Performance Analysis of Salt-In-Pumice Composites Under Varying Air Velocities for Thermochemical Heat Storage

Thermochemical energy storage (TCES) offers significant potential for reducing reliance on fossil fuels while enhancing the utilization of renewable energy sources. The performance of TCES systems is critically influenced by the properties of thermochemical heat storage materials (TCMs), which directly affect both energy efficiency and storage capacity. In this study, a laboratory-scale experimental investigation was conducted to assess the performance of three pumice-based composite TCMs (P/LiCl-CaCl₂, P/CaCl₂, and CS-P/CaCl₂) under varying air velocities. Pumice particles with diameters of 1–3 mm were employed for P/LiCl-CaCl₂ and P/CaCl₂, whereas coarse size (CS) (4–6 mm) pumice was used for CS-P/CaCl₂. The primary objective was to evaluate the effects of particle size and LiCl incorporation on the thermal performance of composite TCMs. Key performance indicators, including energy efficiency (ηI), exergy efficiency (ηII), energy storage density (Ed), and outlet peak temperature (To,p), were determined. For P/LiCl-CaCl₂, average energy efficiencies of 64.0% and 76.6% were recorded at air velocities of 2.1 m/s and 3.7 m/s, respectively, with corresponding exergy efficiencies of 10.5% and 11.2%, and Tₒ,p values of 46.4 °C and 47.7 °C. The P/CaCl₂ composite achieved lower performance, with energy efficiencies of 44.7% and 48.4%, exergy efficiencies of 4.9% and 5.2%, and Tₒ,p values of 42.5 °C and 39.0 °C. For CS-P/CaCl₂, energy efficiencies were 64.2% and 72.2%, exergy efficiencies were 5.8% and 5.4%, and Tₒ,p values were 40.9 °C and 39.0 °C, respectively. The maximum Ed of approximately 181 kWh/m³ was observed for P/LiCl-CaCl₂ at 3.7 m/s. Across all composite materials, both energy efficiency and Ed increased with higher air velocity. Furthermore, the exergy efficiency of P/LiCl-CaCl₂ was nearly double that of the other two composites, indicating a clear advantage of LiCl incorporation combined with smaller pumice particle sizes.