Influence Mechanism of Environmental Pressure on Hybrid Gas-Magnetic Bearing Rotor System and Its Effective Enhancement Method

Cryogenic turbo-expanders are widely utilized in hydrogen liquefaction systems and demand high-performance bearing technologies. A single-structured hybrid gas-magnetic bearing (SS-HGMB) can satisfy these requirements and simplify the bearing structure; however, it compromises gas bearing (GB) performance due to increased radial clearance. In this work, the conventional fan brake of the hydrogen turbo-expander is substituted by a compressor impeller, allowing for the recycling of pressurized gas to the HGMB, thereby enhancing environmental pressure. The impacts of environmental pressure on the static and dynamic performances of the HGMB are investigated. A functional relationship between critical bearing number (Λc) and pressure ratio (ξ) is established, which serves as a criterion for assessing the impact of environmental pressure on HGMB performance. It is observed that bearing environmental pressure can significantly increase load capacity and reduce rotor vibrations when the actual bearing number (Λ) exceeds (Λc). Furthermore, the greater the relative value between Λ and Λc, the more effectively environmental pressure improves static and dynamic performances. These primary findings contribute to the design and performance enhancement of the GBs or HGMBs in turbo-expanders.