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Bateman metals improve Söderberg electrode pressure ring
Dr. B.J. Henning, Bateman Metals, South Africa

STAR-CD has recently been used by Bateman Metals to predict the cooling fluid flow and conjugate heat transfer in a new electrode pressure ring for Söderberg electrode applications.

The electrode pressure ring comprises segments cast from Aluminum Bronze, pinned together to form a cylinder. Passages are cast into each segment to enable cooling water to be circulated through the pressure ring assembly. The pressure ring applies a force to the contact shoes to engage the face of the shoe against the electrode casing, thereby ensuring that current is conducted from the furnace bus tubes into the electrode with minimum resistance. The contact shoe operates under arduous, high temperature conditions in close proximity to the pyrometallurgical process. Optimization of the heat dissipation capacity of the pressure ring is critical to ensure satisfactory service life. STAR-CD was used to evaluate the conjugate heat transfer capabilities of different designs.

The existing and proposed pressure ring elements were modeled to enable improvements to be evaluated. Both models were meshed using tetrahedral elements due to the complexity of the geometry, and up to one million cells were required for the proposed model to investigate the fine detail of the flow and heat transfer characteristics. The models and meshes were generated in other CAE packages, and were accurately and conveniently imported into STAR-CD for the numerical simulations.  
        

Fig 1: Surface model of the existing pressure ring design Fig 2: Surface model of the new pressure ring design

Heat flux boundary conditions were applied to the lower surface of the pressure ring, whilst fixed temperatures were specified for the balance of the aluminum bronze external surfaces. An inlet velocity was specified at the inlet ports of the water passages, and a pressure boundary specified at the outlets to enable the pressure drop characteristics of the designs to be estimated.

The velocity vector and isothermal contour plots produced by post processing of the simulation results were used to assess areas of stagnation/ re-circulation which indicate poor heat transfer capabilities. These zones are associated with high temperatures at the surface of the casting. High temperatures reduce the mechanical properties of the pressure ring material, and high temperature gradients make the castings vulnerable to cracking. The water passage configuration was modified to make the velocity profiles as uniform as possible, with commensurate reduction in hot spot formation.

The surface models of the existing- and new pressure ring designs are shown in figures 1 and 2.

The predicted steady state results for the relative pressure distribution through the existing- and new design water-cooling passages are shown in figures 3 and 4.
    

Fig 3: Pressure distribution through the existing pressure ring cooling water passages
Fig 4: Pressure distribution through the new pressure ring cooling water passages
                                                                                   
Fig 5: Surface temperature distribution for the existing aluminium bronze pressure ring
Fig 6: Surface temperature distribution for the new aluminium bronze pressure ring

The predicted steady state results for the surface temperature distribution on the existing- and new design water-cooling passages are shown in figures 5 and 6. Essential data comparisons between the existing- and new designs from the predicted CFD simulations are shown in Table 1.

For modeling purposes, CFD has provided a cost effective method of rapid prototyping the proposed changes prior to re-tooling and manufacture. Data will be collected from the operational equipment for simulation validation, and further design modification if necessary.

Table 1

In conclusion

  * STAR-CD allowed for the importation of complex tetrahedral meshes from other CAE environments
  * CFD enabled problem areas in the existing pressure ring design to be identified
  * The water-cooling passage configuration was changed based on the insight provided by the initial
      simulations
  * An improved design was obtained without costly field trials  

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