Thermal performance and design optimization for high-temperature (≥500 ℃) latent heat thermal energy storage device: Using modified steel slag/chlorides composite phase change materials

This work investigates the thermal performance of a novel high-temperature (≥500 °C) latent heat thermal energy storage (LHTES) device, using modified steel slag/chlorides composite phase change materials (C-PCMs) as heat storage medium. The research aims to enhance the energy storage capacity and thermal efficiency of steel slag-based C-PCMs in high-temperature applications. Numerical simulation based on a three-dimensional model was conducted to examine the influence of C-PCMs geometry and HTF parameters on thermal performance. The findings indicate that C-PCMs significantly outperform traditional steel slag-based sensible heat storage materials, achieving an 86 % increase in energy storage density, a 2.93-fold improvement in thermal conductivity, and a 2.76- to 9.46-fold increase in heat storage/release power. Importantly, key parameters and design rules were derived from inside heat transfer mechanisms to optimize device design. A new dimensionless parameter, heat restricted ratio (s’), was introduced to evaluate the melting performance of C-PCMs based on structural factors, providing insights for optimizing geometric structure. The results demonstrate that increasing the input power, especially higher inlet temperature, significantly accelerates the melting/charging process, although the benefits plateau due to heat conduction limitations within the C-PCMs. This research provides a critical foundation for optimizing structural and operational parameters of high-temperature LHTES device, thus advancing the application of the steel slag-based C-PCMs in thermal energy storage.