Latent heat thermal energy storage (LHTES) systems are designed to store excess thermal energy, addressing supply-demand mismatches during periods of low supply. Integrating such systems in the field is challenging due to the slow charging caused by the low thermal conductivity of phase change materials (PCM). This shortfall can be mitigated using composite PCM (CPCM) as the thermal storage medium, consisting of form-stable porous graphite foam impregnated with PCM. Compressed expanded graphite (CEG) is one such easily accessible form-stable porous material. The graphite foam in the CPCM causes a significant improvement in the effective thermal conductivity of the storage medium; however, it causes reduced latent heat storage capacity. Existing literature on CPCM mainly emphasizes positive aspects like enhanced thermal conductivity and reduced melting time while overlooking the adverse impact on latent heat storage capacity. This trade-off must be addressed while designing such a system, particularly when the storage unit is of fixed size and shape. This study aims to find the optimal volumetric proportion of CEG in CPCM, striking the best balance between these two conflicting attributes. Objective parameters such as energy storage ratio (ESR) and capacity ratio (CR) are introduced, along with charging duration, and they are optimized based on control parameters like CEG foam porosity (ε), HTF inlet temperature (Tin), and flow Reynolds number (Re). The analysis, obtained from a volume-averaged numerical model, involves diffusion-dominated energy transfer in the CPCM domain and provides crucial design guidelines for fixed-geometry LHTES units with CPCM as the storage medium.

中文翻译：

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优化石墨增强复合相变材料，在管壳式潜热存储系统中实现卓越的热传输


潜热热能储存 （LHTES） 系统旨在储存多余的热能，解决低供应期间的供需错配问题。由于相变材料 （PCM） 的低导热性会导致充电缓慢，因此在现场集成此类系统具有挑战性。使用复合相变材料 （CPCM） 作为蓄热介质可以缓解这种短缺，该介质由浸渍相变材料的形状稳定的多孔石墨泡沫组成。压缩膨胀石墨 （CEG） 就是这样一种易于获得的形状稳定的多孔材料。CPCM 中的石墨泡沫导致存储介质的有效导热性显着提高;但是，它会导致潜热存储容量降低。关于 CPCM 的现有文献主要强调积极的方面，例如增强导热性和减少熔化时间，而忽略了对潜热存储容量的不利影响。在设计此类系统时，必须解决这种权衡问题，尤其是当存储单元具有固定大小和形状时。本研究旨在找到 CPCM 中 CEG 的最佳体积比例，在这两个相互冲突的属性之间取得最佳平衡。介绍了储能率 （ESR） 和容量率 （CR） 等目标参数以及充电持续时间，并根据 CEG 泡沫孔隙率 （ε）、HTF 入口温度 （Tin） 和流动雷诺数 （Re） 等控制参数对其进行优化。该分析来自体积平均数值模型，涉及 CPCM 域中以扩散为主的能量转移，并为以 CPCM 为存储介质的固定几何 LHTES 单元提供了重要的设计指南。