Numerical investigation on phase change materials (PCM): The melting process of erythritol in spheres under different thermal conditions

In this paper, a numerical study on the melting process of the PCM erythritol in 12 and 7 mm diameter spheres subjected to external flow has been carried out. This configuration is analyzed varying the temperature difference between the PCM melting point and the external flow, the Reynolds number as well as the sphere position in the array. The problem is considered two-dimensional in geometry and transient in time. The numerical model here developed consists of the continuity, momentum and energy equations. The results have been initially validated using numerical and experimental data from literature. Afterwards, results of liquid fraction, heat flux and total melting time have been proposed and illustrated. Based on pure observation, a slight difference in the phase change phenomena when comparing different sphere positions in the array has emerged. These phenomena proved to be much more influenced by the external flow temperature and by the Reynolds number. In all cases, at 30% of the total melting time, 50% of the total energy had been absorbed by the PCM. The liquid PCM layer above the solid has a great influence on the heat flux, precisely the more extensive the PCM layer, the lower the heat exchange. The local heat flux value decreases significantly in regions in contact with air and liquid PCM. Contrarily, at the sphere base, where there is solid PCM during the whole process, the local heat flux value is almost constant during the whole melting. Finally, significant differences have emerged when comparing the results referred to the hypothesis here contemplated of uniform heat transfer coefficient and local heat transfer coefficient function of the sphere angle.