Computational Model Development for Hybrid Tilting Pad Journal Bearings Lubricated with Supercritical Carbon Dioxide

Featured Application Power generation systems based on supercritical carbon dioxide. Fluid film bearings lubricated with supercritical carbon dioxide (sCO(2)) eliminate the infrastructural requirement for oil lubricant supply and sealing in turbomachinery for sCO(2) power systems. However, sCO(2)'s thermohydrodynamic properties, which depend on pressure and temperature, pose a challenge, particularly with computational model development for such bearings. This study develops a computational model for analyzing sCO(2)-lubricated tilting pad journal bearings (TPJBs) with external pressurization. Treating sCO(2) as a real gas, the Reynolds equation for compressible turbulent flows solves the pressure distribution using the finite element method, and the Newton-Raphson method determines the static equilibrium position by simultaneously calculating forces, moments, flow rates of externally pressurized sCO(2), and pressure drop due to flow inertia. The finite difference method solves the energy equation for temperature distribution. The density and viscosity of sCO(2) are converged using the successive substitution method. The obtained predictions agree with the previous and authors' computational fluid dynamics predictions, thus validating the developed model. Hybrid lubrication increases the minimum film thickness and stiffness up to 80% and 65%, respectively, and decreases the eccentricity ratio by up to 65% compared to those of pure hydrodynamic TPJB, indicating significant improvement in the load capacity. The bearing performance is further improved with increasing sCO(2) supply pressure.

Automated summary

This study develops a computational model for analyzing tilting pad journal bearings lubricated with supercritical carbon dioxide (sCO(2)). The model successfully predicts the pressure distribution, static equilibrium position, and temperature distribution of the bearings using numerical methods such as the Reynolds equation, Newton-Raphson method, and finite difference method. The results show that hybrid lubrication significantly improves the load capacity of the bearings, and increasing the supply pressure of sCO(2) further enhances the bearing performance.