A scalable phase change material-based system enhanced by multi-walled carbon nanotubes and fins for efficient solar water heating applications

Phase change material (PCM)-based harvesting and storage systems are promising solutions to solar energy's intermittence and non-uniformity issues. Previous efforts have focused on the absorption, conversion, and storage capability of PCMs. However, efficiently utilizing the stored thermal energy within PCMs remains challenging. Herein, we devise a facile and scalable PCM-based system with heat transfer and light absorption enhancement simultaneously by fins and multi-walled carbon nanotubes (MWCNTs) for solar water heating applications. Photothermal conversion experiments demonstrate that the water temperature of the PCM-based system with MWCNT and fins is up to 79.0 degrees C under the stationary condition, which is increased by 58.6 % and 55.2 % compared to the original composite and the MWCNT-doped one, respectively. Furthermore, numerical simulations indicate that fins act as a bridge between PCM and water, facilitating rapid heat transport and improving the thermal energy storage pattern, enabling efficient solar water heating. The water temperature can keep above 40.0 degrees C for 51 min at a flow rate of 11.34 l/h under ambient cooling conditions, and the maximum thermal efficiency is up to 89.2 %, which is higher than most flat plate and tubular solar collectors, demonstrating the superiority of the proposed system.