Term of Award

Spring 2022

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Sevki Cesmeci, PhD

Committee Member 1

Prakashbhai Bhoi, PhD

Committee Member 2

Wayne Johnson, PhD

Abstract

Supercritical CO2 (sCO2) power cycles are superior to traditional water-based, air-breathing, direct-fired, open Brayton cycles; or indirect-fired, closed Rankine cycles in terms of efficiency and equipment footprint. They hold great potential in nuclear power production, fossil fuel power plants, concentrated solar power, geothermal power, and ship propulsion. To unlock the potential of sCO2 power cycles, technology readiness must be demonstrated on the scale of 10 – 600 MWe and at the sCO2 temperatures and pressures of 350 – 700 ºC and 15 – 30 MPa for nuclear industries. The lack of suitable shaft seals at sCO2 operating conditions is one of the main challenges at the component level. So far, conventional seals are incapable of handling sCO2 pressure and temperature in one way or another. This study proposes a patented novel Elasto-Hydrodynamic (EHD) high-pressure, high temperature, and scalable shaft seal for sCO2 turbomachinery that offers low leakage, minimal wear, low cost, and no stress concentration. The focus of this paper was to conduct a proof-of-concept study with the help of computer simulations. To this end, a fully coupled Fluid-Structure Interaction (FSI) modeling approach was adopted, and the simulations were carried out in COMSOL Multiphysics software. The modeling approach was presented thoroughly, the results were discussed, and the subsequent research steps were highlighted. Under the EHD mechanism: the higher the pressures are, the tighter the sealing becomes while sustaining a continuous sCO2 film. a 2" diameter shaft static test rig was designed at Georgia Southern University before the actual dynamic testing at Sandia National Laboratories for proof-of-concept purposes. For simplicity, the working fluid was chosen to be Nitrogen, and the tests were conducted at room temperature. The test rig consisted of a 16.5 MPA N2 tank, steel tubing with compression type fittings, and OMEGA – PX5500C0-2.5KA10E pressure sensor to measure the pressure of the N2 after the pressure regulator from the tank, a chamber housing the 2" steel shaft and EHD seal (two prototype steel seals with seal clearances of 25 μm and 50 μm), a CONAX – K-INC12-U-T3(5FT)-7.5" temperature sensor to collect temperature

data in the chamber, and an OMEGA – FMA-1623AI mass flow meter with temperature and pressure measurement capability to evaluate conditions after the test chamber. The pressure, temperature, and mass flow rate data were collected via a National Instruments DAQ – Module NI-9205 and a LabVIEW program. The tests were conducted for an inlet pressure of 0.1 ~ 15 MPa and at two different clearances of 25 μm and 50 μm. The mass flow rate exhibited a quadratic trend with increased pressure, which proved the hypothesis.

Research Data and Supplementary Material

No

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