Investigation of heat transfer characteristics in steel fiber-reinforced energy piles utilizing steel tubes for PCM encapsulation

Changqing Xia, Guancong Chen, Jiaxing Shi, Xiaohua Bao and Hongzhi Cui

Energy, 2025, vol. 326, issue C

Abstract: Phase change materials (PCMs) significantly enhance the heat transfer performance of energy piles, with the choice of encapsulation form being crucial to maximizing their potential. This study proposes a novel energy pile encapsulated with PCM in steel tubes (TuPCM pile) and assesses its heat transfer performance (HTP) through laboratory tests. A comprehensive analysis examines how PCM encapsulation, inlet temperatures, flow rates, operation modes, and flow cycles affect the heat transfer characteristics of energy piles. A 3-D numerical model was developed to investigate the heat transfer mechanisms of energy piles. The results show that under cooling conditions, energy piles with steel tube-encapsulated PCM outperform those with PCM steel balls and ordinary ones, with HTP improvements of 16.3 % and 35.7 %, respectively. The HTP of the TuPCM pile increases with the flow rate, showing a 317.1 % improvement at 0.25 m3/h compared to the ordinary pile. The performance of energy piles is proportional to the temperature variation between the circulating fluid and the initial soil temperature. A temperature variation of 20 °C results in a 40.24 % improvement in TuPCM piles over ordinary ones. The 6 h on-18 h off mode enables energy piles to reach optimal performance, showing an 87.13 % improvement over the ordinary one. In multi-cycle modes, the performance of the TuPCM pile decreases by 22.97 % by the tenth cycle, while the performance of the ordinary pile sees a more pronounced decline of 32.82 %. Numerical simulations reveal that PCM energy piles exhibit a greater temperature gradient with the soil, enhancing heat transfer.

Keywords: PCM energy pile; Steel tube encapsulation; Heat transfer characteristics; Model test; Numerical analysis (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:326:y:2025:i:c:s0360544225019152

DOI: 10.1016/j.energy.2025.136273

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