• Energy Research

The design of thermal energy storage (TES) tank is the key part that can limit charging and discharging process. Most research findings highlight that the use of fins augments the heat transfer rate. This work experimentally investigates the use of aligned copper wools as fillers to enhance the thermal performance of a lab-scale shelland- tube TES tank filled with phase change material (PCM). Two copper wools with different fibre thicknesses were chosen and discretely laid around the TES tank tubes in two design patterns. Accordingly, five shell-andtube TES tank configurations were obtained, including the reference, for performance evaluation. The TES tank was loaded with n-octadecane as PCM for all the cases studied. The results showed up to a 16 % reduction in melting time with the inclusion of copper wool. The TES tank significantly increased the mean power during charging (53 %) and discharging (205 %). The addition of metal wool into the TES tank enables the PCM to release the heat at a constant temperature during the entire phase transition process. And the overall efficiency of the TES tank was found to get improved. Therefore, a copper wool integrated TES tank would be a beneficial addition to thermal energy storage systems. This project was funded by the European Union's Horizon Europe Research and Innovation Programme under grant agreement 101084182 (HYBRIDplus). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor the granting authority can be held responsible for them. This work was partially funded by the Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (AEI) (PID2021-123511OB-C31- MCIN/AEI/10.13039/501100011033/FEDER, UE and RED2022-134219-T). This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Department de Recerca i Universitats of the Catalan Government for the quality accreditation given to their research group (2021 SGR 01615). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia.

The adoption of thermal energy storage (TES) systems based on phase change material (PCM) remains limited by their low thermal conductivity, which restricts power density. Existing heat transfer enhancement techniques are often costly or come with significant drawbacks, leaving a gap for an effective and affordable solution. This study highlights metal wool as a promising alternative, offering low cost, ease of application, and retrofitting potential. While previous experiments demonstrated substantial improvements in power density using copper wool, a comprehensive numerical model to further optimize this technique is presented here. The model, incorporating CFD simulations and uncertainty analysis, was validated for bulk PCM and two copper wool-PCM composites before being extended to a wool material analysis. First, possible alternatives to copper as wool material were tested, highlighting aluminum as a viable candidate. Then, the proposed composite was found to match the discharging performance of a PCM with an effective thermal conductivity of 2.5 W/mK, a value rarely achieved by conventional enhancement techniques. Additionally, a techno-economic comparison revealed that copper wool delivered a 14.7-fold increase in thermal conductivity relative to liquid PCM at ¿6 per kg of PCM additivated¿a performance unmet by metal foams and nanocomposites. These findings confirm metal wool as a viable cost-effective and high-performance solution for improving TES systems, partially bridging the gap between efficiency and affordability. A.R. and E.C. acknowledge funding under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3—Call for tender No. 1561 of 11.10.2022 of Ministero dell’Università e della Ricerca (MUR); funded by the European Union—NextGenerationEU. This work was partially funded by the Ministerio de Ciencia e Innovacion’ - Agencia Estatal de Investigacion’ (AEI) (PID2021-123511OB-C31-MCIN/AEI/10.13039/501100011033/ FEDER, UE and RED2022-134219-T). This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Department de Recerca i Universitats of the Catalan Government for the quality accreditation given to their research group (2021 SGR 01615). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This paper is part of the RYC2023-044196-I, funded by MCIU/AEI/ 10.13039/501100011033 and FSE+. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101036910