# Feasibility Analysis of Adopting the Hydrogen Hydrostatic Thrust Bearing
## 3 Influence of Lubricant Properties  
Bearing performance is profoundly influenced by the applied gas lubricant. Numerical calculations and comparisons of the static performance of bearings using hydrogen and other common gases have been carried out for a comprehensive understanding of the performance characteristics of HHTBs. Commonly used gaseous lubricants that have similar physical properties, such as low density and viscosity, can be analyzed according to an identical calculation model. However, in engineering applications, bearings are affected by differences in gaseous physical properties. The density and viscosity of hydrogen are lower compared to those of air, methane and helium, as indicated in Table 2. With a view to investigating the performance characteristics of HHTBs, the above-mentioned lubricating gases were selected for calculation and comparison. The parameters applied in the calculations are presented in Table 3. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Structural Parameters** & **Value** & **Unit** \\ \hline Bearing internal diameter (\(D_{1}\)) & 25 & mm \\ Bearing external diameter (\(D_{2}\)) & 80 & mm \\ Radius of the orifice circle (\(R_{d}\)) & 25 & mm \\ Orifice diameter (\(d\)) & 0.2 & mm \\ Number of orifices (\(N\)) & 6 & / \\ Groove depth (\(h\)) & 0 & mm \\ Groove width (\(s\)) & 0 & mm \\ Pressure around the bearing (\(P_{0}\)) & 101,300 & Pa \\ Supplied pressure (\(P_{in}\)) & 607,800 & Pa \\ Temperature (\(T\)) & 293 & K \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Bearing parameters from the literature [51] used for validation. Figure 4: Model verification: (**a**) grid independence verification and (**b**) load capacity validation. The static parameters of bearings using different gases are presented in Figure 5. The load capacity of the HHTB was less than that of helium-lubricated bearings but higher than that of air- and methane-lubricated bearings. As film clearance increased, load capacity decreased. Furthermore, the peak static stiffness values of bearings using air and methane were similar and higher than those using helium and hydrogen. Film clearances that corresponded to the peak values for air and methane were smaller than those for helium and hydrogen. With an increment in film clearance, the static stiffness initially increased, then decreased. In general, the HHTB had a significant load capacity, although its stiffness was relatively smaller. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Gas** & **Density (kg\(\cdot\)m\({}^{-3}\))** & **Viscosity (\(\upmu\)s)** \\ \hline Air & 5.8149 & 18.595 \\ Methane & 3.2432 & 11.189 \\ Helium & 0.8004 & 19.944 \\ Hydrogen & 0.4029 & 8.9407 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Density and viscosity of hydrogen, air, methane and helium at 300 K, 0.5 MPa. Figure 5: Static parameters of bearings using different gases: (**a**) load capacity and (**b**) static stiffness. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Structural Parameters** & **Value** & **Unit** \\ \hline Bearing internal diameter (\(D_{1}\)) & 25 & mm \\ Bearing external diameter (\(D_{2}\)) & 50 & mm \\ Radius of the orifice circle (\(R_{d}\)) & 19 & mm \\ Orifice diameter (\(d\)) & 0.2 & mm \\ Number of oritices (\(N\)) & 8 & / \\ Groove depth (\(h\)) & 0.2 & mm \\ Groove width (\(s\)) & 0.2 & mm \\ Film clearance (\(c_{0}\)) & 10 & \(\upmu\)m \\ Pressure around the bearing (\(P_{0}\)) & 500,000 & Pa \\ Supplied pressure (\(P_{in}\)) & 1,000,000 & Pa \\ Temperature (\(T\)) & 293 & K \\ Rotational speed (\(\omega\)) & 50,000 & rpm \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Structural and operational parameters of thrust bearings. When the bearing diameters are determined, the load capacity increases as the restrictor coefficient.