Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The purpose of this study is to investigate and describe the dissolution and heat transfer mechanisms of a cooled solid in a liquid medium to properly establish a clear parallel with the alumina dissolution in the aluminum electrolysis process. The Schlieren method was used to visualize the dissolution kinetics of a solid in a liquid medium. Blocks of salt were cooled with liquid nitrogen and subsequently immersed in liquid water. The experimental method used allows for the visualization of either small or important changes in the density of the water due to different temperature or salt concentration. Thus, it is possible to visualize the movement of the water by filming the inhomogeneities generated by the thermal and dissolution process. In addition, a secondary camera also films the sample with a grid background to directly show the dissolution by another method. This secondary camera is also used to confirm the presence of disintegration in the sample. The results of the observations clearly show that a downdraft appears as the salted water sinks to the bottom of the tank. Small disintegration of the salt block is also noticeable where these small chunks come off and sink to the bottom of the tank leaving a trail that clearly shows their dissolution. Similar observations are also discussed regarding the effect of the temperature differences in the system. With an adequate representation of the kinetics considered, this study can henceforth be used to improve the understanding of the electrolysis process while also serve as a tool that validates some physical aspects implemented in mathematical models used to reproduce the dissolution of alumina in cryolitic bath.