Thermal phenomena

In the last  decades, the cost of energy never stopped increasing and this tendency is not about to decrease. As a major consumer of electricity, aluminum producers had to adapt and take more account of the energetic efficiency of electrolysis cells, this is to say, the ratio between energy used and aluminum produced. Something certain is that much of the lost energy comes from the Joule effect generated by the current passing through the poorly conductive bath. Thus the distance between anodes and aluminum greatly influences the energetical cost of the production. Unfortunately it is known that reducing this distance tends to increase MHD instabilities and thus reduce the current efficiency.

A complete sudy of thermal effects seems essential to ensure optimal operation of the cells. On the other hand we must also consider the formation of solidified bath areas on the boundary of the cell that allows to protect the metal structure from the highly corrosive bath.

Within the Alucell software, the chair ASN developed a model for the thermal resolution (Heat equation) coupled with the MHD formulation (Maxwell for Joule effect and Navier-Stokes for temperature convection). With this model we can compute a stationary solution for the thermal problem, study the boundary flow, the formation of solidified zones and the influence of those on the Joule effect.

Hereafter, an example of stationary temperature (without convection) in a realistic cell (top view) and associated solidified areas.

To illustrate our thermoelectric simulations, here is an animation of the evolution of solidified bath areas and their interaction with the fluid velocity at the aluminum-bath interface.