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Moisture diffusion behavior of permeable fiber-reinforced polymer composite

Jianjiang YANG, Qingsheng YANG, Lianhua MA, Wei LIU,

《机械工程前沿（英文）》 2010年第5卷第3期页码 347-352 doi: 10.1007/s11465-010-0093-y

摘要： A unit cell approach is employed to predict the effective moisture diffusion property in fiber-reinforced biopolymer. The permeable fibers distributed in the matrix are taken as inclusion phases in the system. Based on a unit cell model, the calculation method for moisture diffusion coefficients is developed in this paper. Moisture diffusion property and effective diffusion coefficients are numerically investigated under different temperature and volume fractions of fibers. The calculated results agree well with Gueribiz’s solutions. Therefore, it is reliable in predicting moisture diffusion property of composite using the unit cell model. The present result shows that the effective diffusion coefficient of a composite depends on both temperature and volume fraction of fibers. The effective diffusion coefficient of regular hexagon pattern composite is larger than that of square pattern at the same temperature and volume fraction.

关键词： fiber-reinforced biopolymer effective diffusion coefficient unit cell finite element modeling (FEM)

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Influence of initial curing conditions and exposure environments on chloride migration in concrete using electrochemical method

Wen XUE, Weiliang JIN, Hiroshi YOKOTA,

《结构与土木工程前沿（英文）》 2010年第4卷第3期页码 348-353 doi: 10.1007/s11709-010-0077-3

摘要： To investigate the influence of initial curing conditions and exposure environments on chloride ions’ migration in concrete, the specimens that were cured in different conditions and placed in several marine environments were studied. The amount of chloride ions passing through the specimen’s section was monitored in the accelerated chloride migration test. The effective chloride diffusion coefficients () were calculated from the steady-state on the basis of Nernst-Planck’s equation. The results indicated that the initial curing conditions and the wet-dry interval of external environments have coupling influence on effective diffusion coefficient of chloride ion significantly. reflected the density and pore connectivity of concrete. The co-effects of the initial curing condition and following exposure environment should be taken into account in durability design for concrete structure located in marine environment.

关键词： durability effective diffusion coefficient steady-state migration test

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Diagnosis method based on wavelet coefficient scale relativity correlation dimension for fault

GU Junjie, TIAN Jin, PENG Xuezhi

《能源前沿（英文）》 2008年第2卷第2期页码 164-168 doi: 10.1007/s11708-008-0031-4

摘要： Correlation dimension as a tool to describe machinery condition is introduced. Vibration signals of the fan under different working conditions are analyzed using a threshold filtering algorithm based on the region relativity of the wavelet coefficients for reducing noise. The result shows that the characteristics of the signal could be preserved completely. The correlation dimension is able to identify conditions of the fan with faults compared with the normal condition, thereby providing an effective technology for condition monitoring and fault diagnosis of mechanical equipment.

关键词： effective technology monitoring mechanical equipment relativity Correlation

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Correlation of chloride diffusion coefficient and microstructure parameters in concrete: A comparative

Yurong ZHANG, Shengxuan XU, Yanhong GAO, Jie GUO, Yinghui CAO, Junzhi ZHANG

《结构与土木工程前沿（英文）》 2020年第14卷第6期页码 1509-1519 doi: 10.1007/s11709-020-0681-9

摘要： Permeability is a major indicator of concrete durability, and depends primarily on the microstructure characteristics of concrete, including its porosity and pore size distribution. In this study, a variety of concrete samples were prepared to investigate their microstructure characteristics via nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and X-ray computed tomography (X-CT). Furthermore, the chloride diffusion coefficient of concrete was measured to explore its correlation with the microstructure of the concrete samples. Results show that the proportion of pores with diameters<1000 nm obtained by NMR exceeds that obtained by MIP, although the difference in the total porosity determined by both methods is minimal. X-CT measurements obtained a relatively small porosity; however, this likely reflects the distribution of large pores more accurately. A strong correlation is observed between the chloride diffusion coefficient and the porosity or contributive porosity of pores with sizes<1000 nm. Moreover, microstructure parameters measured via NMR reveal a lower correlation coefficient versus the chloride diffusion coefficient relative to the parameters determined via MIP, as NMR can measure non-connected as well as connected pores. In addition, when analyzing pores with sizes>50 µm, X-CT obtains the maximal contributive porosity, followed by MIP and NMR.

关键词： permeability microstructure NMR MIP X-CT

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Coulomb-type solutions for passive earth pressure with steady seepage

WANG Junjie, CHAI Hejun, LIN Xin, XU Jiamei

《结构与土木工程前沿（英文）》 2008年第2卷第1期页码 56-66 doi: 10.1007/s11709-008-0001-2

摘要： Present paper deals with the computing of passive earth pressure acting on the vertical rigid retaining wall supporting the soil mass subjected to water seepage. The basic assumptions of Coulomb’s theory and the 2-dimensional steady flow function are used. Three Coulomb-type solutions for the passive earth pressures are presented for the walls provided with three different drainage systems respectively. Based on the general solutions, the variations of the critical inclination of the failure surface and the coefficient of passive earth pressure with increasing the effective friction angle of the soil mass, the soil/structure friction angle, and the water/soil unit weight ratio are discussed. Two tables with values of the coefficients of passive earth pressure for Cases 1 and 3 respectively are also presented.

关键词： function coefficient Coulomb-type effective friction different drainage

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基于修正氯离子扩散理论模型和海洋大数据的中国北方海洋混凝土结构工程服役寿命设计 Article

冯滔滔, 余红发, 谭永山, 麻海燕, 许梅, 岳承军

《工程（英文）》 2022年第17卷第10期页码 123-139 doi: 10.1016/j.eng.2021.03.030

摘要：

本研究通过试验研究和海洋工程耐久性参数大数据集的调研，明确了中国北方海洋工程耐久性设计参数的取值、范围和分布类型。基于修正的氯离子扩散理论模型和可靠性理论，计算了浪溅区、潮汐区和水下区混凝土结构的服役寿命。设计了满足100 年或120 年服役寿命要求的混凝土配合比，并提出了保护层厚度要求。此外，对比了边界条件（C_s）和扩散系数（D_f）的不同时变关系对服役寿命的影响，结果表明，本研究采用的时变关系（即C_s持续增加后保持稳定，D_f持续降低后保持稳定）对于海洋环境下混凝土结构的耐久性设计具有有利效应。

关键词：大数据集修正的理论模型可靠性理论服役寿命边界条件扩散系数

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A comprehensive assessment on the durability of gas diffusion electrode materials in PEM fuel cell stack

Arunkumar JAYAKUMAR

《能源前沿（英文）》 2019年第13卷第2期页码 325-338 doi: 10.1007/s11708-019-0618-y

摘要： Polymer electrolyte membrane (PEM) fuel cell is the most promising among the various types of fuel cells. Though it has found its applications in numerous fields, the cost and durability are key barriers impeding the commercialization of PEM fuel cell stack. The crucial and expensive component involved in it is the gas diffusion electrode (GDE) and its degradation, which limits the performance and life of the fuel cell stack. A critical analysis and comprehensive understanding of the structural and functional properties of various materials involved in the GDE can help us to address the related durability and cost issues. This paper reviews the key GDE components, and in specific, the root causes influencing the durability. It also envisages the role of novel materials and provides a critical recommendation to improve the GDE durability.

关键词： PEM fuel cell gas diffusion electrode(GDE) gas diffusion layer(GDL) membrane electrode assembly durability fuel cell catalyst

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Coupled diffusion of chloride and other ions in saturated concrete

Nattapong DAMRONGWIRIYANUPAP, Linyuan LI, Yunping XI

《结构与土木工程前沿（英文）》 2011年第5卷第3期页码 267-277 doi: 10.1007/s11709-011-0112-z

摘要： Corrosion of reinforcing steel due to chloride ions is one of the severe deterioration problems in long-term performance of reinforced concrete structures. The deterioration process is frequently found in marine concrete structures, highway pavements, and bridges exposed to deicing salts. The diffusion of chloride ions is associated and strongly affected by other ions in the pore solution in concrete. In this paper, chloride penetration into concrete structures was mathematically characterized by the Nernst-Planck equation which considered not only diffusion mechanism of the chloride ions but also ionic interaction among other ions coming from externally applied deicers and within the Portland cement paste. Electroneutrality was used to determine the electrostatic potential induced by the ionic interaction. The material models of chloride binding capacity and chloride diffusion coefficient were incorporated in the governing equations. The governing equations were solved by using finite element method. A numerical example was used to illustrate the coupling effect of multi-ionic interactions and the effect of influential parameters. The numerical results obtained from the present model agreed very well with available test data.

关键词： diffusion chloride concrete Nernst-Planck equation durability

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特低渗透油田提压注水效果探讨与实践

张洪亮

《中国工程科学》 2012年第14卷第4期页码 62-64

摘要：

大庆西部外围地区特低渗透扶余油层具有埋藏深、厚度薄、砂体零散的特点，针对首次注水开发的特低渗透油田注水井吸水能力差、难以有效开发动用的实际，在搞清该区块微观特征的基础上，为确保特低渗透储层达到建立有效驱替，“注够水、注好水”的目的，经过反复理论研究和论证，提出了单井增压注水试验，现场应用后注水井能够完成配注，周围油井明显见到增油效果，实现了特低渗透储层有效驱替。利用无源微地震和同位素监测资料分析，改善了吸水状况，缓解了层间矛盾，储层动用程度得到提高。随注水压力升高降低，注水波及区范围随之升高、降低，增压注

关键词：增压注水无源微地震特低渗透油田波及系数有效驱替

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Experimental study of humid air reverse diffusion combustion in a turbulent flow field

GE Bing, ZANG Shusheng, GU Xin

《能源前沿（英文）》 2007年第1卷第4期页码 428-434 doi: 10.1007/s11708-007-0062-6

摘要： Experiments were performed to investigate the differences between the propane/air turbulent diffusion reactive flows past bluff-body and the propane/humid air turbulent diffusion reactive flows in the same conditions. The velocity

关键词： propane/humid propane/air turbulent bluff-body turbulent diffusion

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Preparation of a Pb loaded gas diffusion electrode and its application to CO

Ang LI, Hua WANG, Jinyu HAN, Li LIU

《化学科学与工程前沿（英文）》 2012年第6卷第4期页码 381-388 doi: 10.1007/s11705-012-1216-2

摘要： A Pb loaded gas diffusion electrode was fabricated and used for the electroreduction of CO to formic acid. The Pb/C catalyst was prepared by isometric impregnation. The crystal structure and morphology of the Pb/C catalyst were characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The preparation conditions of the gas diffusion electrode were optimized by adjusting the amounts of polytetrafluoroethylene (PTFE) in the gas diffusion layer and acetylene black in the catalytic layer. The electrochemical performance of the as-prepared gas diffusion electrode was studied by chronoamperometry and cyclic voltammetry. The optimized gas diffusion electrode showed good catalytic performance for the electroreduction of CO . The current efficiency of formic acid after 1 h of operation reached a maximum of 22% at -2.0 V versus saturated calomel electrode (SCE).

关键词： electroreduction carbon dioxide lead catalyst gas diffusion electrode formic acid

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evaluation of renal function using diffusion weighted imaging and diffusion tensor imaging in type 2

null

《医学前沿（英文）》 2014年第8卷第4期页码 471-476 doi: 10.1007/s11684-014-0365-8

摘要：

This work aims to estimate the value of diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) in detecting early-stage kidney injury in type 2 diabetic patients with normoalbuminuria (NAU) versus microalbuminuria (MAU) prospectively. A total of 30 T2DM patients with normal kidney function were recruited and assigned to the NAU group (n = 14) or MAU group (n= 16) according to 8 h overnight urinary albuminuria excretion rate (AER) results. A contemporary cohort of health check-up recipients were included as controls (n = 12). DWI and DTI scans were performed on bilateral kidney using SE single-shot EPI, and apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the renal parenchyma was determined from ADC and FA maps of the three groups. ADC and FA values were compared among the three groups. According to DWI with a b value of 400 s/mm², the MAU and NAU groups showed significantly lowered mean ADC values compared with the healthy controls (P<0.01). The mean ADC in the MAU group [(2.22±0.07)×10^–3 mm²/s] was slightly lower than that of the NAU group [(2.31±0.22)×10^–3 mm²/s], but this difference was not statistically significant (P>0.05). The FA value in the MAU group was higher than that in the control group (0.45±0.07 vs. 0.39±0.03, P = 0.004) but did not differ from that in the NAU group (0.42±0.03) (P>0.05). ADC and FA values may be more sensitive than urine AER in reflecting early-stage kidney injury and, hence, may facilitate earlier detection and quantitative evaluation of kidney injury in T2DM patients. Combined evaluation of ADC and FA values may provide a better quantitative approach for identifying diabetic nephropathy at early disease stages.

关键词： type 2 diabetes mellitus microalbuminuria diffusion weighted imaging diffusion tensor imaging early-stage kidney injury

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Magnetohydrodynamic slip flow and diffusion of a reactive solute past a permeable flat plate with suction

Krishnendu BHATTACHARYYA, G. C. LAYEK

《化学科学与工程前沿（英文）》 2011年第5卷第4期页码 471-476 doi: 10.1007/s11705-011-1130-z

摘要： The magnetohydrodynamic (MHD) boundary layer slip flow and solute transfer over a porous plate in the presence of a chemical reaction are investigated. The governing equations were transformed into self-similar ordinary differential equations by adopting the similarity transformation technique. Then the numerical solutions are obtained by a shooting technique using the fourth order Runge-Kutta method. The study reveals that due to the increase in the boundary slip, the concentration decreases and the velocity increases. On the other hand, with an increase in the magnetic field and mass suction, both boundary layer thicknesses decreased. As the Schmidt number and the reaction rate parameter increases, the concentration decreases and the mass transfer increases.

关键词： slip flow MHD boundary layer reactive solute diffusion flat plate suction/injection

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Molecular diffusion in ternary poly(vinyl alcohol) solutions

《化学科学与工程前沿（英文）》 2022年第16卷第6期页码 1003-1016 doi: 10.1007/s11705-021-2121-3

摘要： The diffusion kinetics of a molecular probe—rhodamine B—in ternary aqueous solutions containing poly(vinyl alcohol), glycerol, and surfactants was investigated using fluorescence correlation spectroscopy and dynamic light scattering. We show that the diffusion characteristics of rhodamine B in such complex systems is determined by a synergistic effect of molecular crowding and intermolecular interactions between chemical species. The presence of glycerol has no noticeable impact on rhodamine B diffusion at low concentration, but significantly slows down the diffusion of rhodamine B above 3.9% (w/v) due to a dominating steric inhibition effect. Furthermore, introducing surfactants (cationic/nonionic/anionic) to the system results in a decreased diffusion coefficient of the molecular probe. In solutions containing nonionic surfactant, this can be explained by an increased crowding effect. For ternary poly(vinyl alcohol) solutions containing cationic or anionic surfactant, surfactant–polymer and surfactant–rhodamine B interactions alongside the crowding effect of the molecules slow down the overall diffusivity of rhodamine B. The results advance our insight of molecular migration in a broad range of industrial complex formulations that incorporate multiple compounds, and highlight the importance of selecting the appropriate additives and surfactants in formulated products.

关键词： fluorescence correlation spectroscopy poly(vinyl alcohol) anomalous diffusion crowding effects dynamic light scattering binding effects rhodamine B

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Reaction kinetics and internal diffusion of Zhundong char gasification with CO

Yun Liu, Jiangyuan Qu, Xuehui Wu, Kai Zhang, Yuan Zhang

《化学科学与工程前沿（英文）》 2021年第15卷第2期页码 373-383 doi: 10.1007/s11705-020-1949-2

摘要： Mass transfer usually affects the rate of chemical reactions in coal. The effect of internal diffusion on char gasification with CO in the temperature range from 1123 K to 1273 K was investigated via thermo-gravimetric analysis and assessment of char morphology features. The results revealed that the effect of internal diffusion on the initial reaction rate was more significant with an increase of particle size, due to the concentration gradient of the gasification agent within the solid particles. In the early stage of gasification, the generation of new micropores and the opening of closed pores led to an increase in specific surface area. As the reaction proceeded, the openings were gradually expanded and the specific surface area continued to increase. However, with further reaction, disappearance of edge pores, melting and collapse of the pore structure led to a decrease in specific surface area. The intrinsic activation energy and reaction order based on the th-order model were 157.67 kJ∙mol and 0.36, respectively. Thus, temperature zones corresponding to chemical reaction and diffusion control were identified. Moreover, the calculated effectiveness factor provided a quantitative estimation of internal diffusion in the initial stage.

关键词： coal char CO₂ gasification internal diffusion pore evolution