Thermal Energy Transfer to a High-Temperature Working Substance as a Function of its Structure in a Thermal Energy Storage

Thermal energy storage represents a promising field for significantly enhancing the efficiency of renewable energy-based systems. This study proposes a thermal energy storage system utilizing a high-temperature working fluid composed of finely dispersed graphite particles. The aim of the work is to investigate the transfer of thermal energy to the high-temperature working fluid depending on its structural configuration. Nonlinear dependencies of graphite's thermal parameters are presented, which enhance the accuracy of numerical modeling. The numerical study reveals the dependence of thermal conductivity on the working fluid temperature under varying graphite particle configurations. The maximum thermal conductivity value (up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.71 \mathrm{W} /(\mathrm{m} \cdot{ }^{\circ} \mathrm{C})$</tex>) was observed when heat flux was applied from the square-shaped elements, a result attributed to the shortened heat transfer path. Additionally, chaotic particle distribution was found to enhance thermal conductivity through dense interparticle contacts and intensified radiative exchange, compensating for geometric irregularity.