# Thermal Characteristics Study of the Bump Foil Thrust Gas Bearing
## 3 Thermal Analysis
### Analysis of Influence Factors of Bearing Temperature
When the initial minimum gas film thickness is the same, the bearing load capacity and friction loss power both increased when the rotor speed goes up, and the difference between the values of the bearing load capacity calculated by the THD model and the isothermal model increased significantly when the speed reach to higher value. This is due to the rapid rise of the gas film temperature caused by the increased rotational speed, and the gas viscosity increases with the temperature rising up. Figure 10: Static characteristics under different thermal model. (**a**) Load capacity; (**b**) Friction loss power. Figure 9: Dimensionless gas film pressure distribution under different thermal model. (**a**) Isothermal model; (**b**) THD model. Figure 11 is the temperature distribution diagram of top foil under the rotor speed of 50 krpm and the static load of 100 N. Similar with the distribution of gas film pressure, the surface temperature of the top foil experiences, firstly, increasing along the rotor rotating direction and then maintaining at a certain value. In the entrance area, the temperature of the ambient gas that is brought into the gas film is relatively low, and it will rise sharply after mixing with the recirculation hot air. The top foil temperature in the plane section is almost the same, which is obviously higher than that in the inclined region. In the radial direction, the temperature increases first and then decreases slightly as the radius increases. This is because the larger radius indicates the larger linear velocity of the gas film and the larger amount of heat generated due to viscous friction. The decreasing trend near the edge can be explained as the heat is dissipated by the forced convection on the thrust plate outer radius surface. Figure 12 shows the relationship between bearing temperature and the static load at the rotor speed of 50 krpm. The temperatures of top foil and thrust plate are the average values in the simulations. It can be seen from the figure that as the bearing load increases, the gas film temperature increases almost linearly. Additionally, when the bearing load increases, the differences between the maximum air film temperature, the top foil temperature and the thrust plate temperature are almost kept constant. The increase in bearing static load means the gas film is compressed, and the heat generated by the viscous dissipation and the compression in the gas film is larger, resulting in the rise of overall temperature. Figure 11: Top foil temperature distribution. Figure 12: Relationship between bearing temperature and load. Figure 13 shows the variation of bearing temperature influenced by rotor speed under the bearing static load of 100 N. As the bearing speed increases, the temperatures of gas film, top foil, and thrust plate all increase exponentially. Therefore, rotor speed has a greater influence on the bearing temperature compared with the influence of static load. At low rotor speeds, the difference between the top foil and the thrust plate average temperatures is relatively small, and the maximum temperature of gas film is also relatively small. As the rotational speed increases, the differences between the temperatures of the top foil, thrust plate, and the maximum gas film temperature also increase. Figure 14 shows the temperature distributions at various radial positions of the thrust plate at different rotor speeds under the same static load of 100 N. It shows that the temperature of the thrust plate first increases and then decreases in the radial direction, and the highest temperature position is closer to the outer radius boundary. With the increase in rotor speed, the distance from this position to the outer radius boundary tends to become larger. This is because part of the heat is dissipated through forced convection from the cylindrical surface at the thrust plate outer radius, so the gas film temperature will decrease in this area to some extent.