Thermohydrodynamic investigation for supercritical carbon dioxide high speed tilting pad bearings considering turbulence and real gas effect

A global heat balance method for supercritical carbon dioxide (S-CO2) high speed tilting pad bearings was developed, in which the real gas effect, variable thermodynamic properties, and turbulence effect were considered. The bearing characteristics can be obtained by the partial derivative method embracing dynamic variations of complete variables. Then thermohydrodynamic lubrication mechanisms for S-CO2 bearings are studied, and results indicate that the real gas effect of thermal compressibility is significant. The influence of the thermal effect on the static and dynamic characteristics of bearings is caused by changes in density, specific heat, and thermal expansion coefficient rather than viscosity, which is totally different from oil bearings. In general, the influence of thermohydrodynamic lubrication on static characteristics of S-CO2 tilting pad bearings is more obvious than that on dynamic coefficients. For example, the maximum deviation of damping coefficients of a bearing with parameters in this research at a certain speed range is 8%, and that of the load capacity at the corresponding speed is 10.7%. However, the influence of the thermal effect on dynamic coefficients is varied at different rotating speeds.