Orientation of the fiber suspending in the flow through a tube containing a sphere

Fiber suspensions flow through a tube containing a sphere in the dilute and concentrated regimes is simulated numerically with the Lattice Boltzmann Method (LBM). The numerical results of fiber orientation distribution based on a statistical scheme are obtained and agree qualitatively with the experimental ones for the flow through a parallel plate channel containing a cylinder. The results show that the sphere in the tube results in a change in the fiber orientation distribution downstream of the sphere along the flow and transverse directions. The influences of the sphere on the fiber orientation distribution are more significant for the concentrated suspensions than for the dilute one. The effect of the initial fiber orientations on the fiber orientation distribution is significant upstream of the sphere but small downstream of the sphere.     

Numerical simulation of motion of rigid spherical particles in a rotating tumbler with an inner wavelike surface

The present work is a numerical simulation of motion of rigid spherical particles within a 2-D tumbler with an inner wavelike surface. The rotation of the tumbler is simulated as a traveling sine wave around a circle. The discrete element method (DEM, a hard sphere approach) is used. The particle-wall interactions are taken into account in a changed numerical approach of hard sphere model. The effects of two basic factors of the rotating velocity (phase velocity) and the wave numbers are separately investigated. A simple but useful method for cluster identification is provided and used. The energy-based analysis of particle clusters and the motion pattern study indicate the existence of a pulsed variation in the kinetic energy of the clusters at low wave numbers and a cyclic bulk motion of the clusters at high wave numbers. The necessary conditions for the pulsed variation of motion of particle clusters at low wave number are analyzed and a mode for industrial application, e.g. coal grinding process in power plant, is demonstrated.     

Geometrical modeling of granular structures in two and three dimensions. Application to nanostructures

A granular structure can be modeled by a parallelepiped containing spherical balls in three dimensions or by a rectangle filled with disks in two dimensions. These grains (spherical balls or disks) are separated by interfaces called grain boundaries and their size correspond to a size distribution, which is obtained experimentally. The geometrical modeling of such a structure consists in determining the repartition of the set of disjoint grains according to these specifications. In this paper, a new constructive algorithm based on an advancing‐front approach, usually used in the context of mesh generation, is proposed. This algorithm is nearly linear in complexity, robust and fast in both two and three dimensions. Enhancements in computing time and density are observed and reported via comparisons with existing methods. Moreover, we propose a method to transform spherical balls (disks) into polyhedral (polygonal) cells similar to the real grain shapes. Examples of nanostructure modeling in two and three dimensions are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

水处理污泥陶粒的制备及其对重金属的固定

以湿态水处理污泥作为主要原料,混合粉煤灰和集料尾泥制备了陶粒,陶粒烧成过程模拟了回转窑工况条件。结果表明:当污泥掺入量较高时,污泥中有机成分的高温分解使陶粒坯体有较强的烧胀作用。当陶粒坯体中污泥质量含量为50%、粉煤灰和集料尾泥分别为25%时,1040℃短时烧结后的陶粒样品具有较为理想的轻集料性能,其堆积密度为760 kg/m3,筒压强度为5.2 MPa。浸出实验表明:随着污泥掺量的增加,从陶粒中浸出重金属离子量的增加幅度较小。这说明陶粒结构对污泥中的重金属有较强的稳定和固定作用,污泥陶粒的使用不会对环境造成二次污染。     

Preparation and properties of proton exchange membranes based-on Nafion and phosphonic acid-functionalized hollow silica spheres

Vinyl functionalized hollow silica spheres (HSSs) were prepared via a template method and surface modification thereafter. Poly(vinylbenzyl phosphonic acid) (PVBPA) grafted HSSs (HPSSs) were prepared via emulsion polymerization of diisopropyl p-vinylbenzyl phosphonate (DIPVBP) on the surface of HSSs, and hydrolysis thereafter. The chemical structure and morphology of HPSSs were characterized by FTIR and TEM. A series of proton exchange membranes based-on Nafion^®212 and HPSSs were prepared via solution casting. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and chemical oxidative stability of the composite membranes were investigated. The addition of HPSSs in Nafion^® membranes can improve the water retentivity of the composite membranes. The composite membranes with HPSSs exhibit higher water uptake and proton conductivity than that of the recast Nafion^® membranes. The water uptake and the proton conductivity of the composite membranes increase with increasing HPSSs loading. With the higher water retentivity, the membranes exhibit high proton conductivity at high temperature (1.6 × 10⁻¹ S cm⁻¹ at 125 °C).     

Catalyst-free growth of large scale nitrogen-doped carbon spheres as efficient electrocatalysts for oxygen reduction in alkaline medium

Nitrogen-doped carbon spheres (NCS) are synthesized by directly pyrolyzing a nebulized solution of xylene and ethylenediamine via a spray pyrolysis method, without using a catalyst. X-ray photoelectron spectroscopy (XPS) measurements confirm that the NCS only contain C, N and O. The electrocatalytic performances show that the NCS exhibit a high catalytic activity, long-term stability, and an excellent methanol tolerance for the oxygen reduction reaction (ORR) in an alkaline medium. This study successfully develops a new non-precious metal catalyst, which exhibits an excellent electrocatalytic performance, using a simple, cost-effective and scalable method. It also provides an increased fundamental understanding in the origins of ORR activity enhancements using N-doped carbon materials.     

The velocity of movement of isotherms near the thermal center of a cooled body

The behavior of isotherms near the thermal center of a cooled body has been considered. It is shown that closer to the thermal center the velocity of movement of isotherms increases sharply. An expression is obtained that describes the behavior of the velocity of movement of isotherms near the center of bodies of simple shapes (plate, infinite cylinder, rod of square cross section, sphere, and cube). Quantitatively the behavior of the velocity depends on the thermal diffusivity of the medium and the geometric form of the body but is independent of the absolute magnitude of the isotherms, body dimensions, and of the cooling inetnsity. The property indicated is typical of the processes described by parabolic-type equations. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 391–397, March–April, 2009.     

矿井直流电法超前预报球体构造的初步理论及沙槽实验研究

针对矿井直流电法掘进超前探测技术理论发展不够完善的现状,建立了独头巷道掘进面前方存在球体溶洞时的超前探测数学模型,发展了预报球体溶洞的超前探测理论,探讨了溶洞至掘进面距离、溶洞半径、埋深等参数与视电阻率异常的联系,给出了相应理论曲线或经验公式,并采用沙槽模拟实验对理论进行验证,对完善超前探测的资料解释技术,提高预报准确度具有指导意义.     

Magnetic Interaction Force and a Couple on a Superconducting Sphere in an Arbitrary Dipole Field

The calculation of the magnetostatic potential and levitation force due to a point magnetic dipole placed in front of a superconducting sphere in the Meissner state is readdressed. Closed-form analytical expression for the scalar potential function that yields the image system for an arbitrarily oriented magnetic dipole located in the vicinity of a superconducting sphere is given. Analytic expression for the lifting or levitation force acting on the sphere is extracted from the solution for a general dipole. A special case of our expression where the initial magnetic dipole makes an angle with the z-axis is derived. Our expression for the force in this particular case shows that a recently obtained result (J. Supercond. Nov. Magn. 21:93–96, 2008) for an arbitrary dipole is incorrect. A brief discussion of another erroneous result (J. Supercond. Nov. Magn. 15:257–262, 2002) for a transverse/tangential dipole–sphere configuration, corrected elsewhere recently, is reproduced. Correct expressions for the interaction energy with some limiting cases are also provided. The result derived here demonstrates that the value of the levitation force for a dipole that makes an angle with z-axis lies between the values for a radial dipole–sphere and transverse dipole–sphere configurations providing upper and lower bounds. It is found that for a magnetic dipole making an angle with z-axis, there exits a second force component along the negative y-direction, which influences a couple acting on the superconducting sphere. It is also shown that the couple is proportional to the second force component and that both the couple and second force components vanish for a radial dipole–sphere and transverse dipole–sphere configurations, respectively. These results appear to be new and have not had received due attention in the context of superconductivity.