Latent heat thermal energy storage: Theory and practice in performance enhancement based on heat pipes

Latent heat thermal energy storage is an important component in the field of energy storage, capable of addressing the mismatch of thermal energy supply and demand in time and space, as well as intermittent and fluctuating issues. The low thermal conductivity of phase change materials (PCMs) limits their large-scale application in the field of thermal storage. The coupling of heat pipes (HPs) with PCMs is an effective method to enhance latent heat thermal energy storage. This paper summarizes five typical coupling methods between the two: PCM is placed in the evaporation section, condensating section, or adiabatic section of the HP, or the HP is entirely embedded in the PCM as a thermal conductive framework. The research progress on HP-enhanced latent heat storage systems is summarized from three aspects: HP and PCM coupling applications, HP heat transfer models, and simulation studies. However, existing studies mainly design coupling systems from a structural perspective, without considering the matching relationship of the inherent thermal storage/transfer capabilities of PCMs. Future research needs to clarify the contribution ratio of PCM and HP to heat transport in the overall thermal control process, and also expand multi-scale and multi-physical field simulation studies. Establishing the correlations among microscopic molecular phase changes, mesoscopic transport behaviors, and macroscopic thermal control performance, capturing information that is difficult to obtain experimentally to explore dominant limiting factors. To enhance the adaptability of HP-based thermal storage systems to dynamic conditions and broaden their application range.