Assessing the effect of size variation in graphite and alginate matrices for thermochemical heat storage

• Alginate-graphite-CaCl2 composites synthesised for heat storage applications. • Salt wt% decreases with increasing particle size. • Packing is improved but differential pressure is increased with decreasing bead size. • Smaller beads result in higher peak temperature and sustained temperature. • Varying charging temperature (90–150 °C) has minimal effect on charging efficiency. The charging and discharging performance of thermochemical heat storage (TCHS) materials within practical applications will be influenced by key material and reactor properties such as thermal conductivity, ease of airflow through the material bulk and moisture exchange kinetics. This study examines the impact of varying the bead size of Alginate-Graphite-CaCl 2 composites on the thermal and kinetic performance under static and dynamic conditions. Successful synthesis was achieved, with variations in composite composition ascribed to differential shrinkage factors during freezing. XCT studies highlighted improved packing with decreasing bead diameter although this significantly increases the differential pressure across the bed. Smaller diameters result in increased water sorption, which corresponds with higher peak temperatures and sustained temperature elevation during discharging analysis. Charging materials at temperatures between 90–150 °C has minimal effect on the ultimate charge profile. However, materials with large diameters display an improved charging efficiency advantage up to a charging level of 50 % but ultimately the smallest composites exhibit a slight efficiency improvement at 95 % charge.