A SIMPLIFIED REDUCED ORDER MODEL TO PREDICT PHASE CHANGE MATERIALS HEAT TRANSFER INCLUDING NATURAL CONVECTION

Phase change materials are widely used for heat transfer applications like thermal storage systems, electronic and batteries cooling, and generally heat exchangers. When such materials are in liquid phase, natural convection might arise, thus running computational analysis becomes long and difficult. Therefore, simplified reduced order models could be an option to reduce the computational effort obtaining reasonable melting front and temperatures evolution. In this paper, a simplified predictive model is presented. The phase change problem is modeled by using a fixed grid approach with an equivalent heat capacity replacing also the latent heat during phase change. With references to natural convection, this has been modeled by employing an effective thermal conductivity that accounts for convection effects via including a tuned Nusselt vs Rayleigh heat transfer correlation. Governing equations under the assumption of a uniform vertical wall temperature condition have been solved with a control volume in-house code. Results in terms of liquid fraction and temperature evolution have been compared with finite element CFD solutions showing a good agreement during the transient evolution. The present results can be then helpful for whom wants to study a phase change problem without invoking any CFD solvers for the complete Navier-Stokes equations, and it will be a first step for more comprehensive phase change models that account for other materials like extended surfaces, porous materials, nanoparticles, and so on.