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Using ANSYS and CFX to Model Aluminum Reduction Cell since 1984 and Beyond
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includes the geometry of the cathode blocks themselves. As already briefly described in Reference 39, the
Dewing sodium expansion behavior of the cathode blocks is treated in ANSYSŪ as a "creep-like"
behavior. By definition, this means that it is required to solve that model in transient mode following the
build-up of the sodium concentration in the cathode blocks from start-up to around 1000 days of operation
where the cathode blocks get fully saturated in sodium. This way, the model computes the incremental
build-up of the strain-stress relationship due to the gradual and non-uniform carbon swelling generated
from the gradual increase in the sodium concentration in the cathode blocks and also to the gradual and
non-uniform restraining effect of the potshell on the cathode blocks sodium expansion. Of course, this
must be done using relatively small time steps hence the huge CPU time requirement.
Solving the "half empty shell" demo potshell model in plastic properties mode presented in Figure 25 took
103842 CPU seconds or 1.2 CPU days on the 64 bits dual core Intel Centrino T99300 Dell Precision
M6300 portable computer which is 3.8 times more than what was required to solve the "almost empty
shell" demo potshell model in plastic properties mode. It is interesting to note that the CRAY X-MP/24
would have required about 80 CPU days to solve the same model at 90 MFLOPS, which could explain why
Figure 1 of Reference 39 presents model results after 60 days of cathode life only!
2010: Fully coupled thermo-electro-mechanical anode and cathode
models
The author took advantage of the recent development of ANSYSŪ contact elements library to develop an
ANSYSŪ version 12.0 based fully coupled TEM anode stub hole design tool that is now available to the
whole aluminium industry through GeniSim Inc. That model is based on the usage of ANSYSŪ SOLID226
3D thermo-electro-mechanical second order element together with CONTA174 and TARGE170 thermo-
electro-mechanical contact pair elements. Furthermore, CONTA174 element supports the setup of a
pressure and temperature TCC (thermal contact conductance) and ECC (electrical contact conductance)
values through the %table% option.
The quarter stub hole model presented in Figure 26 solves in only around 4000 CPU seconds on a 64 bits
dual core Intel Centrino T 9300 Cell Precision M6300 portable computer running ANSYSŪ 12.0 version.
So this parametric ANSYSŪ based TEM anode stub hole model is a very efficient tool to study alternative
flutes design per example (Reference 40).
As for the TEM anode stub hole design tool developed and presented before (Reference 40), the TEM
cathode collector bar slot model is based on the usage of ANSYSŪ SOLID226 3D thermo-electro-
mechanical second order element together with CONTA174 and TARGE170 thermo-electro-mechanical
contact pair elements. CONTA174 element supports the setup of a pressure and temperature TCC (thermal
contact conductance) and ECC (electrical contact conductance) values through the %table% option.
The finer mesh quarter block model presented in Figure 27 solves in only around 5200 CPU seconds on a
64 bits dual core Intel Centrino T 9300 Cell Precision M6300 portable computer running ANSYSŪ 12.0
version. So this parametric ANSYSŪ based TEM collector bar slot model is a very efficient tool to study
alternative collector bar and collector bar slot design (Reference 41).
2011: What still remains to be done and when it will be done
As for past developments, the author believes that the rate of future model development will be mainly
dictated by the Moore law. As stated at the beginning, the ultimate goal as far as model development is
concerned is the development of a fully coupled multi-physics model of a full electrolysis cell. Why?
Simply because in an electrolysis cell many different interrelated types of physics are involved and all of
those interactions have a significant impact on the process:
1) The potshell must be mechanically designed so that it will not plastically deform under its thermal and
lining expansion pressure loading. Yet, that loading depends on the lining design, itself mostly dictated
by the thermo-electric behavior of the cell;