# Research Developments of Aerostatic Thrust Bearings: A Review
## 6 The Development Trends of ATBs  
Aerostatic thrust bearings are widely used in many high-tech fields. The research on ATBs is deepening, and many advances have been achieved. However, there are still some challenges with ATBs. More effort should be put into the study of ATBs.  
1. Due to the low viscosity of the gas, the bearing capacity and stiffness of ATBs are much lower than oil bearings. These shortcomings limit the further application of ATBs. It is necessary to produce ATBs with greater stiffness and greater load capacity. In the theoretical analysis of ATBs, some traditional assumptions and neglected factors must be considered. For example, in the case of low gas film thickness, the influence of factors such as surface roughness and the mean free path of gas molecules must be considered. In the case of high-speed flow, the assumption of isothermal gas flow, the influence of gas inertial effects, shock waves, and turbulent flow effects, etc., must be carefully analyzed. In addition, under the guidance of theoretical analysis, the design level of the bearing should be continuously improved. The manufacturing process and the machining accuracy of ATBs should be enhanced. The use of modern and more precise experimental methods is also critical. It is necessary to combine theoretical analysis with experimental analysis to design ATBs with higher load capacity and higher stiffness.  
2. In addition to air, nitrogen, hydrogen, and helium, other gases are also used in ATBs to meet different working conditions and needs. With the development of hydrogen and helium liquefaction equipment, the application of ATBs using special gas becomes more extensive. There is much research on aerostatic bearings, while the research on aerostatic bearings using special gas is still limited. Due to the flammability and leakage of hydrogen and the scarcity of helium, it is relatively difficult to carry out related experimental research. The relevant experimental data are even more scarce. Due to the unique physical  
Figure 16: The air turboexpander and hydrogen turboexpander using ATBs by Xi’an Jiaotong University.  
properties of special gases, their flow characteristics, load-carrying characteristics, and the stability performance of ATBs are completely different from traditional air ATBs. Therefore, more effort should be put into the research of ATBs using special gases. In addition, the corresponding protective measures should be taken during experimentation to ensure experiment safety.  
3. When gas is used as a lubricating medium, problems such as solidification at low temperature and volatilization at high temperature of oil are completely overcome. Aerostatic bearings are suitable for high- and low-temperature environments. There are many studies of ATBs in normal temperature and low-temperature environments, while the research in high-temperature environments is relatively less. In a high-temperature environment, the effects of high temperature on gas properties should be considered. In addition, the influence of high temperature on the thermal deformation of the bearings should be considered. The gas film thickness changes due to the thermal deformation of the bearing, which will affect the bearing performance.