The importance of the thermophysical characterization of microencapsulated PCMs for the numerical analysis of the heat transfer with solid-liquid phase change

Abstract

This work presents the development of two-dimensional numerical models based on the “additional heat source” and the “effective heat capacity” methods to simulate the thermal behaviour of a microencapsulated phase change material (PCM) - Micronal® DS 5001 X. A purely diffusive, transient model was used, where conduction is the only heat transfer mechanism during phase change. Different ways are evaluated to specify the variation of the equivalent heat capacity with temperature during the solid-liquid phase change: triangular and rectangular profiles, and also the experimentally measured specific heat as a function of temperature. The formulation of the triangular profile was based on previous studies of the authors, where a deficit of total stored/released energy was observed although predicting reasonably well the phenomena kinetics. This time, a new, consistent triangular profile method is used and its application can be generalized to different materials, by a single adjustment to the thermophysical characteristics of the PCM. This new formulation, designated as “triangular adjusted profile”, proved to be the most effective method, showing the best agreement with the previous experimental data obtained by the authors. The microencapsulated PCM is used to fill the rectangular cavities of an aluminium made thermal energy storage (TES) unit. Three different configurations of the TES unit were evaluated, in order to assess the influence of the number of aluminium fins in the PCM bulk. The melting/solidification time and the energy stored/released by the PCM were also evaluated for the different configurations. In general, the numerical results achieved are in good agreement with the experimental data previously obtained by the authors.