Crystallization of supercooled spherical nodules in a flow

The general context of this work concerns the latent heat storage (cold storage) by encapsulated spherical nodules of 7.7 cm in diameter containing a Phase Change Material (PCM) and filling a cylindrical tank (about 2500 nodules per m³). During the storage process, a cold heat transfer liquid flows through the tank to crystallize the PCM inside the nodules. The stored energy is released when a hotter heat transfer liquid flows through the tank to induce the melting of the PCM. As the velocity in the tank is relatively small (a few mm·s⁻¹), natural convection is expected on the coolant when the latent heat is released at the crystallization of the PCM. The present study concerns a single nodule surrounded by a flowing heat transfer liquid at a temperature T_C lower than the melting temperature T_F. This text presents an enthalpic modelling of the phase change inside the nodule coupled with a CFD simulation of the external flow to describe the mutual influence of the natural convection and the kinetics of crystallization. This study is afterwards extended to the case of two superposed nodules to investigate the influence of the crystallization of the lower nodule on the upper one.