Kinetics of freezing and melting of encapsulated phase change materials with effective convection: Experiments and simulations

Abstract

Storage of thermal energy in packed beds of encapsulated phase change materials (PCM) is becoming nowadays a common strategy, but its modeling requires deep knowledge of the physical processes of heat transfer. In this work, the kinetics of melting and freezing of a well-studied PCM (water) has been modeled by simulations with an effective description for convection, and tested against experiments. In our setup, a single spherical nodule is placed in a bath, and cooled or heated by natural or forced convection. In the model, one parameter per fluid phase needs to be fixed, which we determine by fitting with experiments (for the bath fluid and PCM in the fluid phase). These two parameters are then used to study the kinetics of melting at different temperatures, kinetics of freezing, and the freezing and melting in cylinders of different aspect ratios. In all cases, the results from the model are compared with experiments. The agreement is quantitative, with accurate predictions of melting and freezing times (discrepancies below 15%), and temperature plateaux, both in natural and forced convection. Notably, this simulation method does not use the fluid velocity, speeding up the modeling and making it suitable for large scale simulations of thermal storage tanks.