Session: ASME Undergraduate Student Design Expo

Paper Number: 167196

A Novel Elastohydrodynamic Sealing for Sco₂ Turbomachinery 

Supercritical carbon dioxide (sCO₂) power cycles are emerging as a next-generation technology for various energy applications, including concentrated solar power, fossil fuel plants, geothermal electricity, nuclear power, and ship propulsion. For viability in the nuclear sector, sCO₂ turbomachinery must achieve technology readiness at scales of 10–600 MWe and operate under extreme conditions, with temperatures reaching 350–700 °C and pressures of 20–35 MPa. However, a significant challenge limiting efficiency and environmental sustainability in sCO₂ systems is the high leakage rate in existing turbomachinery seals, leading to performance losses and CO₂ emissions.

To address this issue, we propose a scalable elastohydrodynamic (EHD) shaft end seal designed for high-temperature, high-pressure sCO₂ turbomachinery. The seal employs elastohydrodynamic lubrication principles to minimize leakage and consists of a simple sleeve mounted on a back flange. Under non-operating conditions (Pin = Pout), the seal maintains an initial clearance of 25–50 µm. During operation (Pin >> Pout), pressure-driven flow through the clearance generates a decaying pressure distribution, causing the sleeve to form a restrictive throat near the fixed end, effectively reducing leakage. We hypothesize that a stable fluid film will persist in the clearance, preventing direct contact between the seal and the rotor, thereby minimizing wear.

To validate this concept, we conducted proof-of-concept experiments to assess the seal’s ability to restrict leakage under high-pressure conditions. Prior to dynamic testing at Sandia National Laboratories, a 2-inch static test rig was developed at Georgia Southern University for preliminary evaluation. Experiments were conducted at room temperature using nitrogen as the working fluid. The test setup included a CGA-580 N₂ tank, a cylindrical chamber housing the static shaft and seal, high-pressure steel tubing with compression fittings, pressure sensors (PX5500C0-2.5KA10E for inlet, PX409-1.0KA10V for outlet), a TC-K-1/4NPT-U-72 temperature sensor, and an FMA-1623AI mass flow meter. Data acquisition was performed using National Instruments DAQ modules (NI-9205, NI-9212, NI-9253) and LabVIEW software.

The test seal was fabricated from carbon graphite (elastic modulus: 21.4 GPa) and paired with a 2-inch diameter steel shaft. Initial tests were conducted with a 25.4 µm clearance, with intake pressures increased incrementally up to 8.00 MPa. The maximum recorded leakage rate was 4 g/s at 3.5 MPa, but as pressure increased to 7.5 MPa, leakage decreased to 0.5 g/s, forming a bell-shaped curve. At a 95% confidence level, the estimated confidence intervals for the mean leakage rates were ±0.12 g/s at 3.5 MPa and ±0.09 g/s at 7.5 MPa, confirming the throttling effect of the EHD seal.

Additionally, numerical simulations were performed using COMSOL Multiphysics, incorporating the High Mach Number Flow and Solid Mechanics modules. The simulation results closely aligned with experimental data, demonstrating the reliability of the model as a predictive design tool for EHD seals. This research establishes the feasibility of EHD sealing technology for sCO₂ turbomachinery, providing a scalable solution to mitigate leakage, enhance efficiency, and support the advancement of high-temperature, high-pressure power systems.

Presenting Author: Brenton Hall Georgia Southern University

Presenting Author Biography: Brenton Hall is a Sophomore in the Department of Mechanical Engineering at Georgia Southern University.

Authors:

Brenton Hall Georgia Southern University
Tyrus Carter Georgia Southern University
Tristan Graham Georgia Southern University
Sevki Cesmeci Georgia Southern University