优质矾土熟料生产中的原料均化过程

原料的均化过程是指矿山开采到煅烧之前的各主要环节。它包括矿山搭配开采运输；预均化与贮存；磨细混练压球；各料仓贮放、干燥等工序．承担均化任务量最大的是原料预均化，约占总量的７０％～８０％。原料预均化最优方式为长形料仓式原料预均化库。它具有投资低、占地面积小、作业条件好、粉尘少、均化效果高等优点．     

Multi-scale solid oxide fuel cell materials modeling

Performance and degradation of fuel cell components are discussed in a multi-scale framework in this paper. Electrochemical reactions in a solid oxide fuel cell occur simultaneously as charge and gas pass through the anode, electrolyte, and cathode to produce electric power. Since fuel cells typically operate at high temperatures for long periods of time, performance degradation due to aging of the fuel cell materials should be examined. This phenomenon is treated in a multi-scale framework by considering how microstructure evolution affects the performance at the macro-scale. Mass and charge conservation equations and electrochemical kinetic equations are solved to predict the overall cell performance using the local properties calculated at the micro-scale. Separately, the microstructures assigned to the macroscopic integration points are evolved via the Cahn–Hilliard equation using an experimentally calibrated kinetic parameter. The effective properties of the evolving microstructure are obtained by homogenization and incorporated in the macro-scale calculation. The proposed model is applied to a solid oxide fuel cell system with a nickel/yttria stabilized zirconia (Ni/YSZ) cermet anode. Our model predicts performance degradation after extended hours of operation related to nickel particle coarsening and the resulting decrease in triple phase boundary (TPB) density of the anode material. The investigation of the microstructural effects on TPB density suggests that using Ni and YSZ particles of similar size may retard performance degradation due to anode aging.     

Numerical and analytical effective elastic properties of degraded cement pastes

Cement pastes are heterogeneous materials composed of hydrates, anhydrous products and pores of various shapes. They are generally characterized by a high particle concentration and phase contrasts, in particular in the case of degraded materials which exhibit important porosity. This paper compares the performance of several classical effective medium approximation schemes (Mori–Tanaka, Zheng-Du, self-consistent) through their ability to estimate the mechanical parameters of cement paste samples obtained numerically. For this purpose, finite element simulations are performed on 3D structures to compute for each sample accurate values of these mechanical properties. For these simulations, the cement paste is considered as a matrix of C–S–H in which are embedded inclusions of anhydrous, hydration products, and pores. In order to evaluate the importance of the particle shape, two types of samples are generated, one with only spherical inclusions and the other containing both spherical and prismatic particles. Simulations with three perpendicular loading directions and both uniform and mixed boundary conditions are performed in order to verify that the dispersion in the computed elastic moduli is low, or equivalently that the generated structures are close to representative volume elements (RVEs). It is shown that the considered effective medium approximation schemes, except the self-consistent one, provide relatively good estimations of the overall mechanical parameters when compared to simulation results, including when both particle volume fraction and phase contrast are high. The analytical methods taking into account the particle shapes also give estimates close to the corresponding numerical simulations, the latter confirming the influence of the particle form.     

Derivation of the localization and homogenization conditions for electro-mechanically coupled problems

The challenges in high-performance mechatronics and micromechatronics are the modeling, analysis and design of electro-mechanical systems. Piezoceramics are the prototype of materials which exhibit characteristic electro-mechanical coupling effects used in a wide range of industrial applications. In complex designs of piezoceramic devices concentrations of stresses and electric field occur, which may lead to nonlinear electro-mechanical responses, typical for the large signal range. The challenge in the field of ferroelectric ceramics is the modeling of the complicated interactions between electrical and mechanical quantities on the macroscale, which are caused by switching processes on the microscale. In this paper we derive the basic equations for a possible direct two-scale homogenization procedure of electro-mechanically coupled boundary value problems.     

Numerical modeling of electrochemical–mechanical interactions in lithium polymer batteries

This paper presents a multi-scale finite element approach for lithium batteries to study electrochemical–mechanical interaction phenomena at macro- and micro-scales. The battery model consists of a lithium foil anode, a separator, and a porous cathode that includes solid active materials and a liquid electrolyte. We develop a multi-scale approach to analyze the surface kinetics and electrochemical–mechanical phenomena within a single spherical particle of the active material. Homogenization techniques relate parameters in the micro-scale particle model to those in the macro-scale model describing the lithium ion transport, electric potentials and mechanical response based on porous electrode theory.     

Asymptotic expansion homogenization for simulating progressive damage of 3D braided composites

In order to study tensile strength of 3D braided composites in the microscope view, non-linear progressive damages under tensile loading steps are conducted in this article. Micro-stress is simulated firstly by the method of Asymptotic Expansion Homogenization (AEH) combined with finite-element analysis. A criterion is approached to determine damage and its mode of each element, and stiffness degradation is implemented for the damaged elements with geometric damage theory. Furthermore, the tensile strengths are predicted from calculated stress–strain curves. From simulation, the damage mode for small braiding angle and large braiding angle is different at all. More damage elements are observed in face cell than in body cell. The tensile strength decreases with increase of braiding angle, but the fracture strain has different development. It is verified that 3D braided composites with small braiding angle have better strength but poorer ductility than the composites with large braiding angle.     

CFD prediction of fluid flow and mixing in stirred tanks: Numerical issues about the RANS simulations

This work is aimed at verifying the effect of numerical issues on the RANS-based predictions of single phase stirred tanks. In particular, the effect of grid size and discretization schemes on global parameters, mean velocity, turbulent dissipation rate and homogenization is considered. Although contradictory results have been reported so far on the capability of RANS methods in fluid mixing, the most widely accepted conclusion is that adequate values are generally to be expected for the predicted mean flow quantities, while much less confidence must be put on the calculated turbulent quantities and related phenomena. The results obtained in this work partially revise this last statement and demonstrate that firm conclusions on the limits of RANS simulations can be drawn only after careful verification of numerical uncertainties. The simulation results are discussed and compared to the literature experimental data and to original passive tracer homogenization curves determined with planar laser induced fluorescence.     

Hydrodynamics Characterization of an Ellipse Gate Impeller by Experimental and Numerical Studies

Hydrodynamics characteristics like flow pattern, shear rate distribution, power consumption, axial pumping capacity, mixing time, and mixing efficiency of an ellipse gate (EG) impeller were investigated by experimental and numerical methods. The numerical simulation results were validated by experimental data of power consumption and mixing time. Results indicate that the axial pumping number of the EG impeller is larger than that of any other reported large‐scale impeller under laminar regime, and that the shear rate formed by this impeller is less sensitive to Reynolds numbers. In‐depth analysis reveals the different function of each part of the EG impeller under different flow regimes. This impeller provides an almost similar mixing efficiency like the double‐helical ribbon impeller under laminar regime, but much higher mixing efficiency both under transitional and turbulent flow regimes.     

HOMOGENIZATION RESULTS FOR ENZYME CATALYZED REACTIONS THROUGH POROUS MEDIA

The aim of this article is to study the effective behavior of the solution of a nonlinear problem arising in the modelling of enzyme catalyzed reactions through the exterior of a domain containing periodically distributed reactive solid obstacles,with period ε.The asymptotic behavior of the solution of such a problem is governed by a new elliptic boundary-value problem,with an extra zero-order term that captures the effect of the enzymatic reactions.