Influence of graphite and quartz addition on the thermo–physical properties of bentonite for sealing heat-generating radioactive waste

Bentonite is one of the most favored buffer materials for the deep geological disposal of waste in clay and granite formations all over the world. Buffer material, used to isolate heat emitting waste canisters, has to take up a strong heat load. This paper presents results of investigations on enhancing the heat conduction within the bentonite sealing. Admixtures of quartz and graphite accelerate the heat transfer into the host rock. Test samples consisting of different bentonite–quartz and bentonite–graphite mixtures were prepared. The thermal conductivity was determined as a function of admixture content, temperature, water content, and sample density within 35° to 140 °C at a uniaxial pressure of 2 MPa. The necessary conductivity could not be achieved with quartz, but the addition of graphite led to a suitable thermal conductivity. A set of equations was developed for the calculation of the thermal conductivity and the design of an engineered geotechnical barrier with heat conduction properties similar to those of the particular host rock.     

Transient computational fluid dynamics modeling of pervaporation separation of aromatic/aliphatic hydrocarbon mixtures using polymer composite membrane

Pervaporation (PV) separation of toluene/n‐heptane mixtures was studied experimentally and theoretically by means of a molecular surface engineering (MSE) polymer composite membrane. A comprehensive mathematical model was developed to predict unsteady state transport of toluene and n‐heptane (nC₇) through the membrane. Conservation equations including continuity, and heat transfer equations were solved using finite element method (FEM). Computational fluid dynamics (CFD) technique was applied to solve the model equations. The model was then verified with PV experimental data. The simulation results were in good agreement with the experimental data. The simulation results revealed that the proposed model could provide a general simulation of transport in the PV process. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

A new equation for predicting electrical conductivity of carbon‐filled polymer composites used for bipolar plates of fuel cells

In this article, a statistical‐thermodynamic formula based on a new approach has been developed to predict electrical conductivity of carbon‐filled composites used for bipolar plate of proton exchange membrane fuel cell. In this model, based on percolation threshold phenomenon, it is assumed that the relationship between electrical conductivity of composite and filler volume fraction follows a sigmoidal equation. Afterwards, the four effective factors on composite conductivity including filler electrical conductivity, filler aspect ratio, wettability, as well as interface contact resistance are replaced upon constant parameters of sigmoidal function. In order to test the model, some single‐filler composites have been manufactured by using the phenolic resin as binder and graphite (G), expanded graphite (EG), and carbon fiber (CF) as fillers. The fitting quality is measured by R‐square, adjusted R‐square, SSE, and RMSE parameters. The results showed that there is a noteworthy agreement between the model and the experimental data. Compared to the other models, this model can be used for more types of fillers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Simplified evaluation on hydraulic conductivities of sand–bentonite mixture backfill

Sand–bentonite mixtures are planned for use as backfill materials for high-level nuclear waste disposal in Japanese project. Sand–bentonite mixtures are attracting greater attention as backfill materials because they offer properties of very low permeability and high swelling. We must investigate the hydraulic properties by experiments and evaluate quantitatively the hydraulic-conductivities of sand–bentonite mixtures to design specifications, such as dry density and bentonite content, of backfill materials.For that purpose, this study investigated hydraulic conductivities at different bentonite contents and dry densities by experimentation. In addition, we discussed the relationship between hydraulic conductivity and bentonite content from the viewpoint of bentonite swelling in backfill voids. Furthermore, this study proposed simplified evaluation for hydraulic conductivity using a parameter proposed by the author: swelling volumetric strain of montmorillonite. This evaluation method can obtain hydraulic conductivity of backfill materials at various dry densities and bentonite contents. Therefore, this evaluation method can be used for designing bentonite content and compaction density to achieve very low permeability.     

A transient method for mass‐transfer characterization through supported zeolite membranes: Extension to two components

In a previous work (Courthial et al.) a transient state characterization method for zeolite supported membranes has been proposed and tested for single components in the Henry domain. An extension of the method to single components beyond the Henry domain and to binary mixtures is described. Since the method is based on experiments performed within the linear domain, the dynamic model previously developed for single components in the Henry domain is extended. The parameter estimation procedure that is described is based on a deep analysis of the model structure with respect to its structural identifiability properties. Some experimental results concerning pure n‐butane as well as isobutane/n‐butane mixtures transport through mordenite framework inverted (MFI)‐supported membranes are finally shown to illustrate the technique. © 2012 American Institute of Chemical Engineers AIChE J, 59: 959–970, 2013     

Modeling reaction kinetics of rigid polyurethane foaming process

A theoretical model was developed to simulate the polyurethane foaming process for a rigid foam. In the model, multiple ordinary differential equations were solved by MATLAB and the model was able to predict temperature profiles by inputting foam recipe information. This initial study on foam modeling focusses on reaction kinetic parameters that were fitted to experimental temperature data as a function of time. The modeling was able to accurately model temperature profiles of single‐polyol polyurethane formulations and was able to accurately predict temperature profiles of mixtures based on pure component kinetic parameters. A primary goal of this work is to expedite the ability to develop new foam formulations by simulation—especially for incorporation of new bio‐based polyols into formulations. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1131‐1138, 2013     

Simulation of a composite cathode in solid oxide fuel cells

Incorporating the mechanistic model for oxygen reduction at YSZ/LSM interface, a complete micro-model for YSZ/LSM composite cathode considering all forms of polarization was developed which established the interrelationship among the transport phenomena, electrochemical processes and the microstructure of the composite cathode. The exchange current densities of the rate-limiting steps used in the simulation were obtained by fitting the proposed mechanistic model to the DC polarization curves. Simulation was conducted to predict the optimal design parameters, e.g. cathode thickness, particle size, particle size ratio and YSZ volume fraction, for a LSM/YSZ composite cathode. Except for the YSZ volume fraction beyond the percolation thresholds, the predicted results seem to be in good agreement with the experimental and literature data. Incorporating with reliable experimental data, the model can be used as a tool to guide the design of high performance cathodes.     

Modeling of the mechanical properties of nanoparticle/polymer composites

A continuum-based elastic micromechanics model is developed for silica nanoparticle/polyimide composites with various nanoparticle/polyimide interfacial treatments. The model incorporates the molecular structures of the nanoparticle, polyimide, and interfacial regions, which are determined using a molecular modeling method that involves coarse-grained and reverse-mapping techniques. The micromechanics model includes an effective interface between the polyimide and nanoparticle with properties and dimensions that are determined using the results of molecular dynamics simulations. It is shown that the model can be used to predict the elastic properties of silica nanoparticle/polyimide composites for a large range of nanoparticle radii, 10-10,000 Å. For silica nanoparticle radii above 1000 Å, the predicted properties are equal to those predicted using the standard Mori-Tanaka micromechanical approach, which does not incorporate the molecular structure. It is also shown that the specific silica nanoparticle/polyimide interface conditions have a significant effect on the composite mechanical properties for nanoparticle radii below 1000 Å.     

High-pressure phase equilibria of systems carbon dioxide + n-eicosane and propane + n-eicosane

In this work we investigated the phase equilibrium behavior of the binary asymmetric systems propane (C3) + n-eicosane (C20) and carbon dioxide (CO₂) + n-eicosane (C20). We used a variable-volume view cell for obtaining fluid–fluid equilibrium (FFE), solid–fluid equilibrium (SFE) and solid–fluid–fluid equilibrium (SFFE) experimental data. We modeled the phase equilibria of both systems using the Peng–Robinson Equation of State for describing the fluid phases and an expression for the fugacity of pure solid n-eicosane with parameters fit to reproduce the pure n-eicosane melting line. We performed the phase equilibrium calculations by implementing path-following methods for tracking entire solid–fluid (SF) and solid–fluid–fluid (SFF) equilibrium curves for binary asymmetric mixtures. This made it possible to obtain complete isoplethic lines or complete three-phase equilibrium lines in single runs. Although the model is relatively simple, it is able to grasp the complex observed behavior for the systems studied here.     

单向复合材料弹性模量预测新式

根据复合材料单层的实际构造，提出了串并联组合模型，采用微观力学与宏观力学相结合的方法，推导出一组计算和复合材料弹性模量的新公式，其优点是：Ｅ１和ｖ１２，Ｅ２和Ｇ１２的计算式形式对称，结构简单，计算容易，物理意义明确，我们把由世界上许多著名学者提出的多组预测公式和本文导出式计算所得的结果与国内外已发表的硼／环氧、碳／环氧、玻璃／环氧复合材料的实验数据相比较，结果表明：导出式比其他公式精确，更有价值，     

Statistical simulation of aluminum agglomeration during combustion of heterogeneous condensed mixtures

A statistical model of aluminum agglomeration during combustion of solid composite rocket propellants is considered; the model describes the process dynamics, beginning from propellant heating in the combustion wave and ending by separation of agglomerates from the burning surface. An algorithm of computing the agglomeration process by the Monte Carlo method is proposed. A series of computations of aluminum agglomeration is performed; the density distribution functions for agglomerate sizes are derived; the dependence of the mean-mass size of agglomerates on the mean-mass size of ammonium-perchlorate particles is determined. The model proposed predicts power dependences of the mean-mass size of agglomerates on pressure and burning rate, which agrees with available experimental data.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 2, pp. 62–74, March–April, 2005.     

Kinetic modelling of the anaerobic digestion of wastewater derived from the pressing of orange rind produced in orange juice manufacturing

A simplified kinetic model for studying the anaerobic digestion of wastewater derived from the pressing of orange rind as a result of orange juice production was proposed on the basis of the experimental results obtained. The process was conducted in a laboratory-scale completely stirred tank reactor operating in batch mode at mesophilic temperature (35 °C), with COD loads in the range of 2–5 g COD. The following simplified three-step reaction scheme was proposed: (1) hydrolysis and conversion of complex organic compounds into intermediate products of lower molecular weight; (2) conversion of these intermediates to volatile fatty acids (VFA); and (3) methanization of the VFA by methanogenic microorganisms. A mathematical model based on four segregated differential equations was formulated assuming that a fraction of this substrate is non-biodegradable and the above-mentioned steps follow first-order kinetics. It was found that the kinetic constants corresponding to these three stages (K₀, K₁ and K₂) decreased markedly with the load added to the reactor, showing the occurrence of an inhibition process. In addition, it was observed that the methanogenic step was the slowest in the overall anaerobic process. Finally, the model was validated by comparing the theoretical curves obtained with the corresponding experimental data of organic matter, VFA and methane. The deviations obtained (less than 20%) in most cases demonstrated the suitability of the mathematical model proposed and suggested that the parameters obtained represent and predict the activity of the microorganisms involved in the anaerobic digestion process of this wastewater.     

Macroscopic model for multispecies ion-exchange kinetics

A model for multispecies ion-exchange kinetics based on the Nernst-Planck equation is suggested. It is analyzed in comparison with the “locally-determinate” model described by Hwang and Helfferich [1]. The model makes possible simple computation. The conditions for the occurrence of unusual kinetic curves with a maximum are clarified. The proposed model is developed for different types of kinetic problems and verified by the experimental investigation of a kinetics in ternary systems.     

Kinetic modelling of methylcyclohexane ring-opening over a HZSM-5 zeolite catalyst

A kinetic model is proposed in order to quantify product distribution in the ring-opening (using high hydrogen concentration in the reaction medium) of methylcyclohexane (MCH) over a catalyst based on HZSM-5 zeolite. The model is based on a reaction scheme proposed by Cerqueira et al. for methylcyclohexane cracking at atmospheric pressure, which has been modified in order to include the effect of hydrogen over the individual reaction steps. The experimental results used for estimating the kinetic constant were obtained in a fixed bed isothermal reactor in a wide range of conditions, i.e. 250–450 °C; WHSV = 0.5–10.5 h⁻¹ (τ = 0.095–2 g_cat h g_MCH⁻¹); pressure = 5–80 bar; H₂/MCH molar flow ratio = 4–79; conversion = 0–100%. The kinetic model proposed can be regarded as a basis for the proposal of models for ring-opening reactions of more complex naphthenic feedstock from a prior hydrogenation step involving aromatic refinery streams of secondary interest.     

Prediction of breakthrough curves for adsorption on activated carbon fibers in a fixed bed

A new model is proposed to describe the removal of volatile organic compounds (VOC) from a gas stream passing through a bed packed with activated carbon fibers (ACFs). Toluene was used as the test compound. Both pore diffusion and surface diffusion are considered in the model. The equilibrium behavior is shown to fit the Dubinin–Radushkevich isotherm with the values of parameters K and W₀ of 1.101 × 10⁻⁹ and 57.73 kg/m³, respectively. The experimental results show that this model can predict VOC breakthrough curve very well.     

复合材料层合板低速冲击承载能力的细观力学有限元模型

将复合材料细观力学桥联模型与有限元软件ABAQUS结合,用于分析层合板受低速冲击作用的极限承载能力.通过确定组分材料是否破坏来判断单层板是否破坏,对破坏后的单层实施一种常系数刚度衰减.将细观力学本构模型、针对组分材料的破坏判据以及刚度衰减模式编制成用户子程序VUMAT,为ABAQUS求解层合板的极限冲击响应提供一种自定义材料模型.只需要输入纤维和基体的材料参数、纤维体积含量等有限数据并且无须单层板的实验数据,就能顺利实施复合材料层合板结构的冲击承载能力分析.所计算的层合板的挠度-时间曲线以及横向冲击力-时间曲线与实验值吻合良好,说明本文的方法是有效的.     

Organoclays for soil remediation: Adsorption of 2,4-dichlorophenol on organoclay/aquifer material mixtures studied under static and flow conditions

A column material containing organophilic clay particles was developed for soil remediation. 2,4-dichlorophenol adsorption on aquifer material with an effective particle diameter d < 1 mm and various partially modified dioctadecyldimethylammonium–montmorillonite/aquifer material mixtures were studied under static and flow conditions. The 2,4-dichlorophenol adsorption on the aquifer material was negligible. On organoclay/aquifer material mixtures the adsorption capacity increased with increasing organoclay content and the adsorption isotherms could be fitted by the Freundlich equation. In columns filled with organoclay/aquifer material mixtures, the 2,4-dichlorophenol retardation increased with increasing organoclay content up to 1% (w / w). Above 1.5–2.0% (w / w) the permeability of the column material decreased. The HYDRUS_1D model, which solves the convection–dispersion equation for solute transport, was used in a forward and inverse mode to simulate 2,4-dichlorophenol breakthrough in the columns. The simulations revealed that 2,4-dichlorophenol transport exhibited an additional kinetic effect not observed in the batch experiments.     

Developing ramming compounds for monolithic linings in steel ladles

Conclusions It is possible to use natural loamy sands with a refractoriness about 1650°C and containing 2.5–4.5% Al₂O₃, and also mixtures of quartz sands and 15% fireclay for rammed linings of steel ladles applied with sand slinger. The relationship between the wear of these linings in service and the compounds concentrations of alkali metal oxides was determined in the research.A composition was developed for a compound based on pure quartz material (Ovruch quartzites) with an addition of 15% fireclay. Production of the compounds has started at the Krasnogorov Refractories Plant. The use of the new compounds has increased the life of 100-ton ladles at the Dzerzhinskii Factory from 12 to 18–20 pourings.Translated from Ogneupory, No. 1, pp. 6–10, January, 1979.     

Bubbling fluidization of biomass and sand binary mixtures: Minimum fluidization velocity and particle segregation

Understanding the minimum fluidization velocity of biomass and sand mixtures is fundamental to ensuring the optimal performance of fluidized beds in a thermo-conversional process, such as fast pyrolysis. The present work aimed to determine the minimum fluidization velocity of binary mixtures using the characteristic diagram of pressure drop in the bed and to develop an experimental correlation for the minimum fluidization velocity of biomass and sand mixtures. Three types of biomass (sweet sorghum bagasse, waste tobacco and soybean hulls) and four sands with different sizes were investigated. The results showed that the fluid dynamic behavior of binary mixtures is directly related to the biomass size and shape. For sweet sorghum bagasse (more irregular particles), higher biomass percentages led to lower minimum fluidization velocities, which differed from the behaviors observed for waste tobacco and soybean hulls. The diameter ratio inert/biomass effectively influenced the segregation, with a higher ratio causing more pronounced bed segregation. A good fluidization regime (with little segregation) for biomass and sand mixtures was obtained using the smallest sand (d₅₀ = 0.35). Considering the studied operating conditions, the proposed correlation can be used satisfactorily to predict the minimum fluidization velocities for mixtures of biomass and sand in fluidized beds.