(WF-WT)and the air-free...Two different freeze-thaw cycles(FTC)are considered in this study to assess the related impact on gas permeability and micro-pore structure of a mortar.These are the water-freezing/water-thawing(WF-WT)and the air-freezing/air-thawing(AF-AT)cycles.The problem is addressed experimentally through an advanced nuclear magnetic resonance(NMR)technique able to provide meaningful information on the relationships among gas permeability,pore structure,mechanical properties,and the number of cycles.It is shown that the mortar gas permeability increases with the number of FTCs,the increase factor being 20 and 12.83 after 40 cycles for the WF-WT and AF-AT,respectively.The results also confirm that gas permeability hysteresis phenomena occur during the confining pressure loading and unloading process.展开更多
Glass powder of various particle sizes(2,5,10 and 15μm)has been assessed as a possible cement substitute for mortars.Different replacement rates of cement(5%,10%,15%,and 20%)have been considered for all particle size...Glass powder of various particle sizes(2,5,10 and 15μm)has been assessed as a possible cement substitute for mortars.Different replacement rates of cement(5%,10%,15%,and 20%)have been considered for all particle sizes.The accessible porosity,compressive strength,gas permeability and microstructure have been investigated accordingly.The results have shown that adding glass powder up to 20%has a significantly negative effect on the porosity and compressive strength of mortar.The compressive strength initially rises with a 5%replacement and then decreases.Similarly,the gas permeability of the mortar displays a non-monotonic behavior;first,it decreases and then it grows with an increase in the glass powder content and particle size.The porosity and gas permeability attain a minimum for a 5%content and 10μm particle size.Application of a Nuclear magnetic resonance(NMR)technique has revealed that incorporating waste glass powder with a certainfineness can reduce the pore size and the number of pores of the mortar.Compared with the control mortar,the pore volume of the waste glass mortar with 5%and 10μm particle size is significantly reduced.When cement is partially replaced by glass powder with a particle size of 10μm and a 5%percentage,the penetration resistance and compressive strength of the mortar are significantly improved.展开更多
A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume...A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume properties in IPN were investigated. We found that in PU/ER IPN, the free volume hole size and fractional free volume showed a negative deviation due to closer segmental chain packing through some chemical bonding between PU and epoxy resin. Direct relationship between the gas permeability and the free volume has been established based on the free volume theory. Experimental results revealed that the free volume plays an important role in determining the gas diffusion and permeability.展开更多
Poly(4-methyl-1-pentene)hollow fiber membranes(PMP HFMs)are commonly used in gas separation membrane and artificial lung membrane in extracorporeal membrane oxygenation(ECMO),and its porous structure and mechanical pr...Poly(4-methyl-1-pentene)hollow fiber membranes(PMP HFMs)are commonly used in gas separation membrane and artificial lung membrane in extracorporeal membrane oxygenation(ECMO),and its porous structure and mechanical properties have a significant impact on the performance of the membrane material.In our work,PMP HFMs were prepared by thermally induced phase separation method.Subsequently,through characterization analysis of powder X-ray diffraction,universal tensile machine,scanning electron microscope and other instruments,the effects of PMP concentration,diluent ratio,quenching temperature,air gap distance and winding speed on the membrane performance were systematically investigated to obtain optimal preparation conditions for PMP HFMs.The results showed that the PMP HFMs prepared under optimal conditions possessed good gas permeability with a nitrogen flux of 10.5 ml·MPa^(-1)·cm^(-2)·min^(-1),a surface dense layer,and a good tensile strength of 9.33 MPa.We believed that this work could provide useful references for the application of PMP membranes in the medical field.展开更多
The permeability of copoly (1-trimethylsilyl-1-propyne-pentamethyldisilyl-1-propyne) membrane for twelve gases (0_2, N_2, CO_2, H_2, D_2, He, At, CH_4, C_2H_4, C_2H_6, C_3H_6 and C_3H_8) was examined. The basic laws o...The permeability of copoly (1-trimethylsilyl-1-propyne-pentamethyldisilyl-1-propyne) membrane for twelve gases (0_2, N_2, CO_2, H_2, D_2, He, At, CH_4, C_2H_4, C_2H_6, C_3H_6 and C_3H_8) was examined. The basic laws of solution and diffusion of the gases in the membrane were expounded preliminarily. It was found that a linear relationship between logarithm of diffusion coefficient (D) and critical molar volume (V_c) of the gases. The permeation characteristics of the gases in the copoly (1-trimethylsilyl-1-propyne-pentamethyldisilyl-1-propyne) membrane was also discussed.展开更多
The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy st...The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy storage systems in abandoned mines.To investigate this,nitrogen permeability tests were conducted on the interface samples of rockeconcrete interface in both consolidated and unconsolidated states under cyclic loading.The variations in the flow rate throughout the permeability process under different cycle numbers and load range conditions were investigated.The microscopic analysis at the interfaces was imaged using computed tomography scanning.The results indicated that the gas permeability of the cemented interfaces with different roughness values varied with confining pressure ranging from 10^(-13) m^(2) to 10^(-12) m^(2),whereas that of the non-cemented interfaces ranged from 10^(-12) m^(2) to 10^(-11) m^(2).A larger load variation range encompassed the permeability variation characteristics within a smaller variation range.The evolution pattern of the permeability ratio with the number of cycles was influenced by the inlet pressure.The greater the inlet pressure,the larger the increment ratio of the permeability.The permeability change patterns of interfaces with different roughness values were similar.Microscopic analysis revealed that pores inside the concrete were connected to the interface gaps.Under the coupling of stress and gas pressure,the gas could penetrate the crack tips or pores,accelerating the development of microcracks during the cyclic opening and closing of the pores.This study provides valuable insights into the safe long-term operation of underground high-pressure air storage.展开更多
Plant-biochar interaction has been recognized to affect the hydraulic properties of landfill cover soils,while its influence on landfill gas emission is rarely studied.This study investigated the coupled effects of bi...Plant-biochar interaction has been recognized to affect the hydraulic properties of landfill cover soils,while its influence on landfill gas emission is rarely studied.This study investigated the coupled effects of biochar and vegetation on gas permeability and emission in unsaturated landfill cover through an integrated theoretical modelling and laboratory investigation.First,a gas permeability model was developed for vegetated coarse-grained soils with biochar addition.Then,a well-instrumented laboratory column test and two tests from the literature,considering bare,grass,biochar and grass+biochar conditions,were used for model validation.Finally,a numerical parametric study was conducted to investigate the influence of root growth and drought conditions on the gas emission rate.Results showed that the developed model can satisfactorily capture the gas permeability of unsaturated soils at various degrees of saturation.The lowest water retention capacity,the highest gas permeability and gas emission rate after 24 months of growth were observed in the grassed column.However,adding biochar in vegetated soils can maximize the water retention capacity and decrease the gas permeability,resulting in the lowest gas emission rate.The measured gas emission rates for the four cases meet the recommended value by the design guideline.The parametric study showed that the increased root depth from 0.2 m to 0.4 m improved the gas emission rate by 170%in the grass case but decreased by 97%in the grass+biochar case.Under the severe drought condition with soil suction around 500 kPa,the gas emission rate in the grassed case exceeded the design value by 18%,while those in the biochar cases were far below the allowable value.Therefore,peanut shell biochar should be considered to amend the grassed landfill cover using coarse-grained soils as it can significantly improve engineering performance in reducing gas emissions under extreme drought conditions.展开更多
Challenges in water drainage within natural gas hydrate reservoirs in the Shenhu area of the South China Sea,characterized by high clay content and strong hydrophilicity,significantly hinder natural gas recovery.Exami...Challenges in water drainage within natural gas hydrate reservoirs in the Shenhu area of the South China Sea,characterized by high clay content and strong hydrophilicity,significantly hinder natural gas recovery.Examining the effects of gas pressure and liquid/gas saturation on gas permeability reveals essential insights for increasing gas production potential.We report gas displacement experiments on clayey-silt sediment samples,alongside X-ray computed tomography imaging,that reveal critical findings:a notable increase in flow rate and permeability as displacement pressure nears compaction pressure,highlighting the role of pressure management in enhancing recovery;water displacement from varying pore sizes under different pressures,highlighting the influence of pore size on fluid dynamics,and structural changes,including microfracture formation and a significant fracture that enlarges total pore space by about 15%,which collectively suggest methods to improve gas flow and recovery.Moreover,our analysis identifies average throat length,fractal dimension,and succolarity as principal controls on gas permeability,indicating the substantial impact of microstructural properties on extraction efficiency.These outcomes offer valuable strategies for optimizing natural gas hydrate reservoir development in the South China Sea,emphasizing the need for meticulous pressure and saturation control and in applying a deep understanding of microstructural dynamics.展开更多
Rarefaction effect appears when gas flows in micro/nano channels,so it is difficult to accurately predict real gas flow rate by using the classical theory.It is necessary to establish a more accurate and universal per...Rarefaction effect appears when gas flows in micro/nano channels,so it is difficult to accurately predict real gas flow rate by using the classical theory.It is necessary to establish a more accurate and universal permeability correction model to describe the flow behavior of rarefied gas.In this work,the gas flow in a plate micro-scale channel was numerically simulated using R26 moment method,and the simulation results were compared with those of the direct simulation Monte Carlo method(DSMC method)and R13 moment method.Then,a gas permeability correction model for plate micro-scale channels and circular micro-scale channels was established based on the simulation results of the R26 moment method,and used to describe the flow behavior of rarefied gas in micro-scale channels.Finally,the gas permeability correction co-efficient for different Knudsen numbers was calculated and compared with the prediction results of the Tang model,the available experimental data and the solution of linearized Boltzmann equation.The following research results were obtained.First,when the R26 moment method is used to describe the rarefaction effect of gas,its result is accordant with the calculation result of the DSMC method,and its calculation accuracy is higher than that of R13 moment method.Second,the gas permeability correction coefficient which is calculated by using the higher-order Knudsen's gas permeability correction model for plate micro-scale channels is in accordance with the experimental data and the solution of linearized Boltzmann equation.Third,the gas permeability correction coefficient which is calculated by using the higher-order Knudsen's gas permeability correction model for circular micro-scale channels is accordant with the solution of linearized Boltzmann equation.In conclusion,this higher-order Knudsen's gas permeability correction model is advantageous with high prediction precision and universality,and it can be used to describe the rarefaction effect of gas in micro/nano-scale channels.展开更多
Here,the effects of compatibilization and clay nanoparticles on the gas permeability of nanocomposites of poly-lactic acid(PLA)/thermoplastic starch(TPS)/nanoclay were discussed.TPS and compatibilized PLA/TPS were tai...Here,the effects of compatibilization and clay nanoparticles on the gas permeability of nanocomposites of poly-lactic acid(PLA)/thermoplastic starch(TPS)/nanoclay were discussed.TPS and compatibilized PLA/TPS were tailored in the first step.The starch with D-sorbitol as a plasticizer was mingled through the internal mixer.Afterward,the maleination method was utilized on PLA to ameliorate the compatibilization of PLA and TPS.In this regard,maleic anhydrate(MA)has been grafted on PLA in the presence of L101 as a peroxide initiator via melt mixing to obtain PLA-g-MA.The optimum content of PLAg-MA was about 4 phr,confirmed by DMTA and SEM.Noteworthy,the presence of PLA-g-MA has moderately improved the oxygen barrier.Then,the nanocomposites of PLA and TPS containing 1%of Cloisite-30B as well as the optimum compatibilizer(4phr),were produced by melt mixing in the masterbatch module leading to the formation of an extraordinary well-dispersed structure according to XRD patterns.The mixing order controlled the localization of nanosheets.It was concluded that the inclusion of 1%nanoclay in the PLA phase reduces the oxygen permeability by 55%compared to the pristine blend due to the tortuosity effect of nanosheets that are appropriately dispersed in the matrix.展开更多
Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shal...Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry’s law is used to describe dissolution. The K coefficient in Henry’s law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. The surface diffu- sion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. When 1/ increases,k/ kincreases, but the relationship is not linear as the Klinkenberg effect suggests. The effect of adsorption on the gas flow is significant in nanopores (r≤2 nm). Adsorption increases apparent permeability in shales at low pressures and decreases it at high pressures.展开更多
Membrane-based separation processes are new technology combined membrane separation with conventional separation. Hydrophobic porous membranes are often used in these processes. The structure of hydrophobic porous mem...Membrane-based separation processes are new technology combined membrane separation with conventional separation. Hydrophobic porous membranes are often used in these processes. The structure of hydrophobic porous membrane has significant effect on mass transfer process. The permeabilities of five kinds of gas, He, N2, O2, CO2 and water vapor, across six polytetrafluoroethylene(PTFE) flat membranes were tested experimentally. Results indicated that the greater the membrane mean pore size and the wider the pore size distribution are, the higher the gas permeability. A gas permeation model, including the effects of membrane structure parameter and gas properties, was established. A comprehensive characteristic parameter (including porosity, thickness and tortuosity) was found more effective to express the influence of membrane structure in gas permeation process. The predicted permeation coefficients were in good agreement with experimental data.展开更多
The gas separation properties of free- standing film of polyaniline (PANI) for gas pairs of He/N2, H_2/N_2. CO_2/N_2 and CO_2/CH_4 at room temperature were measured as a function of the protonation state. Variation of...The gas separation properties of free- standing film of polyaniline (PANI) for gas pairs of He/N2, H_2/N_2. CO_2/N_2 and CO_2/CH_4 at room temperature were measured as a function of the protonation state. Variation of the gas permeabilities coefficient of PANI with an insulator to metal transition upon the protonation processes was observed, which might be due to a change in both gas solubility coefficient and diffusion coefficient with the protonation state.展开更多
Six aromatic polyesters were prepared for gas separation membranes, and their permeation properties for hydrogen, oxygen, nitrogen, carbon dioxide, and methane were measured at 30 degrees C and 1 atmosphere by low pre...Six aromatic polyesters were prepared for gas separation membranes, and their permeation properties for hydrogen, oxygen, nitrogen, carbon dioxide, and methane were measured at 30 degrees C and 1 atmosphere by low pressure manometric method. The correlation between the gas transport behavior and molecular structure of aromatic polyester membrane is discussed. These data are interpreted qualitatively in terms of the calculated packing density, gas-polymer interaction, concentration of aryl bromine on backbone, and effect of silane group on main chain of polymer.展开更多
River sand is an essential component used as a fine aggregate in mortar and concrete.Due to unrestrained exploitation,river sand resources are gradually being exhausted.This requires alternative solutions.This study d...River sand is an essential component used as a fine aggregate in mortar and concrete.Due to unrestrained exploitation,river sand resources are gradually being exhausted.This requires alternative solutions.This study deals with the properties of cement mortar containing different levels of manufactured sand(MS)based on quartzite,used to replace river sand.The river sand was replaced at 20%,40%,60%and 80%with MS(by weight or volume).The mechanical properties,transfer properties,and microstructure were examined and compared to a control group to study the impact of the replacement level.The results indicate that the compressive strength can be improved by increasing such a level.The strength was improved by 35.1%and 45.5%over that of the control mortar at replacement levels of 60%and 80%,respectively.Although there was a weak link between porosity and gas permeability in the mortars with manufactured sand,the gas permeability decreased with growing the replacement level.The microstructure of the MS mortar was denser,and the cement paste had fewer microcracks with increasing the replacement level.展开更多
基金Funded by the National Natural Science Foundation of China project(Nos.52108219 and U21A20150)the Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.04-062407)the Research on Quality Control Technology of High-performance Concrete Prepared by Manufactured Sand(No.2020Y21)。
文摘In view of the increased focus on“green”and sustainable development and compliance with the national strategy for“carbon peak and carbon neutrality,”this study investigated the effect of replacing cement(0-20%)with limestone powder(stone powder)as a mineral admixture on the micro,meso,and macro properties of mortar.First,the applicability of stone powder was examined based on the physical filling and heat of hydration of stone powder-cement.Second,micro-meso testing methods,such as X-ray diffraction,scanning electron microscopy,thermogravimetry-differential scanning calorimetry,and nuclear magnetic resonance,were utilized to reveal the influencing mechanisms of stone powder on the microstructure of the mortar.Furthermore,the effect of stone powder on the compressive strength and gas permeability of the mortar was analyzed.Additionally,the time-dependent variations in the gas permeability and its functional relationship with the mechanical properties were determined.Finally,the correlation between the compressive strength and gas permeability with respect to the pore size of stone powder-doped mortar was established via gray-correlation analysis.The results show that an appropriate amount of stone powder(5%)can effectively improve the particle gradation,decelerate the release of the heat of hydration,increase the amount of hydration products,and improve the pore structure,thereby increasing the compressive strength and reducing the gas permeability coefficient.The gas permeability of stone powder-doped mortar was found to exhibit good time-dependent characteristics as well as a quadratic linear correlation with the compressive strength.The gray-correlation analysis results indicate that air pores exhibit the highest influence on the compressive strength and that the gas permeability coefficient is most significantly affected by large pores.
基金The authors would like to acknowledge the National Natural Science Foundation of China(Grant No.41907252)Shantou University Scientific Research Fund(Grant No.NTF17007)
文摘Biochar has been used as an environment-friendly enhancer to improve the hydraulic properties(e.g.suction and water retention)of soil.However,variations in densities alter the properties of the soil ebiochar mix.Such density variations are observed in agriculture(loosely compacted)and engineering(densely compacted)applications.The influence of biochar amendment on gas permeability of soil has been barely investigated,especially for soil with different densities.The major objective of this study is to investigate the water retention capacity,and gas permeability of biochar-amended soil(BAS)with different biochar contents under varying degree of compaction(DOC)conditions.In-house produced novel biochar was mixed with the soil at different amendment rates(i.e.biochar contents of 0%,5%and 10%).All BAS samples were compacted at three DOCs(65%,80%and 95%)in polyvinyl chloride(PVC)tubes.Each soil column was subjected to dryingewetting cycles,during which soil suction,water content,and gas permeability were measured.A simplified theoretical framework for estimating the void ratio of BAS was proposed.The experimental results reveal that the addition of biochar significantly decreased gas permeability kg as compared with that of bare soil(BS).However,the addition of 5%biochar is found to be optimum in decreasing kg with an increase of DOC(i.e.k_(g,65%)>k_(g,80%)>k_(g,95%))at a relatively low suction range(<200 kPa)because both biochar and compaction treatment reduce the connected pores.
基金financially supported by the National Natural Science Foundation of China(Nos.21174151 and 51103167)Main Direction Program of Knowledge Innovation of Chinese Academy of Sciences(Nos.KJCX2-YW-H-19 and KJCX2-YW-H30-03)the Major State Basic Research Development Program of China(973 Program)(No.2010CB934705)
文摘In this work, four kinds of cellulose aliphatate esters, cellulose acetate （CA）, cellulose propionate （CP）, cellulose butyrate （CB） and cellulose acetate butyrate （CAB） are synthesized by the homogeneous acylation reactions in cellulose/AmimC1 solutions. These cellulose aliphatate esters are used to prepare gas separation membranes and the effects of molecular structure, such as substituent type, degree of substitution （DS） and distribution of substituents, on the gas permeability are studied. For CAs, as the DS increases, their gas permeabilities for all five gases （02, N2, CH4, CO and CO2） increase, and the ideal permselectivity significantly increases first and then slightly decreases. At similar DS value, the homogenously synthesized CA （distribution order of acetate substituent： C6 〉 C3 〉 C2） is superior to the heterogeneously synthesized CA （distribution order of acetate substituent： C3 〉 C2 〉 C6） in gas separation. With the increase of chain length of aliphatate substituents from acetate to propionate, and to butyrate, the gas permeability of cellulose aliphatate esters gradually increases. The cellulose mixed ester CAB with short acetate groups and relatively long butyrate groups exhibits higher gas permeability or better permselectivity than individual CA or CB via the alteration of the DS of two substituents.
基金Funded by the National Natural Science Foundation of China(No.51320105016)
文摘Compressive stress and tensile stress were applied to concrete specimens using test rigs designed by RILEM TC 246-TDC. Ultrasonic wave velocity and autoclam permeability system were used to characterize the damage variable and gas permeability coefficient of concrete, respectively. The experimental results show that the strain value of concrete increases with the increasing of stress level and loading time. The damage variable and gas permeability coefficient of concrete under compressive stress decrease at first and increase after a threshold value between 0 and 0.6. When the concrete is under tensile load, the damage variable and gas permeability coefficient increase with tensile stress, with a significant increase from 0.3 to 0.6 tensile stress. There is a strong linear relationship between the damage variable and the gas permeability coefficient, suggesting both as good indicators to characterize the damage of concrete under stress.
基金This project is supported by the National Education Commission of China and the Technology Commission of Zhejiang Province.
文摘The effects of chemical structure, i. e. side chain structure and their contents, on thepermeability of pure SO_2, N_2 and their mixture gases for the sulfoxide grafted poly (vinylalcohol) (RVSO-PVA) membranes have been investigated:where R=Me, Et, Pr, t-Bu and Ph. It was notable that introduction of sulfoxide group intoPVA side chain greatly enhanced the permselectivity of sulfur dioxide. SO_2 permeability andseparation factor of these polymers increased markedly as the size of side chain increased. Thesulfoxide content of the polymer also played an important role in the pure and mixture gasespermeation. Some explanations have been made to interpret this unique gas separation behaviour.
基金supported by the National Natural Science Foundation of China(Grant No.51709097).
文摘Two different freeze-thaw cycles(FTC)are considered in this study to assess the related impact on gas permeability and micro-pore structure of a mortar.These are the water-freezing/water-thawing(WF-WT)and the air-freezing/air-thawing(AF-AT)cycles.The problem is addressed experimentally through an advanced nuclear magnetic resonance(NMR)technique able to provide meaningful information on the relationships among gas permeability,pore structure,mechanical properties,and the number of cycles.It is shown that the mortar gas permeability increases with the number of FTCs,the increase factor being 20 and 12.83 after 40 cycles for the WF-WT and AF-AT,respectively.The results also confirm that gas permeability hysteresis phenomena occur during the confining pressure loading and unloading process.
基金This work is supported by the National Natural Science Foundation of China(No.51709097).
文摘Glass powder of various particle sizes(2,5,10 and 15μm)has been assessed as a possible cement substitute for mortars.Different replacement rates of cement(5%,10%,15%,and 20%)have been considered for all particle sizes.The accessible porosity,compressive strength,gas permeability and microstructure have been investigated accordingly.The results have shown that adding glass powder up to 20%has a significantly negative effect on the porosity and compressive strength of mortar.The compressive strength initially rises with a 5%replacement and then decreases.Similarly,the gas permeability of the mortar displays a non-monotonic behavior;first,it decreases and then it grows with an increase in the glass powder content and particle size.The porosity and gas permeability attain a minimum for a 5%content and 10μm particle size.Application of a Nuclear magnetic resonance(NMR)technique has revealed that incorporating waste glass powder with a certainfineness can reduce the pore size and the number of pores of the mortar.Compared with the control mortar,the pore volume of the waste glass mortar with 5%and 10μm particle size is significantly reduced.When cement is partially replaced by glass powder with a particle size of 10μm and a 5%percentage,the penetration resistance and compressive strength of the mortar are significantly improved.
基金Supported by the National Natural Science Foundation of China (20374038)
文摘A series of polyurethane/epoxy resin interpenetrating polymer networks （PU/ER IPN） were studied by positron annihilation lifetime spectroscopy （PALS）. The effects of epoxy resin type and content on the free volume properties in IPN were investigated. We found that in PU/ER IPN, the free volume hole size and fractional free volume showed a negative deviation due to closer segmental chain packing through some chemical bonding between PU and epoxy resin. Direct relationship between the gas permeability and the free volume has been established based on the free volume theory. Experimental results revealed that the free volume plays an important role in determining the gas diffusion and permeability.
基金support of thiswork by Science Fund of State Key Laboratory of Tribology,Tsinghua University(61012205321).
文摘Poly(4-methyl-1-pentene)hollow fiber membranes(PMP HFMs)are commonly used in gas separation membrane and artificial lung membrane in extracorporeal membrane oxygenation(ECMO),and its porous structure and mechanical properties have a significant impact on the performance of the membrane material.In our work,PMP HFMs were prepared by thermally induced phase separation method.Subsequently,through characterization analysis of powder X-ray diffraction,universal tensile machine,scanning electron microscope and other instruments,the effects of PMP concentration,diluent ratio,quenching temperature,air gap distance and winding speed on the membrane performance were systematically investigated to obtain optimal preparation conditions for PMP HFMs.The results showed that the PMP HFMs prepared under optimal conditions possessed good gas permeability with a nitrogen flux of 10.5 ml·MPa^(-1)·cm^(-2)·min^(-1),a surface dense layer,and a good tensile strength of 9.33 MPa.We believed that this work could provide useful references for the application of PMP membranes in the medical field.
文摘The permeability of copoly (1-trimethylsilyl-1-propyne-pentamethyldisilyl-1-propyne) membrane for twelve gases (0_2, N_2, CO_2, H_2, D_2, He, At, CH_4, C_2H_4, C_2H_6, C_3H_6 and C_3H_8) was examined. The basic laws of solution and diffusion of the gases in the membrane were expounded preliminarily. It was found that a linear relationship between logarithm of diffusion coefficient (D) and critical molar volume (V_c) of the gases. The permeation characteristics of the gases in the copoly (1-trimethylsilyl-1-propyne-pentamethyldisilyl-1-propyne) membrane was also discussed.
基金supported by the National Natural Science Foundation of China(Grant No.52409132)China Postdoctoral Science Foundation(Grant No.2024M751813)the Major key technical research projects of Shandong Energy Group(Grant No.SNKJ2023A07-R14).
文摘The structural integrity of the interface between a concrete plug and the surrounding rock may be compromised during frequent cycles of air charging,discharging,and storage,which is typical of compressed air energy storage systems in abandoned mines.To investigate this,nitrogen permeability tests were conducted on the interface samples of rockeconcrete interface in both consolidated and unconsolidated states under cyclic loading.The variations in the flow rate throughout the permeability process under different cycle numbers and load range conditions were investigated.The microscopic analysis at the interfaces was imaged using computed tomography scanning.The results indicated that the gas permeability of the cemented interfaces with different roughness values varied with confining pressure ranging from 10^(-13) m^(2) to 10^(-12) m^(2),whereas that of the non-cemented interfaces ranged from 10^(-12) m^(2) to 10^(-11) m^(2).A larger load variation range encompassed the permeability variation characteristics within a smaller variation range.The evolution pattern of the permeability ratio with the number of cycles was influenced by the inlet pressure.The greater the inlet pressure,the larger the increment ratio of the permeability.The permeability change patterns of interfaces with different roughness values were similar.Microscopic analysis revealed that pores inside the concrete were connected to the interface gaps.Under the coupling of stress and gas pressure,the gas could penetrate the crack tips or pores,accelerating the development of microcracks during the cyclic opening and closing of the pores.This study provides valuable insights into the safe long-term operation of underground high-pressure air storage.
基金Fundamental Research Funds for the Central Universities(Grant No.3221002220A1)State Key Laboratory of Subtropical Building Science in South China University of Technology(Grant No.2022ZC01).
文摘Plant-biochar interaction has been recognized to affect the hydraulic properties of landfill cover soils,while its influence on landfill gas emission is rarely studied.This study investigated the coupled effects of biochar and vegetation on gas permeability and emission in unsaturated landfill cover through an integrated theoretical modelling and laboratory investigation.First,a gas permeability model was developed for vegetated coarse-grained soils with biochar addition.Then,a well-instrumented laboratory column test and two tests from the literature,considering bare,grass,biochar and grass+biochar conditions,were used for model validation.Finally,a numerical parametric study was conducted to investigate the influence of root growth and drought conditions on the gas emission rate.Results showed that the developed model can satisfactorily capture the gas permeability of unsaturated soils at various degrees of saturation.The lowest water retention capacity,the highest gas permeability and gas emission rate after 24 months of growth were observed in the grassed column.However,adding biochar in vegetated soils can maximize the water retention capacity and decrease the gas permeability,resulting in the lowest gas emission rate.The measured gas emission rates for the four cases meet the recommended value by the design guideline.The parametric study showed that the increased root depth from 0.2 m to 0.4 m improved the gas emission rate by 170%in the grass case but decreased by 97%in the grass+biochar case.Under the severe drought condition with soil suction around 500 kPa,the gas emission rate in the grassed case exceeded the design value by 18%,while those in the biochar cases were far below the allowable value.Therefore,peanut shell biochar should be considered to amend the grassed landfill cover using coarse-grained soils as it can significantly improve engineering performance in reducing gas emissions under extreme drought conditions.
基金grateful to the National Natural Science Foundation of China(Nos.42302143,42172159,U2244223)China Postdoctoral Science Foundation(No.2023M743870)+2 种基金China Geological Survey Project(No.DD20211350)the Science Foundation of China University of Petroleum,Beijing(No.2462023XKBH002)DE gratefully acknowledges support from the G.Albert Shoemaker endowment.
文摘Challenges in water drainage within natural gas hydrate reservoirs in the Shenhu area of the South China Sea,characterized by high clay content and strong hydrophilicity,significantly hinder natural gas recovery.Examining the effects of gas pressure and liquid/gas saturation on gas permeability reveals essential insights for increasing gas production potential.We report gas displacement experiments on clayey-silt sediment samples,alongside X-ray computed tomography imaging,that reveal critical findings:a notable increase in flow rate and permeability as displacement pressure nears compaction pressure,highlighting the role of pressure management in enhancing recovery;water displacement from varying pore sizes under different pressures,highlighting the influence of pore size on fluid dynamics,and structural changes,including microfracture formation and a significant fracture that enlarges total pore space by about 15%,which collectively suggest methods to improve gas flow and recovery.Moreover,our analysis identifies average throat length,fractal dimension,and succolarity as principal controls on gas permeability,indicating the substantial impact of microstructural properties on extraction efficiency.These outcomes offer valuable strategies for optimizing natural gas hydrate reservoir development in the South China Sea,emphasizing the need for meticulous pressure and saturation control and in applying a deep understanding of microstructural dynamics.
文摘Rarefaction effect appears when gas flows in micro/nano channels,so it is difficult to accurately predict real gas flow rate by using the classical theory.It is necessary to establish a more accurate and universal permeability correction model to describe the flow behavior of rarefied gas.In this work,the gas flow in a plate micro-scale channel was numerically simulated using R26 moment method,and the simulation results were compared with those of the direct simulation Monte Carlo method(DSMC method)and R13 moment method.Then,a gas permeability correction model for plate micro-scale channels and circular micro-scale channels was established based on the simulation results of the R26 moment method,and used to describe the flow behavior of rarefied gas in micro-scale channels.Finally,the gas permeability correction co-efficient for different Knudsen numbers was calculated and compared with the prediction results of the Tang model,the available experimental data and the solution of linearized Boltzmann equation.The following research results were obtained.First,when the R26 moment method is used to describe the rarefaction effect of gas,its result is accordant with the calculation result of the DSMC method,and its calculation accuracy is higher than that of R13 moment method.Second,the gas permeability correction coefficient which is calculated by using the higher-order Knudsen's gas permeability correction model for plate micro-scale channels is in accordance with the experimental data and the solution of linearized Boltzmann equation.Third,the gas permeability correction coefficient which is calculated by using the higher-order Knudsen's gas permeability correction model for circular micro-scale channels is accordant with the solution of linearized Boltzmann equation.In conclusion,this higher-order Knudsen's gas permeability correction model is advantageous with high prediction precision and universality,and it can be used to describe the rarefaction effect of gas in micro/nano-scale channels.
基金supported by the National Natural Science Foundation of China[Grant No.51703083]the Project“Fibre materials and products for emergency support and public safety”from Jiangsu New Horizon Advanced Functional Fibre Innovation Center Co.Ltd.[Grant No.2020-fx020026]。
文摘Here,the effects of compatibilization and clay nanoparticles on the gas permeability of nanocomposites of poly-lactic acid(PLA)/thermoplastic starch(TPS)/nanoclay were discussed.TPS and compatibilized PLA/TPS were tailored in the first step.The starch with D-sorbitol as a plasticizer was mingled through the internal mixer.Afterward,the maleination method was utilized on PLA to ameliorate the compatibilization of PLA and TPS.In this regard,maleic anhydrate(MA)has been grafted on PLA in the presence of L101 as a peroxide initiator via melt mixing to obtain PLA-g-MA.The optimum content of PLAg-MA was about 4 phr,confirmed by DMTA and SEM.Noteworthy,the presence of PLA-g-MA has moderately improved the oxygen barrier.Then,the nanocomposites of PLA and TPS containing 1%of Cloisite-30B as well as the optimum compatibilizer(4phr),were produced by melt mixing in the masterbatch module leading to the formation of an extraordinary well-dispersed structure according to XRD patterns.The mixing order controlled the localization of nanosheets.It was concluded that the inclusion of 1%nanoclay in the PLA phase reduces the oxygen permeability by 55%compared to the pristine blend due to the tortuosity effect of nanosheets that are appropriately dispersed in the matrix.
基金supported by the Department of Energy under Award Number DE-FE0024311
文摘Gas sorption and non-Darcy flow are two important issues for shale gas reservoirs. The sorption consists of dissolution and adsorption. Dissolved gas and adsorbed gas are different. The former is dissolved in the shale matrix, while the latter is concentrated near the solid walls of pores. In this paper, the Langmuir equation is used to describe adsorption and Henry’s law is used to describe dissolution. The K coefficient in Henry’s law of 0.052 mmol/(MPa g TOC) is obtained by matching experimental data. The amount of dissolved gas increases linearly when pressure increases. Using only the Langmuir equation without considering dissolution can lead to a significant underestimation of the amount of sorbed gas in shales. For non-Darcy gas flow, the apparent permeability model for free gas is established by combining slip flow and Knudsen flow. For adsorbed gas, the surface diffusion effect is also considered in this model. The surface diffu- sion coefficient is suggested to be of the same scale as the gas self-diffusion coefficient, and the corresponding effective permeability is derived. When 1/ increases,k/ kincreases, but the relationship is not linear as the Klinkenberg effect suggests. The effect of adsorption on the gas flow is significant in nanopores (r≤2 nm). Adsorption increases apparent permeability in shales at low pressures and decreases it at high pressures.
基金Supported by the 863 Hi-Tech. Research and Development Program of China (No. 2002AA649280, No. 2002AA304030),National Natural Science Foundation of China (No. 20206002), Beijing NOVA program (H013610250112), University Doctor Science Foundation of China
文摘Membrane-based separation processes are new technology combined membrane separation with conventional separation. Hydrophobic porous membranes are often used in these processes. The structure of hydrophobic porous membrane has significant effect on mass transfer process. The permeabilities of five kinds of gas, He, N2, O2, CO2 and water vapor, across six polytetrafluoroethylene(PTFE) flat membranes were tested experimentally. Results indicated that the greater the membrane mean pore size and the wider the pore size distribution are, the higher the gas permeability. A gas permeation model, including the effects of membrane structure parameter and gas properties, was established. A comprehensive characteristic parameter (including porosity, thickness and tortuosity) was found more effective to express the influence of membrane structure in gas permeation process. The predicted permeation coefficients were in good agreement with experimental data.
文摘The gas separation properties of free- standing film of polyaniline (PANI) for gas pairs of He/N2, H_2/N_2. CO_2/N_2 and CO_2/CH_4 at room temperature were measured as a function of the protonation state. Variation of the gas permeabilities coefficient of PANI with an insulator to metal transition upon the protonation processes was observed, which might be due to a change in both gas solubility coefficient and diffusion coefficient with the protonation state.
文摘Six aromatic polyesters were prepared for gas separation membranes, and their permeation properties for hydrogen, oxygen, nitrogen, carbon dioxide, and methane were measured at 30 degrees C and 1 atmosphere by low pressure manometric method. The correlation between the gas transport behavior and molecular structure of aromatic polyester membrane is discussed. These data are interpreted qualitatively in terms of the calculated packing density, gas-polymer interaction, concentration of aryl bromine on backbone, and effect of silane group on main chain of polymer.
基金supported by the National Natural Science Foundation of China(No.51709097).
文摘River sand is an essential component used as a fine aggregate in mortar and concrete.Due to unrestrained exploitation,river sand resources are gradually being exhausted.This requires alternative solutions.This study deals with the properties of cement mortar containing different levels of manufactured sand(MS)based on quartzite,used to replace river sand.The river sand was replaced at 20%,40%,60%and 80%with MS(by weight or volume).The mechanical properties,transfer properties,and microstructure were examined and compared to a control group to study the impact of the replacement level.The results indicate that the compressive strength can be improved by increasing such a level.The strength was improved by 35.1%and 45.5%over that of the control mortar at replacement levels of 60%and 80%,respectively.Although there was a weak link between porosity and gas permeability in the mortars with manufactured sand,the gas permeability decreased with growing the replacement level.The microstructure of the MS mortar was denser,and the cement paste had fewer microcracks with increasing the replacement level.
