# Thermal Characteristics Study of the Bump Foil Thrust Gas Bearing
## 1 Introduction  
Dynamic bump foil gas bearings have been developed since 1960s, and numerous scholars have conducted the researches of related lubrication theories and experiments [1; 2]. Nowadays, requirements of larger power density performance are put forward for the turbomachinery, such as blowers, air compressors, and turbochargers, which indicates that gas dynamic thrust bearings need to work under the conditions of higher speeds, larger axial loads, and harsher environments [3]. Compared with traditional gas bearings, bump foil type gas bearings have many significant advantages, such as long operating life, high reliability, large carrying capacity, high speed and high temperature resistance, and good impact resistance. As the rotational speed gradually increases, the elastic foil structure of the bearing deforms, thereby forming the corresponding air film thickness, which has strong adaptability. Therefore, more and more researchers pay attention to the dynamic bump foil gas bearing, which are widely used in a variety of high-speed rotating machinery [4]. Under operating conditions, the ultra-high speed of the rotating thrust plate drives the gas in the clearance to move fast. Due to the viscous friction and gas compression effect between the gas films, the temperature of the bearing will increase sharply. It is insufficient to maintain an ideal temperature inside the bearing only by relying on the bearing self-cooling effect. With the accumulation of high temperature, the air film gap will decrease obviously due to the effect of thermal expansion of the structure, and the wear-resistant coating of the top foil will be damaged, which will eventually cause disastrous damages to the whole rotor system. In recent years, many impressed studies on the thermal characteristics of gas bearings have been published. [PERSON] et al. applied the Couette approximation method to solve thetemperature field distribution of journal foil gas bearing by coupling the simplified energy equation and the Reynolds equation. However, the calculation model did not consider the heat transfer between the foil structure and rotor [5]. [PERSON] et al. coupled solved the non-isothermal Reynolds equation, gas film thickness equation that considers foil deformation and thermal expansion, and the gas film energy transfer equation. The simulation results of temperature field distribution under the symmetric arrangement of two thrust bearing are obtained, and the influences of rotor speed, bearing load, and cooling air pressure on the bearing temperature are explored [6]. [PERSON] conducted the thermal-influenced loading experiments based on three corrugated foil thrust bearings with the same size. It was pointed out that the bearing load capacity increases almost linearly with the increase in rotating speed without thermal failure and decreases with the increasing rotor speed when the thermal runaway occurred [7]. [PERSON] et al. calculated the temperature field of thrust bearing by using Couette approximation method, and pointed out that the gas leakage of bearing clearance mostly occurs in the inclined area and leads to the lower temperature. In addition, the study pointed out that more than 70% of the heat generated by gas film can be removed by controlling the cooling flow rate. Meanwhile, the simulation results were compared with [PERSON]'s experimental results, the bearing loading curves in comparison are more consistent when the rotate speed is lower, and there are certain errors when rotor speed is higher. The author speculates that bearing thermal runaway occurred at higher speeds, resulting in a lower load capacity with speed increased [8]. [PERSON] et al. present the formulas for calculating the thermal resistances between the bump foil and top foil, and between the bump foil and bearing housing. The authors also considered the thermal expansion of the thrust disc, and the temperature field distribution was solved by multi-field coupling methods.