Fenomeni di convezione naturale nei processi di solidificazione

Dottorato di ricerca in meccanica teorica ed applicata. 11. cicloConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Melting of a pure metal on a vertical wall: Numerical simulation

Melting of pure gallium in a bidimensional rectangular cavity with aspect ratio 1.4 is presented. The paper is focused on pattern formation in the fluid phase during the process of melting. The formation of a multiple cells structure has been found during the first stage of the transient, while a merging of the small recirculating cells into larger ones is observed during the following stage of the transient, generating a quite complex evolution of the flow pattern. To ensure the validity of the flow pattern evolution found, a deep mesh sensitivity analysis has been performed and repeated during the different phases of flow evolution. Three different meshes have been tested, the finest of those, assuming asunity the shorter vertical dimension, with a Dx=1/640 and a Dy=1/320. To optimize computational resources requests, an optimal solution strategy has been adopted, using different meshes during the various phases of the transient, depending on the size of the melted zone. Because of the large request of CPU time only one test case is presented and compared with available results at Ra=7x10^5, Pr=0.0216, and Ste=4.6x10^-2. Results show that only the use of a fine mesh allows the observation of the multicellular flowstructure described

Phase Change Problems With Free Convection: Fixed Grid Numerical Simulation

. A numerical and experimental study of unsteady natural convection during freezing of water is presented. The mathematical model for the numerical simulations is based on the enthalpy-porosity method in vorticity-velocity formulation, equations are discretised on a fixed grid by means of a finite volume technique. A fully implicit method has been adopted for the mass and momentum equations. Experiments are performed for water in a differentially heated cube surrounded by air. The experimental data for natural convection with freezing in the cavity are collected to create a reference for comparison with numerical results. The method of simultaneous measurement of the flow and temperature fields using liquid crystal tracers is used. It allows us to collect transient data on the interface position, and the temperature and velocity fields. In order to improve the capability of the numerical method to predict experimental results, a conjugate heat transfer problem was solve..