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ABSTRACT
A model for predicting anode cover behavior inside aluminum electrolysis cells is presented. The model predicts the transformation of anode cover material into a solid crust, the melting/solidification of the bath and crust, and the heat fluxes escaping the anode cover. The model is validated with experimental data taken on industrial electrolysis cells. The temperature and positions of the top crust, the heat flux escaping the anode cover, and the height of the cavity are presented, along with the model predictions. The effect of bath temperature on the crust formation is further investigated. Results show that the bath temperature can greatly enhance the rate of crust formation.
Nomenclature
| A | = | frequency factor [s−1] |
| ACM | = | anode cover material |
| ASD | = | anode to sidewall distance [m] |
| As | = | cross section of the anode or stubs [m2] |
| CA | = | concentration of reactant A [mol/l] |
| CFD | = | Computational Fluid Dynamics |
| Cp | = | specific heat [J/kg · K] |
| CR | = | cryolite ratio |
| dt | = | time step [s] |
| dx | = | space step [m] |
| dy | = | space step [m] |
| Ea | = | energy of activation [J/mol] |
| f | = | liquid fraction |
| h | = | heat transfer coefficient [W/m2 · K] |
| I | = | electrical current [A] |
| k | = | thermal conductivity [W/m · K] |
| kA | = | reaction rate constant [s−1] |
| n | = | number of moles [mol] |
| = | thermo-electric Joule effect [W/m3] | |
| q″ | = | heat flux [W/m2] |
| R | = | universal gaz constant [J/mol · K] |
| t | = | time [s] |
| T | = | temperature [K] |
| V | = | volume [m3] |
| x | = | space direction [m] |
| X | = | conversion |
| y | = | space direction [m] |
| α | = | thermophysical properties [kg/m3, W/m · K, J/kg · K, J/kg] |
| δH | = | volumetric enthalpy change [J/m3] |
| λ | = | heat of fusion [J/kg] |
| ρ | = | density [kg/m3] |
| ρΩ | = | electrical resistivity [Ω · m] |
| Ω | = | boundary |
| Subscripts | = | |
| ∞ | = | ambient |
| liq | = | liquidus |
| liquid | = | liquid state |
| 0 | = | initial |
| sol | = | solidus |
| solid | = | solid state |
Nomenclature
| A | = | frequency factor [s−1] |
| ACM | = | anode cover material |
| ASD | = | anode to sidewall distance [m] |
| As | = | cross section of the anode or stubs [m2] |
| CA | = | concentration of reactant A [mol/l] |
| CFD | = | Computational Fluid Dynamics |
| Cp | = | specific heat [J/kg · K] |
| CR | = | cryolite ratio |
| dt | = | time step [s] |
| dx | = | space step [m] |
| dy | = | space step [m] |
| Ea | = | energy of activation [J/mol] |
| f | = | liquid fraction |
| h | = | heat transfer coefficient [W/m2 · K] |
| I | = | electrical current [A] |
| k | = | thermal conductivity [W/m · K] |
| kA | = | reaction rate constant [s−1] |
| n | = | number of moles [mol] |
| = | thermo-electric Joule effect [W/m3] | |
| q″ | = | heat flux [W/m2] |
| R | = | universal gaz constant [J/mol · K] |
| t | = | time [s] |
| T | = | temperature [K] |
| V | = | volume [m3] |
| x | = | space direction [m] |
| X | = | conversion |
| y | = | space direction [m] |
| α | = | thermophysical properties [kg/m3, W/m · K, J/kg · K, J/kg] |
| δH | = | volumetric enthalpy change [J/m3] |
| λ | = | heat of fusion [J/kg] |
| ρ | = | density [kg/m3] |
| ρΩ | = | electrical resistivity [Ω · m] |
| Ω | = | boundary |
| Subscripts | = | |
| ∞ | = | ambient |
| liq | = | liquidus |
| liquid | = | liquid state |
| 0 | = | initial |
| sol | = | solidus |
| solid | = | solid state |
Acknowledgments
The authors would like to thank the CRDA reduction technicians team and the personnel of Usine Grande-Baie for their valuable help during the course of the measurement campaigns.