Experimental determination of crystallization kinetic model of CENG-PCM composite material. Validation at macro and meso scales

Abstract

• Two different crystallization mechanisms are observed in the PCM. • A visualization experiment is performed for morphological identification. • Crystallisation kinetic modelling is carried out by using Nakamura kinetics models. • The crystallisation kinetic model is validated at micro and macro scales. This article presents a method for modelling the crystallisation kinetic of a phase change composite material when two transformations occur during the solidification. To obtain the full description of the crystallization process, the DSC analysis was completed with visualisations and extrapolations based on physical and analytical assumptions. This method has been validated successfully at different scales with paraffin and with paraffin embedded in Compressed Expanded Natural Graphite (CENG) matrix. The phase change material studied was a paraffin RT70HC from Rubitherm®. The validation experimental cases were performed on a plate of CENG-RT70HC composite cooled from its side and a packed-bed heat storage exchanger with a filler composed with encapsulated CENG-RT70HC capsules. The kinetic model was implemented in the finite element code Comsol® adding a source term to the energy equation. This model simulated closely the temperature evolution of a phase change material during a cooling. We found that the crystallisation kinetic is the same for the paraffin and for the paraffin with CENG showing that the CENG do not apparently affect the kinetic crystallisation of the paraffin.