# Thermal Characteristics Study of the Bump Foil Thrust Gas Bearing
## 4 Experimental Study  
In this paper, the test specimen of the bump foil thrust gas bearing is manufactured and assembled, as shown in Figure 16. The K-type thermocouple is applied to measuring the bearing temperature. A number of thermocouples are stick to the top foil on the back side with copper foil tape. Figure 17 shows the positions of these thermocouples for measuring the local temperature. The thermocouple wire is buried in the bump channel.  
The same number and position of thermocouples are pasted under the two centrosymmetric top foils. The temperature measuring points 1-4 are arranged at the radius of 30 mm, and points 5-6 are arranged at the radius of 25 mm. The temperature measuring point 1 is arranged under the slope section, and the remaining temperature measurement points are in the loading region. The assembly of the bearing is completed by a spot-welding machine.  
The test bench in this paper is shown in Figure 18. The actual working process of the bearing can be realized by actively controlling the speed of the motorized spindle and by loading the thrustmeter on the other side of the thrust bearing. The displacement between the rotating plate and the bearing is measured by the eddy current displacement sensor.  
Figure 15: Relationship between bearing temperature and cooling gas flow.  
In this experiment, the axial load, which is provided by the SN-500 pointer thruster produced by SUDOO company, is applied on the side of the thrust bearing to simulate the actual axial force of the system. The structure of pointer thruster is shown in Figure 19, where the limit load is 500 N and the resolution is 2 N, the pointer thruster is fixed to the antivibration platform through the supports, and the axial force to the bearing is applied by rotating the button.  
Figure 16: Physical image of experimental bearing.  
Figure 17: Temperature measuring point bonding.  
Figure 18: Thrust bearing temperature test bench.  
Figure 20 shows the relationship between the tested top foil temperature and the bearing static load at the rotor speed of 15 krpm. During the loading process, the bearing temperature increases continuously. It can be seen from the figure that the measured temperatures on points 2, 3, and 4 are significantly higher than the temperatures on points 5 and 6, and the temperature on point 1 in the slope section is lower compared with the temperatures measured on the points of the same radius. These distribution characteristics of the foil thrust bearing temperature are consistent with the simulation results. Compared with the simulation results, the measured top foil temperatures are relatively lower, which is mainly due to the unclear boundary conditions in the experiments which should be clarified in the simulations.  
Figure 21 shows the relationship between the measured top foil temperature and rotor speed under the static load of 80 N. It shows that the temperature distribution regularities of the measuring points are similar with the regularities demonstrated in Figure 20, and the overall trend of the measured temperature is the same with the simulation results, which is the temperature will rise up almost linearly with the rotational speed going up. However, the experimental data are relatively higher than the simulation data, which is probably caused by the unclear boundary conditions in the experiments which should be clarified in the simulations or due to the measurement error during the experiment.  
Figure 19: Picture of pointer thruster.  
Figure 20: Relationship between bearing top foil temperature and load.