Experimental determination of heat partition in elastohydrodynamic contacts

Experimental and theoretical analyses are reported to study the heat generation and partition in an elastohydrodynamic rolling/sliding point contact. Heat is generated within the lubricant in the Hertzian region by shearing and compression of the oil film. This heat is essentially conducted to the contacting surfaces as the amount convected from the Hertzian zone by the lubricant can be neglected due to the very low lubricant mass flowrate. A two-disk test rig was used for the experimental tests using crowned, superfinished 76.2 mm diameter disks fixed on parallel shafts. Each disk was fitted with six thermocouples in two rows of three located 3 mm and 6 mm below the surface to measure the temperature distribution of the disks during the tests. In addition, the disks were insulated on both plane sides by ceramic washers to minimise heat transfer to the surroundings over those surfaces. A numerical model was developed to calculate the circumferential mean disk temperature distribution in the outer 6 mm annular ring using the inner row of thermocouples to provide a boundary condition. The model was used to predict the temperature distribution for given values of the fraction of the total heat entering the fast disk, β, and the heat transfer coefficient, h, for the disk running surfaces. Minimisation of error between predicted and experimentally measured temperatures at the thermocouple positions, together with consideration of the physical relationship between fast and slow shaft heat transfer coefficients led to the conclusion that β lies in the range 0.71–0.77 for the experiments reported in the paper and that approximately 75% of the frictional heat dissipated within the lubricant film flows into the faster disk. This result indicates that the likely mechanism of heat dissipation within the lubricant film is by slip at or near the faster surface and that consideration of heat partition is a more discerning judge of lubricant rheological behaviour than the usual consideration of traction measurements alone.