Performance enhancement of latent heat thermal energy storage by bubble-driven flow

In this study, the application of the bubble injection method to the phase change material (PCM) is proposed to improve charging performance of a latent heat thermal energy storage (LHTES). Due to the density difference between the PCM and the bubble, a bubble driven flow is generated by bubble injection into the LHTES and the mixing of liquid PCM is improved, which resulted in the mitigation of thermal stratification formation. Also, increased flow velocity enhances heat transfer between the heat source and PCM and can reduce LHTES charging time. To analyze the effect of bubble-driven flow, we compared and evaluated with and without bubble injection under the same flow conditions. As a result, in the 0.2, 0.4, and 0.6 L/min cases, the charging time decreased by 53, 40, and 37%, respectively, and the mean rate of energy storage increased by 218, 173, and 159%, respectively. To analyze the phase change pattern and the flow field of liquid PCM, the visualization techniques such as shadowgraphy and particle image velocimetry (PIV) were used. The injection of bubbles increased the mean velocity of liquid PCM by 638% and reduced the thermal stratification. The results clearly indicate that the bubble-driven flow could enhance the charging performance of the LHTES.