Jiemin Zhou

Influence of alloy components on arc erosion morphology of Ag/MeO electrical contact materials

Abstract Arc erosion morphologies of Ag/MeO(10) electrical contact materials after 50000 operations under direct current of 19 V and 20 A and resistive load conditions were investigated using scanning electron microscope (SEM) and a 3D optical profiler (3DOP). The results indicated that 3DOP could supply clearer and more detailed arc erosion morphology information. Arc erosion resistance of Ag/SnO 2 (10) electrical contact material was the best and that of Ag/CuO(10) was the worst. Arc erosion morphology of Ag/MeO(10) electrical contact materials mainly included three different types. Arc erosion morphologies of Ag/ZnO(10) and Ag/SnO 2 (10) electrical contact materials were mainly liquid splash and evaporation, and those of Ag/CuO(10) and Ag/CdO(10) were mainly material transfer from anode to cathode. Arc erosion morphology of Ag/SnO 2 (6)In 2 O 3 (4) electrical contact materials included both liquid splash, evaporation and material transfer. In addition, the formation process and mechanism on arc erosion morphology of Ag/MeO(10) electrical contact materials were discussed.

Analysis and modeling of alumina dissolution based on heat and mass transfer

Abstract A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was used to calculate the size dissolution rate, dissolution time and mass of alumina dissolved employing commercial software and custom algorithm based on the shrinking sphere assumption. The effects of some convection and thermal condition parameters on the dissolution process were studied. The calculated results show that the decrease of alumina content or the increase of alumina diffusion coefficient is beneficial for the increase of size dissolution rate and the decrease of dissolution time of non-agglomerated particles. The increase of bath superheat or alumina preheating temperature results in the increase of size dissolution rate and the decrease of dissolution time of agglomerated particles. The calculated dissolution curve of alumina (mass fraction of alumina dissolved) for a 300 kA aluminum reduction cell is in well accordance with the experimental results. The analysis shows that the dissolution process of alumina can be divided into two distinct stages: the fast dissolution stage of non-agglomerated particles and the slow dissolution stage of agglomerated particles, with the dissolution time in the order of 10 and 100 s, respectively. The agglomerated particles were identified to be the most important factor limiting the dissolution process.

Simulation of Anode Bubble: Volume of Fluid Method

In an aluminum reduction cell, bubbles are generated on the anode surfaces. Before they get out of the bath, they linger over between gap of the anode and the cathode, which leads to additional voltage drop. The alumina concentration adjacent to the anode is also affected. How are the bubbles formed and what kinds of shape they have are the important issues. Numerical simulation can provide detailed information about bubbles. The volume of fluid model (VOF) was applied in the bubble simulation. The flow difference between different locations was presented.

Current Efficiency Predictive Model and Its Calibration and Validation

Current efficiency is one of the most important technical and economic parameters. Current efficiency loss is due to dissolved aluminum reacting with the anode bubbles by the back reaction, which is assumed to be responsible for the largest part of current efficiency loss in Hall-Heroult aluminum reduction cells. The magnetichydrodynamics flow in cells can be seen as a gas-liquid-liquid flow by neglecting the mina effect of alumina particles. An current efficiency predictive model (CEPM) was developed based on multiphase multicomponent flow. The model takes the flow in cells as a three-phase(the bath, the metal, and the anode bubbles) and multicomponent problem(the bath phase: bath species and dissolved Al species; the anode-bubble phase:CO2 and CO), which is able to incorporate the mechanism of current efficiency loss in cells. The model was calibrated by a 160kA cell and validated by a 300kA cell. This study provides a new approach for predicting current efficiency of aluminum reduction cells.

Numerical Simulation and Optimization of the Thermodynamic Process of the Molten Salt Furnace

In this paper, a numerical model of the molten salt furnace process was developed, by using computational fluid dynamics (CFD) technique and considering the gas flow, the combustion and the radiation heat transfer. The results demonstrate that the performances of the salt furnace could be improved by optimization using the numerical model. The temperatures along the circumference of the furnace coil and outside shell are quite even, and the deviant combustion phenomenon is not observed. A back-flow formed in the upper part of the furnace chamber enhances the circulation and the mixing of the gas and effectively stabilizes the combustion in the furnace. The behaviors of CO, CO2, NOx, and H2O are presented in terms of the gas flow, temperature distribution and volumetric concentration distribution. It is concluded that the furnace with the constant air flow rate of 15,500 Nm3/h and the guiding vane angle at 48–50 deg is optimized for the combustion effectiveness.

Computational Analysis of Thermal Process of a Regenerative Aluminum Melting Furnace

To understand melting behavior of a regenerative aluminum melting furnace, a computational fluid dynamics based on process model was developed and integrated with user-developed melting model, oxide loss model, burner reversing and burning capacity model. Simulations of melting process were made to model the flow and thermal phenomena in such a furnace. The rules of thermal process on melting behavior are obtained: Aluminum temperature increases slowly with melting time in solid-liquid zone, but rises faster when leaving solid-liquid phase lines. Furnace temperature first increases with melting time, then stepwise decreases, lastly periodically increases. Oxide weight parabolically increases with melting time. Aluminum temperature parabolically increases with oxide thickness. In early meltingstage, flue gas temperature reduces with liquid fraction, yet in later melting stage increases. Oxygen concentration in flue gas increases with liquid fraction in early melting stage yet remains constant in later melting stage.

A CFD‐PBM Coupled Model Predicting Anodic Bubble Size Distribution in Aluminum Reduction Cells

In order to understand more details of anodic bubble formation, coalescence and movement mechanism under the horizontal anode bottom, a population balance model (PBM) was used to calculate the anodic bubble size distribution (BSD) in aluminum reduction cells. The proposed PBM was numerically solved with a class method (CM) which has been provided in ANSYS FLUENT. A CFD-PBM coupled model that combines the PBM and CFD model was used to simulate more complex flow behavior with proper coalescence and breakage mechanism of anodic bubble. A modified k-e turbulence model was used to describe liquid phase turbulence in the simulation. The effects of current density, anode width and the presence of slots on the BSD have been investigated. In addition, the relative influence of the bath flow induced by the cell magneto-hydrodynamic (MHD) on the BSD is also discussed. The predicted BSD is in accordance with a series of literature experimental results.

Thermal and Electrical Analysis of the Anode

Thermal and electrical shocks are the main causes for the anode cracking, which results in severe cell disturbance and higher net carbon consumption. A parametrical finite element analysis (FEA) model is developed to simulate the thermal distribution of an anode after setting. The actual temperature and voltage drop of the anode was measured in industrial cell. The temperature and voltage drop of the anode were analyzed.

Numerical Simulation of the Thermodynamic Process of the Molten Salt Furnace

In this paper, a numerical model of the thermodynamic process was developed, by using CFD (software) technique and considering the gas flow, the diffused combustion and the radiative heat transfer in the molten salt furnace. This model aims to optimize the operating parameters. Simulation results demonstrate that the performances of the salt furnace can be improved by optimization. The temperatures along the fire wall circumference are quite even, and the deviant combustion phenomenon is not observed. A back-flow formed in the upper part of the furnace chamber enhances the circulation and the mixing of the gas, helping to effectively stabilize the combustion in the furnace. The behaviors of CO, CO2, NOx and H2O are presented in terms of the gas flow, temperature distribution and volumetric concentration distribution. The furnace with the constant air flow rate of 15500Nm3/h and the angle of guide vane at 48∼50 ° can increase the combustion effectiveness.Copyright

Workflow Simulation of TDSA Using ControlBuild Software

A dynamic model of the Tube Digester System in Alumina (TDSA) production was developed by using Matlab/Simulink package. A novel workflow simulation method based on Virtual Operating Environment (VOE) was proposed, and a prototype system based on a commercial control-build software was presented. In order to increase the reliability and visibility of simulations, animations demonstrating the simulation process were studied. Based on the workflow virtual operating environment, the simulation engine can impel the workflow running and deal with semi-automatic or manual activities automatically. The workflow simulation model of TDSA can be used to assess the performances of operating processes, diagnose the existing process and provide qualitative and quantitative analysis for the optional retrofit methods.© 2012 ASME