Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 146127

146127 - An Elastohydrodynamic High-Pressure Seal for Super Critical Carbon Dioxide Power Plants 

Supercritical carbon dioxide (sCO₂) power cycle is a next-generation power technology with a promising potential to be used in concentrated solar power, fossil fuel power plants, geothermal electricity, nuclear power, and ship propulsion. The technology readiness must be demonstrated on a scale of 10–600 MWe and at temperatures and pressures of 350–700 °C and 20–35 MPa, respectively, for nuclear industries. Current sCO₂ turbomachinery suffers from high leakage rates, which is creating a major roadblock to the full realization of sCO₂ power technology. The high leakage rates not only penalize the efficiencies but also create environmental concerns due to greenhouse effects caused by increased CO₂ discharge to the atmosphere. As a potential solution, we propose an elastohydrodynamic (EHD) scalable, high-temperature, high-pressure shaft end seal for sCO₂ turbomachinery. The EHD seal leverages the proven elastohydrodynamic lubrication theory. The seal itself consists of a very simple design, i.e., a sleeve attached to a back flange. In non-operating conditions, i.e., P_in=P_out, the seal is seated on a rotor with an initial clearance of 25-50 μm. During operation, P_in>>P_out, there is flow through the clearance, creating a decaying pressure distribution in the clearance. While this is happening, the pressure at the top of the sleeve structure is constant and is equal to the inlet pressure. Because the sleeve’s one end is free, and the other end is attached to the flange as well as the constant and decaying pressure distribution at the top and bottom of the sleeve, respectively, the seal forms a throat closer to the fixed end to act as a flow restrictor. This is a similar phenomenon as in the case of a throttling valve. The main difference is that the EHD seal throttling is occurring dynamically. The EHD seals have promising potential in various engineering applications, including oil and gas and power industries. In this study, an experimental approach has been presented for proof-of-concept purposes. A test-rig was fabricated for 2-in stainless steel shaft. The test seal was made of Ketron ® HPV PEEK, bearing grade. The trials were run with an inlet pressure of up to 15 MPa and an initial clearance of 31.44 μm. The maximum leakage rate recorded was 8.16 g/s at 5 MPa. Following then, the leakage rate began to drop down to 2.24 g/s as the pressure increased to 15 MPa, generating a bell-shaped curve. At a 95% confidence level, the estimated confidence intervals for the mean were ±0.18 g/s and ±0.05 g/s for pressures of 5 MPa and 15 MPa, respectively. These preliminary findings suggest that the proposed EHD seal design can potentially be applied to sCO2 turbomachinery.

Presenting Author: Jonah Henry Georgia Southern University

Presenting Author Biography: Mr. Jonah Henry is a senior and an Undergraduate Research Assistant in the Department of Mechanical Engineering at Georgia Southern University. Jonah has been researching innovative elastohydrodynamic seals for the past three years under the supervision of Dr. Sevki Cesmeci at the Thermo Fluidic Systems Laboratory. This research has been funded by the Department of Energy through STTR Phase I and II grants.

Authors:

Jonah Henry Georgia Southern University
Sevki Cesmeci Georgia Southern University