Experimental study on the influence of geometry for convection enhancement in bubble-driven latent heat thermal storage system

This study investigates a bubble-driven system on the heat transfer performance of eicosane-based rectangular LHTES (Latent Heat Thermal Energy Storage), and evaluates its scalability in height and width. Temperature and visualization experiments were conducted to examine thermal behavior and phase change characteristics. When bubbles are injected, rising bubbles entrain surrounding liquid PCM, generating vigorous upward flows and agitation with the return downward flow completing circulation loop. This promotes convective heat transfer, resulting in more uniform melting in vertical direction and effectively mitigating thermal stratification. Consequently, bubbles accelerate melting and enhance energy absorption rate compared to non-bubble-driven case. Varying the system height showed consistent flow pattern and heat transfer performance. An increase in system lateral width limits downward flow near the heating surface, resulting in delayed melting and reduced overall efficiency. In addition, dimensionless correlations of liquid fraction were proposed for both bubble-driven and non-bubble-driven cases, providing applicability for the design and prediction of rectangular LHTES with various configurations. The energy analysis showed that the ratio of the mass-based heat absorption rate increased by up to 58.53% with the bubble-driven system at higher heights. Meanwhile, the improvement was only 17.86% for the 90 mm width case due to limited flow circulation near the heating surface. The energy required for bubble injection accounted for less than 0.35% of the absorbed energy in PCM, confirming the efficiency and cost-effectiveness of this enhancement method.