Numerical investigation of the influence of air layer on the melting behavior of RT42 PCM in a multi-hexagonal cell

To meet the growing need for sustainable energy solutions, improving the efficiency of thermal energy storage (TES) systems is important. In this study, the melting behavior of RT42 paraffin wax inside a hexagonal multi-cell was analyzed using numerical simulation based on the enthalpy-porosity method with ANSYS/FLUENT 16 software. The study focused on evaluating the effect of changing the thickness of the central air layer on the melting efficiency of the phase change material (PCM). Four cases were tested: one without an air layer and three others with thicknesses of 2 mm, 4 mm, and 6 mm. The results showed a clear quantitative relationship between the thickness of the air layer and the increase in melting time. The total time increased from 660 min (without air) to 780 min with a 2 mm thick air layer, an increase of 18%. The time reached 900 min at a thickness of 4 mm (37%) and 960 min at 6 mm (50%). These results show how important internal air layers are in reducing heat transfer efficiency, and how important it is to take them into account when designing phase change material-based thermal energy storage systems to get better performance and sustainability.