Experimental verification of an elastohydrodynamic seal design for nuclear sCO₂power generation

Supercritical carbon dioxide (sCO₂) power cycles are poised to become a promising technology in the energy generation sector, particularly for small modular nuclear reactors. However, current turbomachinery utilizing sCO₂ faces significant challenges due to high leakage rates, which hinder the full potential of this power generation method. These elevated leakage rates not only penalize system efficiencies but also raise environmental issues by increasing CO₂ emissions into the atmosphere. To address these challenges, we propose an elastohydrodynamic (EHD) shaft-end seal as a potential solution. This study presents experimental proof-of-concept data supporting our proposed seal design's effectiveness in minimizing leakage under high-pressure conditions. We constructed a test rig featuring a 2-inch stainless steel static shaft and employed three different seals made from carbon graphite, virgin PEEK, and bearing-grade PEEK materials for evaluation. The experiments were run with inlet pressures reaching up to 13.5 MPa and with initial clearances as narrow as 0.001 inches, encompassing a total of 39 tests conducted across various configurations. The highest recorded leakage rates observed were 4.0 g/s for carbon graphite, 3.6 g/s for virgin PEEK seals, and 8.2 g/s for bearing-grade PEEK; however, these values decreased significantly, dropping to 0.3 g/s, 1.0 g/s, and 3.4 g/s respectively, as pressure rose to its maximum level. All tested seals exhibited throttling behavior characterized by bell-shaped mass flow rate profiles throughout their operation range. These findings indicate that the EHD seal could have a potential application within sCO₂ turbomachinery systems.