Experimental validation of a thermal model of a LOx flooded ball bearing

• A cryotechnic ball bearing was tested at University of Liège.
• Bearing temperature suddenly increases when the load becomes too high.
• A numerical model is proposed in the paper in view to explain the phenomenon.
• Experimental results led to the ball bearing operating limits.

Ball bearings of turbopumps of rocket engines work in very singular conditions; they are flooded into liquid oxygen or liquid hydrogen. Therefore, the use of any conventional lubricants (oil or grease) is prescribed. Although cryogenic fluids can cool this kind of ball bearing, they cannot separate the surfaces in contact. As a result, there is a significant increase in frictional power losses. This paper presents tests performed on a cryotechnic ball bearing flooded in liquid oxygen. The test results showed that beyond a critical loading of the bearing, a sudden increase in temperature occurred. A thermal model is also put forward, in order to understand and anticipate especially the thermal instability described above.