Research papers Improving the charging performance of latent heat thermal energy storage systems using triply periodic minimal surface (TPMS) structures Mohamed G. Gado * Mechanical Power Engineering Department, Faculty of Engineering - Mataria, Helwan University, Cairo 11718, Egypt Istituto di Tecnologie Avanzate per l’Energia CNR ITAE, 98126, Messina, Italy ARTICLE INFO Keywords: Phase change material (PCM) Latent heat thermal energy storage (LHTES) Storage energy augmentation Triply periodic minimal surface (TPMS) ABSTRACT The utilization of latent heat thermal energy storage (LHTES) using phase change materials (PCM) has attracted considerable attention due to their high energy density and thermal regulation. However, the inferior thermal conductivity of PCM has hindered their widespread implementation, triply periodic minimal surface (TPMS) structures could considerably ameliorate the energy storage utilization. TPMS structures offer escalated surface area and pore interconnectivity, which can enhance the apparent thermal conductivity and improve the per- formance of LHTES systems. This study focuses on investigating the performance and storage capabilities of three unique TPMS structures, namely Gyroid, IWP, and Primitive, at different relative densities and charging tem- peratures. The computational model is developed, verified, and validated with the relevant experiment results. A comparative analysis of the temperature distribution and liquid fraction evolution in TPMS LHTES units is carried out and compared to pure PCM LHTES. At a charging temperature of 80 ◦ C, compared to the complete melting time of 7206 s for the pure PCM LHTES, the results demonstrate that the G10, IWP10, and P10-PCM LHTES achieve complete melting at 344 s, 276 s, and 368 s, respectively. This affirms the superiority of IWP structures in improving the melting rates due to their escalated surface areas and tortuous paths. The use of TPMS structures improves the total heat storage, heat storage rate, and volumetric heat storage density, while reducing the gravimetric heat storage density, compared to the pure PCM LHTES. The G10-PCM LHTES attains total heat storage, heat storage rate, volumetric, and gravimetric heat storage density of 2120 J, 6.16 W, 63.6 kWh/m 3 , and 227 kJ/kg, compared to 1910 J, 0.27 W, 57.3 kWh/m 3 , and 250 kJ/kg for pure PCM LHTES, respectively. Moreover, increasing the relative density of TPMS structures adversely reduces the total heat storage, heat storage rate, and volumetric heat storage density, and significantly increases the heat storage rates. As the charging temperature increases, the complete melting time is reduced and the charging performance indicators are improved, for the pure PCM and TPMS-PCM LHTES units. 1. Introduction The escalating energy demands and the severe deficit of energy re- sources advocate the utilization of renewable energy [1,2]. Neverthe- less, the instability and intermittent nature of renewable energy pose a noteworthy obstacle to its effective amalgamation within the current energy framework [3]. Latent heat thermal energy storage (LHTES) using phase change materials (PCM) is well-suited to addressing the limitations of renewable energy and has extensive applications in various domains. This is given their remarkable attributes, including high energy storage density, prolonged operational lifespan, and ability to promote environmental and energy conservation [1,4]. However, the prominent advantage of LHTES, its proliferation is still constrained by its inferior thermal conductivity which reduces energy utilization in terms of sluggish charging and discharging rates [5]. Consequently, extensive investigations have been dedicated to enhancing the latent heat utilization of PCM, primarily through the incorporation of extended heat transfer surfaces and thermal conduc- tivity enhancers. These strategies have included the use of conventional fins, fractal fins, shape memory fins, honeycombs, metal foams, Voronoi, and triply periodic minimal surface (TPMS) structures. The key features and performance characteristics of these various enhancement tech- niques are summarized in Table 1. To boost the heat transfer utilization of PCM, fins—as they can significantly boost the heat transfer rates within PCM-based * Corresponding author at: Mechanical Power Engineering Department, Faculty of Engineering - Mataria, Helwan University, P.O. 11718 Cairo, Egypt. E-mail address: gaber.m-gado@m-eng.helwan.edu.eg. Contents lists available at ScienceDirect Journal of Energy Storage journal homepage: www.elsevier.com/locate/est https://doi.org/10.1016/j.est.2024.114310 Received 14 February 2024; Received in revised form 24 August 2024; Accepted 18 October 2024 Journal of Energy Storage 103 (2024) 114310 Available online 25 October 2024 2352-152X/© 2024 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.