Enhancing double-tube thermal energy storage during solidification process: Effects of inner tube aspect ratio and its positioning

Given the growing scarcity of energy resources, energy storage has become increasingly important to researchers. In this context, numerical simulations are employed to assess the solidification process within a shell-and-tube thermal energy storage (TES) system. The TES system employs lauric acid as the phase change material (PCM), while water performs as the heat transfer fluid (HTF). The simulations take into account the influence of the aspect ratio (AR) in the range of 0.5 ≤ AR ≤ 1, and the non-dimensional location of the inner tube (Y) in the range of −0.2 ≤ Y ≤ 0.2. Initially, the numerical approach is verified qualitatively and quantitatively by using valid data existing in the literature. Subsequently, the findings cover the solid fraction (SF), temperature, average Nusselt number, and the solidification time along with temperature and SF contours. In conclusion, the results obtained emphasize the considerable influence of the geometry and positioning of the inner tube on the thermal performance of the TES system. Upon analysis of the system's temperature and SF distribution, it was found that the initiation of the conduction zone occurs earlier when the inner tube is twisted. Furthermore, placing the inner tube at Y = 0.2 leads to a reduction in the conduction zone of PCM at the upper part of TES. The most favorable scenario in terms of solidification time (SF) is observed with an AR of 0.5 and an inner tube positioning at Y = 0.2. The ST results showed that in the mentioned scenario took just under 400 min to finish the solidification process where this time was around 90 min less than the reference case (AR = 0 & Y = 0).