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Using ANSYS and CFX to Model Aluminum Reduction Cell since 1984 and Beyond

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2) The potshell could also be designed for its ferro-magnetic shielding impact on the magnetic field, itself

affecting the cell MHD stability;

3) The potshell temperature and mechanical deformation change its ferro-magnetic shielding

characteristics;

4) The potshell deformation and the cathode blocks heaving/erosion affect the geometry of the cell cavity

which itself affects the local thickness of the metal pad;

5) The local variation of the metal pad thickness directly affects the local horizontal current density which

itself affects the cell MHD stability;

6) The shape of the cell cavity and the local variation of the metal pad thickness also affect the local

cathode blocks surface temperature and the potential for local sludge accumulation on the cathode
surface;

7) The local cathode block surface temperature and local sludge accumulation affect the potential of

forming hard alumina deposition on the cathode surface, itself affecting the local current density, in
turn affecting the MHD metal flow and MHD cell stability;

8) The cell thermo-electric design affects the ledge thickness which itself affects the horizontal current

density, in turn affecting the cell MHD stability;

9) The cell MHD stability affects the anode-cathode adjustment which itself affects the cell heat balance,

in turn affecting the ledge thickness.

Only a fully coupled thermo-electro-mechanico-magneto-hydro-dynamic model could be used as a design
tool in order to fully take into accounts all of those complex interactions. On the other hand, such a model
even if it could be available today, could not be used as a practical design tool as it would require far too
much computer resources to have a manageable turn around time. That is why the Moore law will continue
to be an important factor in future model development rate.

Step 1, 3D thermo-electro-magnetic full cell and external busbars
model:

The next step would be to remesh the potshell with 3D elements and mesh the air around the cell and
busbars in order to be able to solve the magnetic field. For that preprocessing step, it would be nice if
ANSYS could provide an automatic way to generate that air mesh. As example, the surface on the existing
mesh could be used to create a single volume and a single "air" volume could be generated by subtracting
that single "cell" volume from a bigger volume incorporating it.

Once the air mesh is available, there is no harm trying to solve the magnetic field using the solution of the
previous model as current source and the potshell temperature to define its ferro-magnetic property using
the above computer. If the problem could be solved on that computer in an acceptable turn around time, it
would represent a major step forward accomplished very rapidly. If not, we will simply have to wait for the
next generation computer!

Step 2, 3D electro-magneto-hydro-dynamic full cell and external
busbars model:

The next step may require coupling of ANSYS with a powerful CFD solver like CFX for solving the cell
MHD flow, which is very demanding. The CFD code must be able to solve an immiscible two liquid
phases MHD driven flow, which includes the solution of the position of an internal free interface between
the two liquids. In addition, the top liquid phase flow is also driven by the drag of bubble release in
addition to the MHD Lorentz body force.

Solving the above flow problem with a constant Lorentz body force field is already quite a challenge and
should already require a lot of computing resources. Unfortunately, that would be neglecting an important
coupling effect. As the bath-metal interface deforms, the shape of the anodes must be readjusted to keep the
anode cathode distance constant. This change of geometry will for sure affect the bubble release pattern.