​Thermal storage systems are useful in a number of situations, from recovering waste heat from industrial processes and other surplus energy to increasing the production and use of thermal energy. Liten, a CEA Tech institute, which had previously developed an efficient and economically-affordable dual-media thermocline thermal energy storage technology for a CSP solar power plant, has now developed a unique tool for achieving the optimal mechanical dimensioning for this type of equipment.

Thermocline tanks, which use a combination of heat-transfer fluid and a solid matrix (granular materials like rocks, ceramic beads, post-industrial solid materials, etc.), are subject to a phenomenon called thermal ratcheting. In other words, when the tank heats up, it expands, and the granular material collapses to fill the gaps that form. When the tank cools, it contracts, and the compacted granular material exerts pressure on the tank. Liten developed a numerical model to investigate this little-studied phenomenon. The model—a cylindrical tank filled with spherical beads and subjected to heating/cooling cycles—integrates behavior rules for granular materials. At the same time, Liten also designed a test system made up of an aluminum tank filled with a combination of fluid and solid material to validate the model under thermal cycling.

These tools will be used to dimension tanks in a way that takes into account the pressure that builds up with each operating cycle. The tools will also be of use in any application—like grain silos and hydride storage tanks—where a solid matrix in a tank is subjected to expansion and contraction cycles.