Numerical simulation and optimization of phase change heat storage units using Slag-Based composite phase change materials

To address the significant waste of steel blast furnace slag (BFS) materials and waste heat resources, this study establishes numerical models for phase change heat storage bricks using composite phase change materials (CPCMs) developed by combining BFS with inorganic salts. Numerical simulations were conducted on the heat storage unit, and the results were validated against experimental data from literature and compared to those obtained from a pure BFS heat storage unit. Subsequently, an analysis was performed to investigate the influence of several key factors on the heat storage and release processes of the composite phase change heat storage units (CPCHSU), including inlet temperature, flow velocity, and different configurations of heat storage brick structures. The results indicate that within the temperature range of 25 °C to 340 °C, the PCHSU exhibits a heat storage capacity of 647.3 J, a heat storage rate of 0.49 W/kg, and a heat release rate of 0.65 W/kg, which are respectively higher than those of the pure BFS heat storage unit by 24.6 %, 22.5 %, and 61.5 %. Considering economic factors and practical application conditions, the optimal operating conditions were determined as follows: heat storage at Tin = 400 °C, heat release at Tin = 25 °C, and a flow velocity of 2.5 m/s. Based on these findings, simulations were conducted for different models under the optimal conditions revealing that the cross-shaped heat storage unit exhibited the highest recorded heat storage capacity of 706.6 J among all tested configurations. The research findings presented in this paper can provide essential theoretical references for the application of BFS based CPCMs.