Novel Flexure Design for a High-Temperature Thermal Storage Vessel Coupled to a Free-Piston Stirling Engine

This paper presents the design and simulation of a novel flexure structure to potentially support a thermal energy storage (TES) salt vessel that is mounted on a solar dish Stirling Engine. During operation, the TES vessel expands significantly due to the elevated salt temperature leading to large deformation (thus high thermal stress) and large temperature change on the flexures. The flexure design consists of two sets of stacked flexures (∼100 mm in distance), each having eight stacked L-shaped flexures symmetrically distributed around the salt vessel. The axial and circumferential section of each flexure allows the radial and axial vessel expansion respectively. The stacking concept is expected to provide sufficient lateral rigidity (to avoid sag under gravity) while still allows the desired axial flexibility. Super Alloy Inconel 625 is selected as the flexure material due to its desired properties at elevated temperatures. A simplified model and a system model (including flexures, dummy engine, and salt vessel) of the design were analyzed using Finite Element Analysis (FEA). Analysis shows that the design meets the stress, deformation, and fatigues requirements. Test will be conducted to verify the simulation results. The flexure design is compact, simple, and low-cost to fabricate, and the concept can potentially be used for other applications that involve support of structures with large thermal expansion.