Dynamic self-adaptive ANP algorithm and its application to electric field simulation of aluminum reduction cell

Region partition(RP) is the key technique to the finite element parallel computing(FEPC),and its performance has a decisive influence on the entire process of analysis and computation.The performance evaluation index of RP method for the three-dimensional finite element model(FEM) has been given.By taking the electric field of aluminum reduction cell(ARC) as the research object,the performance of two classical RP methods,which are Al-NASRA and NGUYEN partition(ANP) algorithm and the multi-level partition(MLP) method,has been analyzed and compared.The comparison results indicate a sound performance of ANP algorithm,but to large-scale models,the computing time of ANP algorithm increases notably.This is because the ANP algorithm determines only one node based on the minimum weight and just adds the elements connected to the node into the sub-region during each iteration.To obtain the satisfied speed and the precision,an improved dynamic self-adaptive ANP(DSA-ANP) algorithm has been proposed.With consideration of model scale,complexity and sub-RP stage,the improved algorithm adaptively determines the number of nodes and selects those nodes with small enough weight,and then dynamically adds these connected elements.The proposed algorithm has been applied to the finite element analysis(FEA) of the electric field simulation of ARC.Compared with the traditional ANP algorithm,the computational efficiency of the proposed algorithm has been shortened approximately from 260 s to 13 s.This proves the superiority of the improved algorithm on computing time performance.

Aluminum Reduction and Nitridation of Bauxite

The application of bauxite with low Al2O3 content has been studied in this paper and β-SiAlON has been obtained from two kinds of bauxites （Al2O3 content 68.08 mass% and 46.30 mass% respectively） by aluminum reduction and nitridation method. The sequence of reactions has been studied using thermal analysis （TG-DTA）, X-ray diffraction （XRD） analysis and scanning electron microscopy （SEM） with EDS. Compared with carbon thermal reduction and nitridation of aluminosilicates employed presently, the reaction in the system of bauxite-Al-N2 occurs at lower temperature. β-SiAlON appears as one of the main products from 1573K and exists stably in the range of the present experimental temperature. The microstructure of β-SiAlON obtained at 1773 K is short column with 5-10μm observed by SEM.

THE NUMERICAL SIMULATION OF FLOW IN ALUMINUM REDUCTION CELLS

The electromagnetic force causes a circulation of both cryolite and the metal in the aluminum reduction cells. This motion has the effect of reducing the current efficiency of the cell, and increases the distance between the an- ode and the cathode. Using the time-averaged Navier-Stokes equations and the K-e model of turbulence this paper numerically calculated the distributions of velocities, pressure, turbulent kinetic energy in the cells and deforma- tion of the interface of cryolite and metal. These results may be used to control the process of production and to improve the design of the cells.

Modeling of Three-Phase Flow and Interface Deformation of Metal/Bath in Aluminum Reduction Cell With Cathode Protrusion

Stabilizing the interface wave of the molten aluminum(metal)-electrolyte(bath)is beneficial to shorten the anode-cathode distance(ACD)which is critical to the energy saving.A coupled mathematical model was developed to study the impact of the novel cathode protrusion on the molten fluid motion as well as the metal-bath interface deformation.The molten fluid motion in the aluminum reduction ceils is under the combined effect of the electro-magnetic forces(EMFs)and the gas bubbles generated at the anode.A transient inhomogeneous three-phase model(metal-bath-gas bubble)was established in order to calculate more accurate.The results indicate that the metal-bath interface deformation can be reduced significantly by the novel cathode protrusion which is beneficial to the electric energy saving.Besides,The EMFs decreases as a result of the optimizing of the magnetic field due to the novel cathode convex which is an important driving force for the deformation of the interface.In addition,large vortex in the metal flow field is break up into the small vortex by the cathode protrusion and then dissipated due to the viscous force and the hindering effect of the cathode protrusion.The quantity of the vortex as well as the strength of the vortex reduces significantly in the reduction cell with novel cathode protrusion.

Colloidal Alumina-bonded TiB_2 Coating on Cathode Carbon Blocks in Aluminum Cells

Self-propagating high-temperature synthesis (SHS) with reduction process was used to fabricate TiB2 powder from TiO2-B2O3-Mg system. The colloidal alumina-bonded TiB2 paste was prepared and coated on the cathode carbon blocks. Various properties of the baked paste such as the corrosive resistance, thermal expansion and wettability were tested. Experimental results showed that the colloidal alumina-bonded TiB2 coating could be well wetted by liquid aluminum; and the thermal expansion coefficient of the coated material was 5.8x10(-6) degreesC(-1) at 20-1000 degreesC, which was close to that of the traditional anthracite block cathode (4x10(-6) degreesC(-1)); the electrical resistivity was 8 mu Omega (.)m at 900 degreesC when the content of alumina in the coated material was about 9% in mass fraction. In addition, some other good results such as sodium resistance were also reported.

COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.

Microwave absorption of aluminum/hydrogen treated titanium dioxide nanoparticles

Interactions between incident electromagnetic energy and matter are of critical importance for numerous civil and military applications such as photocatalysis,solar cells,optics,radar detection,communications,information processing and transport et al.Traditional mechanisms for such interactions in the microwave frequency mainly rely on dipole rotations and magnetic domain resonance.In this study,we present the first report of the microwave absorption of Al/H2 treated TiO_(2) nanoparticles,where the A_(l)/H_(2) treatment not only induces structural and optical property changes,but also largely improves the microwave absorption performance of TiO_(2) nanoparticles.Moreover,the frequency of the microwave absorption can be finely controlled with the treatment temperature,and the absorption efficiency can reach optimal values with a careful temperature tuning.A large reflection loss of
58.02 dB has been demonstrated with 3.1mm TiO_(2) coating when the treating temperature is 700℃.The high efficiency of microwave absorption is most likely linked to the disordering-induced property changes in the materials.Along with the increased microwave absorption properties are largely increased visiblelight and IR absorptions,and enhanced electrical conductivity and reduced skin-depth,which is likely related to the interfacial defects within the TiO_(2) nanoparticles caused by the Al/H2 treatment.