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

Cryogenic turboexpanders are widely utilized in hydrogen liquefaction systems and demand high-performance bearing technologies. A single-structured hybrid gas-magnetic bearing (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 turboexpander is substituted by a compressor impeller, allowing for the recycling of pressurized gas to the HGMB, thereby enhancing environmental pressure. The effects of environmental pressure on the static and the dynamic characteristics of the HGMB are investigated. A functional relationship between critical bearing number and pressure ratio 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 exceeds critical bearing number. Furthermore, the greater the relative value between actual bearing number and critical bearing number, 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 turboexpanders.