09 Novembre – Thesis defense - Abraham Moreno Reyna
10 h Amphi 2 - ENSCBP (Pessac)
Modeling of heat storage by phase change of binary composition alloys submitted to a controlled cooling.
The thesis focuses on the numerical modeling of a binary alloy to simulate the phase change behavior for thermal energy storage and discharge application. It includes effects of cooling rate, solidification rate, segregation, free convection and undercooling. The aim is to optimize the material heat storage capacity. In the present work, the temperature range for which phase change occurs are estimated thanks to the phase diagram of a binary alloy and the CALPHAD methodology, that return the phases of an alloy, including isothermal transformation. The Gibbs energy minimization is computed in a homemade numerical code and gives the steady phases. For a given temperature range, the code supplies the heat discharge and the corresponding alloy composition for equilibrium and off equilibrium situations. In the present method, first, the system cooling rate gives the solidification rate. This latter leads to the relation between the global kinetics and the microstructure. From the local off-equilibrium model, that depends on the partition coefficient variation, and the operating cooling rate, the undercooling degree is predicted. With data from bibliography, numerical comparisons are carried out to ensure the relevance of our numerical code, and to identify the heat released during several materials phase change, including specific phenomena, such as undercooling and recalescence.