An Advanced Gas Foil Bearing Using Supercritical Carbon Dioxide as the Working Fluid

As new applications arise for supercritical CO2 (sCO2) power generation, and higher efficiencies are achieved through higher system pressures and temperatures, the need to improve technologies becomes essential. Traditionally lubricated and cooled oil bearings cannot tolerate these temperatures, and the higher pressures makes keeping the oil separate from the sCO2 an increasingly difficult challenge. These conditions strongly promote using the sCO2 as the lubricant, rather than oil. This grant application seeks to develop a new gas foil bearing that meets these needs by using the sCO2 as the lubricating fluid by substantially advancing the art to provide increased load capacity, damping, and wear resistance. To achieve project objectives, best in class technologies in pressurized hydrostatic gas bearings and hydrodynamic gas foil bearings will be combined to produce an advanced hydrostatically assisted hydrodynamic gas bearing design. Analytical models and codes were updated to include the fluid properties of sCO2. Novel bump foil geometries and patterns were evaluated to maximize stiffness and damping characteristics. Candidate coatings were evaluated for start stop wear resistance. Prototype bearings were fabricated and installed in a high speed test rig for validation testing (using air) of hydrostatic and hydrodynamic performance. Refinement of the analytical models will continue in order to predict bearing performance using sCO2 as the working fluid. Design data will be obtained from sCO2 machinery OEMs (including a major OEM collaborator) as a basis for generating full scale bearing designs. Foil and hydrostatic pocket geometries will be optimized for the larger bearings. Prototypes will be designed, fabricated, and validation tested in a representative sCO2 environment. The proposed effort directly supports both commercial and federal interests. Foil bearings are an enabling technology which allows the creation of machines that otherwise could not be built, particularly in high speed machines or in ultrapure systems like sCO2 where contaminants, such as oil or grease, cannot be tolerated. Advancements in the technology can be immediately utilized in a variety of applications ranging from sCO2 systems, ground based gas turbine powered electric power generators, compressors, refrigeration equipment, vehicular systems (turbochargers, fuel cell blowers), aerospace environmental control systems, auxiliary power units, small to medium propulsion gas turbines, and rocket turbo pumps. Key Words: Supercritical CO2, gas foil bearings, oil free bearings, hydrodynamic bearings, hydrostatic bearings, turbo expander, compressor, high temperature bearings, high pressure bearings. This project will develop an advanced foil bearing using high pressure/ temperature sCO2 as the lubricating fluid. This will enable the development of more efficient power generation equipment, resulting in energy savings with its reduction in fossil fuel consumption and associated Greenhouse Gas emissions, and will produce jobs in the U.S. bearing industry.