Session: ASME Undergraduate Student Design Expo

Paper Number: 176173

A Novel Elastohydrodynamic Sealing for Sco₂ Power Cycles 

Supercritical carbon dioxide (sCO₂) power cycles are widely viewed as a leading pathway to higher efficiency and smaller footprints in next-generation energy systems, with clear relevance to small modular nuclear reactors. Yet the promise of these cycles is undercut by leakage in turbomachinery seals, which erodes thermodynamic efficiency and can increase CO₂ handling burdens. Addressing seal leakage is therefore essential to realizing the full benefits of sCO₂ technology.

We investigate an elastohydrodynamic (EHD) shaft-end seal as a practical, pressure-responsive solution. The EHD concept leverages fluid-structure interactions within a narrow clearance to develop a stabilizing hydrodynamic film and a self-adjusting restriction that throttles flow as pressure rises. To evaluate feasibility, we built a dedicated test rig featuring a 2-in stainless-steel static shaft and interchangeable seal specimens. Three materials, carbon graphite, virgin PEEK, and bearing-grade PEEK, were fabricated to identical geometries and tested across controlled conditions. Experiments were conducted at inlet pressures up to 13.5 MPa with initial clearances as tight as 0.001 in, covering 27 test configurations that sampled material, pressure, and clearance space.

Measured leakage demonstrated clear pressure-dependent throttling behavior characterized by bell-shaped mass-flow profiles across the operating range. Peak (highest observed) leakage rates were 3.96 g/s for carbon graphite, 3.60 g/s for virgin PEEK, and 8.15 g/s for bearing-grade PEEK. Notably, as the inlet pressure approached its maximum, leakage decreased substantially: to 0.33 g/s (carbon graphite), 0.96 g/s (virgin PEEK), and 3.37 g/s (bearing-grade PEEK). These trends are consistent with EHD expectations in which elastic deformation and evolving film dynamics reduce effective clearance and increase flow resistance under load. Differences among materials likely reflect contrasts in compliance, surface finish evolution, and thermo-mechanical response, all of which influence film formation and shear. Tests used dry, filtered CO₂ at ambient temperature; leakage measurements were repeatable within ±5%. Projected cycle analyses indicate potential 0.2–0.5 percentage-point efficiency gains for small modular reactor turbines under deployment.

Collectively, the results provide experimental proof-of-concept that the EHD seal can materially reduce sCO₂ leakage under high-pressure conditions. The observed throttling across all materials indicates robustness of the underlying mechanism, while the low end-of-range leakage values suggest a viable path to cycle-level efficiency gains. Ongoing work will expand to rotating tests, extended durability assessment, and coupled thermo-elastic analysis to optimize geometry and material pairing. Taken together, these findings position the EHD shaft-end seal as a promising candidate for integration into sCO₂ turbomachinery and a step toward unlocking the performance potential of advanced, compact power cycles.

Presenting Author: Lukas Marlow Georgia Southern University

Presenting Author Biography: Lukas Marlow is a senior in the Department of Mechanical Engineering at Georgia Southern University. He is currently a McNair Scholar conducting research under Dr. Sevki Cesmeci in his Thermofluidic Systems Laboratory.

Authors:

Lukas Marlow Georgia Southern University
Sevki Cesmeci Georgia Southern University