Topology optimization of phase-change energy walls considering boundary conditions and thermal interference effects

Abstract

This study proposes a topology-optimized phase-change energy wall (TPEW) enhanced with PCM-enhanced concrete (PEC) and develops a coupled three-dimensional thermo-hydro-mechanical finite element model to systematically analyze the heat exchange performance and thermo-mechanical coupling characteristics of TPEWs under various optimization strategies and boundary conditions. Results show that TP-G and TP-T distinctly affect PEC zones depending on pipe configurations: for DW 1U-pipe, TP-G shifts PEC toward the soil, while TP-T shifts it toward the pipe; for DW 2U-pipe, TP-G forms X-shaped PEC, while TP-T forms droplet-shaped PEC near the pipes; for PW 1U-pipe, TP-G distributes PEC horizontally, while TP-T distributes it vertically; for PW 3U-pipe, TP-G forms I-shaped PEC, while TP-T creates six isolated zones. Under seepage, TP-T shifts PEC downstream as seepage velocity v_w increases, whereas under airflow, TP-T shifts PEC toward the soil-side as airflow velocity v_a increases. Temperature-dominated topology (TP-T) enhances heat exchange power, gradient-dominated topology (TP-G) reduces thermal stress and thermal interference TP-T further improves power. Compared with conventional center-backfilled (CB), the maximum power increases of TP-T under pure soil, seepage, and air boundary conditions are 25.7%, 6.2% and 20.5%, respectively. Under pure soil, seepage, and air boundary conditions, TP-TI further enhances power for larger pipe configurations, achieving increases over TP-T of 12.6%, 19.5%, and 5.4%, and reduces heated zones by up to 22%. In summary, the topology-optimized PEC zones effectively enhance power, reduce thermal stress and long-term stability, providing practical guidance for the design and optimization of phase-change energy walls under various pipe configurations and boundary conditions.