Comprehensive Numerical Modeling of Heat Pipe-Assisted Latent Heat Thermal Energy Storage Systems

Latent heat thermal energy storage (LHTES) is capable of higher energy storage densities effectively reducing storage volume and cost compared to other thermal energy storage systems. However, most inexpensive phase change materials (PCMs) exhibit low thermal conductivities, potentially limiting the rates of heat transfer, and consequently, the use of LHTES in a variety of applications. To compensate for this major drawback, three different approaches to improve heat transfer rates are presented in this work: (i) utilization of fins, (ii) incorporation of heat pipes (HPs), and (iii) use of combined HP/foils. These heat transfer enhancements are investigated both experimentally and numerically. The numerical model simulates the melting augmentation of a PCM housed within an internally-finned metal enclosure, followed by a derivation of analytical correlations. The experiments are conducted to generate and report data associated with the outward melting of a PCM induced by a heated rod under various tilt angles to investigate three dimensional effects. The benefits associated with exploiting HPs in LHTESs are also numerically investigated. A detailed and efficient numerical model is developed to simulate the conjugate and transient transport phenomena including vapor-liquid and meltingsolidification phase changes in the HP-PCM system. The numerical model is extended to consider different modes of operation including charging-only, simultaneous charging and discharging, and discharging-only. Finally, a combined HP-Foil-PCM system is investigated for further improvement of heat transfer rates experimentally as well as computationally. It was found that, in general, HPs exhibit higher heat transfer rates to/from the PCM compared to fins, especially when it is used in combination with foils (HP-Foil).