Pioneering heat transfer enhancements in latent thermal energy storage: Passive and active strategies unveiled.

Intermittent renewable energy sources such as solar and wind necessitate energy storage methods like employing phase change materials (PCMs) for latent heat thermal energy storage (LHTES). However, the low thermal conductivity of PCMs limits their thermal response rate. This paper reviews recent progress in active heat transfer augmentation methods for improving LHTES system performance, encompassing mechanical aids, vibrations, jet impingement, injection, and external fields. It compiles findings concerning the optimization of PCM charging and discharging processes. Proposals for future research directions are provided, highlighting the significance of extra energy input for storage. The study highlights how changing the mushy zone constant from 10 to 10 affects a PCM's melt fraction and heat storage. The article also overviews studies using fins and coils to enhance heat transfer in PCM-based LHTES systems. It discusses how geometric and material constraints influence the melting and solidification processes and the heat transfer surface orientation within the storage tank. Various PCMs with different melting temperatures are examined. A broad range of test cases was examined to determine how geometry and orientation-dependent convection affect the phase-changing process. This overview of heat transfer principles offers guidelines for system designers to optimize the geometry of heat transfer fluid (HTF) flow paths and the confinement of PCM to enhance heat transfer efficiency and overall system performance. The results also indicate research gaps for certain PCM melting temperature ranges. Few experimental studies exist for melting temperatures above 60 °C; most focus only on melting rather than solidification. More standardized studies using non-dimensional parameters for coil geometries are advocated.