# Feasibility Analysis of Adopting the Hydrogen Hydrostatic Thrust Bearing
## 1 Introduction
Increasing spindle speed could lead to higher pressure on the spindle surface and increased spindle  
Figure 1: The application of gas bearings in a turbine system. (**a**) Turbine system schematic diagram. (**b**) Bearing system schematic diagram. stiffness [34]. [PERSON] et al. investigated the hydrodynamic hammering phenomenon and performance of a concave-hole single-tile bearing. The numerical calculation showed that the delayed effect of the pressure change in the gas chamber was a decisive factor for the pneumatic hammer phenomenon [35]. [PERSON] et al. analyzed features of pneumatic hammer self-excitation in hydrostatic bearings under different structural parameters and supplied pressures. It was found that because the flow rate and supplied pressure were larger than the corresponding critical values, gas hammer self-excitation tends to happen [36]. [PERSON] et al. conducted simulations of porous and partially porous hydrostatic thrust bearings to research the effect of disturbance frequency on dynamic characteristics. It was shown that the load capacity amplitude reduced as the frequency increased. Additionally, the damping of the partially porous bearing decreased with increasing orifice quantity [37]. [PERSON] et al. optimized the bearing design based on basic hydrodynamic equations for boosting performance [38]. [PERSON] et al. considered the influence of gas inertia force on the bearing and applied a CFD model for numerical verification and analysis [39]. [PERSON] et al. calculated gas bearings using air, carbon dioxide, hydrogen and helium as lubricating mediums using a CFD model. It was shown that the load capacity is significantly influenced by the lubricating medium. [40]. [PERSON] et al. investigated hydrostatic bearings lubricated using air, helium and hydrogen. Additionally, a model suitable for various lubricating media was proposed [41]. The above two studies, regarding the influence of lubricants, were founded on the laminar flow model; the influence of the flow states of lubricating mediums was not considered. At present, most research regarding turbo-expanders is conducted using air as the working medium [42; 43]. To improve bearing performance, the main structural parameters, such as the diameter of orifices, the location of orifices and the shape of gas chambers, are optimized [44; 45]. As the application of hydrogen bearings is not sufficiently mature, using small orifices to supply gas to hydrostatic thrust bearings when designing thrust bearings can provide more adequate load capacity and stable performance [46]. As a result of the special physical properties of hydrogen, design standards for HHTBs have not yet been defined. In practical applications, HHTBs are often used at high pressure around the bearing, and there is a large enthalpy difference during expansion. The increase in pressure around the bearing can cause the load capacity of the HHTB to be insufficient; if this occurs, the performance of the bearing is not completely adequate for high-speed operation, which can cause the hydrogen turbo-expander to fail during operation. With the purpose of investigating the feasibility of using the HHTB in this application, the performance of bearings using hydrogen was compared with the performances of bearings using other lubricating gases using the CFD turbulence model. Factors to improve the performance of HHTB were considered. The effects of supplied pressure, supply orifice diameter, the quantity of supply orifices, circumferential groove and gas film clearance on bearing performance were evaluated. The dynamic characteristics of HHTB under harmonic disturbance with various amplitudes, frequencies and gas film equilibrium values were studied.