# Characteristic Analysis of Bump Foil Gas Bearing Under Multi-Physical Field Coupling
## 3 Case Study
### Thermal Characteristic Analysis
Figure 13 shows the gas film temperature distribution under different eccentricities. It can be clearly seen that the high-temperature concentration area changes with the change in eccentricity, and with an increase in eccentricity, the gas film temperature also increases. At the same time, it can be seen that with an increase in eccentricity, the high-temperature area is more concentrated. Figure 10: The temperature distribution of a gas film cross-section. Figure 11: (**a**) A positive plane diagram of the temperature distribution of the split gas film in the middle plane. (**b**) A reverse diagram of the temperature distribution of the gas film on the middle surface. (**c**) A circumferential gas film temperature law diagram of the middle plane. (**d**) The gas film temperature distribution in the middle plane bearing area. Figure 12: Variation in maximum pressure and maximum temperature of gas film with rotating speed. Although air bearings have the characteristics of low friction and low loss, the influence of temperature on the performance of an air bearing cannot be ignored in actual operating situations. Due to the high speed of operation, the heat generated causes the temperature in the bearing to rise, and its performance is affected. Figure 14 below shows the influence of eccentricity on the maximum dimensionless gas film pressure and load under the condition of 40,000 r/min, both considering temperature and not considering temperature. Figure 14a shows that, considering the influence of temperature, the maximum gas film pressure becomes larger under different eccentricity working conditions; Figure 14b also shows that, considering the influence of temperature, the load becomes larger. By calculating the maximum film pressure difference between the values obtained when considering temperature and not considering temperature, it is found from Figure 15 that with a change in eccentricity, the influence intensity also changes. The larger the eccentricity is, the larger the calculated pressure difference is, and the greater the temperature influence is. Similarly, the impact on the load is the same as the pressure, and with an increase in eccentricity, the impact is greater. There are various scenarios for the application of air bearings, such as in-air circulation machines, hydrogen fuel cell compressors, fuel-free turbine blowers, etc. The working environments of these machines are different, and the ambient temperatures are also very  
Figure 14: (**a**) Considering the influence of temperature on the maximum pressure of the gas film under different eccentricities. (**b**) Considering the influence of temperature on the bearing load under different eccentricities. Figure 13: (**a**) The temperature distribution of the middle surface gas film with an eccentricity of 0.44. (**b**) The temperature distribution of the middle surface gas film with an eccentricity of 0.64. (**c**) The temperature distribution of the middle surface gas film with an eccentricity of 0.84.  
different. Therefore, it is necessary to consider the influence of ambient temperature on the performance of air bearings, especially their bearing capacity and stability. Figure 16 shows, within a certain range, the influence of ambient temperature on the maximum temperature and load of the gas film. It can be seen that as the ambient temperature increases, the maximum temperature of the gas film continues to rise, and the increase rate gradually decreases and tends to a stable value. Because of the greater temperature difference between the ambient gas and the gas running in the bearing, the gas temperature in the bearing decreases after mixing. When the temperature difference is small, the temperature of the gas film increases. Because the rotor surface is affected by the cooling air flow, the rotor surface temperature is basically determined, which leads to an increase in the ambient temperature which has little effect on the film temperature. Figure 16: Effect of ambient temperature on maximum temperature and load of gas film.