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Using ANSYS and CFX to Model Aluminum Reduction Cell since 1984 and Beyond
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The anode stud/cathode block cast iron connection system thus is a perfect example of fully coupled
thermo-electro-mechanic behavior. This complex behavior was successfully reproduced in a model by
Daniel Richard in his master study project. That model was then successfully used to improve the stud hole
design in order to minimize the voltage drop due to contact resistance (References 18 and 19).
2000: 3D thermo-electric full quarter cell model
The continuous increase of the computer power now allows not only to merge the anode to the cathode in a
cell slice model but also in a full quarter cell model (Reference 16, see Figure 13). The liquid zone can
even be included if the computation of the current density in that zone is required for MHD analysis
(Reference 7).
We are not yet at the point where we can plan to solve a full cell and external busbars thermo-electric
model on a US $2000 PC, but this time will come soon!
2001: 3D potroom ventilation model
The mixed convection air circulation pattern inside an aluminium smelter "potroom" building is rather hard
to reproduce in a mathematical model. As it was demonstrated previously (Reference 30), only the use of a
differential Reynolds flux turbulence model available in the CFX-4 commercial code led to the accurate
reproduction of the 2D flow pattern observed in a small physical model.
As the ventilation pattern in a modern smelter "potroom" building is truly three dimensional in nature, the
next logical step was to develop a 3D ventilation model to be able to carry out industrial applications. As
before, the model was developed using the CFX-4 commercial code in order to use the differential
Reynolds flux turbulence model that in 3D requires the solution of ten partial differential equations
(Reference 31).
For the presented mesh density, the model is made of 163,590 finite volumes. As the differential Reynolds
flux turbulence model is being used, there are a total of 15 partial differential equations that needs to be
solved at each node.
As the model is not converging with the default setting, the temperature has to be underrelaxed to ensure
smooth convergence. For that reason, the model required around 800 iterations to converge. Since each
iteration requires 22 CPU seconds on a PIII 800 mHz computer, the total convergence required 4.9 CPU
hours, see results in Figure 21.
2002: 3D half cell and external busbars thermo-electric model
Taking advantage of the increasing power of computers, it is now practical to consider building a 3D full
cell and external busbars thermo-electric model. In the present study, a 3D full cell quarter thermo-electric
model and a 3D cathode half plus liquids zone and busbars thermo-electric model have been developed and
solved using a PIII 800 MHz computer (Reference 26).
Developing a 3D full cell and external busbars thermo-electric model will constitute a step further towards
the development of a fully "multi-physic" unified aluminium reduction cell model.
We can see in Figure 13 the "complete" version of the 3D full cell quarter thermo-electric model. That
model is using 44,260 thermo-electric 3D elements for to mesh the anode rods and studs, the anode carbon
blocks, the cathodes blocks and the collector bars ands flexible. It is using 36,818 3D thermal only
elements to mesh the anode crust, ledge and cathode lining, 8853 2D thermal only elements to mesh the
cathode shell and 15165 3D electric only elements to mesh the liquid bath and metal.
The convergence of the ledge profile and hence the corresponding metal pad geometry is also part of the
problem solution. A PIII 800 MHz computer with 384 MEG of RAM memory and equipped with a 20 GB
SCSI hard disk took 52.48 CPU hours and 75.68 wall clock hours to compute the solution presented in
Figure 14.