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The "empty shell" potshell model type has by far the fastest turn
around time which is very convenient to be able to quickly
investigate potshell design alternatives. Unfortunately, its ability to
make accurate predictions outside of the narrow range of
conditions where it has been validated is very questionable.

The "almost empty shell" potshell model type is offering a much
wider applicability range as it will automatically adjust the internal
load as function of the grade of cathode blocks selected and of the
rigidity of the potshell structure. Still, by avoiding to simulate the
1000 days gradual sodium diffusion and gradual carbon swelling in
a transient solution, it offers an overnight turn-around time for a
very little loss of accuracy.

The "half empty shell" potshell model type is the most accurate
model type of the three presented because it incorporates all the
known physics of the cathode block sodium expansion phenomena
affecting the potshell deformation in addition to the thermal
expansion. Still, the accuracy of the third model type is not
absolute because even more complex phenomena could be added to
the model as discussed in [10] and [11] per example. In particular,
the complex behavior of the ramming paste in the big joint during
the preheat and early operation period, completely neglected in the
current study, would affect the predicted potshell displacement.

Yet, adding even more complex phenomena will further increase
the model turn-around time which at 1.2 CPU days is already
exceeding the overnight turn-around time that could be considered
as the practical upper limit for an efficient design tool, at least
when using a 64 bits dual cure Intel Centrino T9300 Dell Precision
M6300 computer as the number cruncher.

Finally, until the day where the turn-around time of the "half empty
shell" potshell model type would be reduced to mere minutes as it
will become maybe 20 years from now (after all it was 80 days on a
CRAY X-MP/24 supercomputer 20 years ago), it could be argued
that all three types of potshell models have their places in the
potshell designer toolbox as sometimes turn-around time matter
more than accuracy and sometimes not.

Acknowledgements

The author wishes to thanks Dr Daniel Richard of Hatch and Mr
Lalit Mishra of Dubal for their much needed assistance in using
ANSYS^® 11.0 thermo-mechanical features, especially in plastic

properties mode.

References

G. V. Asadi, M. Dupuis and I. Tabsh, "Shell Design Technique

Considering the Sodium Swelling Phenomena of Carbon
Cathode Blocks", in Proceedings of the 32nd Conference of
Metallurgists, CIM

, (1993), 125-130.

M. Dupuis, V. Bojarevics and J. Freibergs. "Demonstration

Thermo-Electric and MHD Mathematical Models of a 500 kA
Al Electrolysis cell", in Proceedings of the 42nd Conference on
Light Metals, CIM

, (2003), 3-20.

M. B. Rapoport and V. N. Samoilenko, "Deformation of

Cathode Blocks in Aluminium Reduction Cells during Process
of Electrolysis", in TsvetnyeMetally, (1957), vol 30, 44-51.

E. W. Dewing, "Longitudinal Stress in Carbon Lining Blocks

Due to Sodium Penetration", in Proceedings of TMS Light
Metals,