Some insights into asperity temperatures in mixed-film lubrication

This paper investigates some fundamental thermal behavior of asperity contacts in mixed-film lubrication. First, the thermal interaction between the contacting asperity and the lubricant is studied. The analysis is based on transient simulations of a mixed-film contact problem under various contact conditions. The results suggest that the solid/fluid thermal interaction can be strong. The lubricant is shown to play an important role in asperity temperature. It not only generates heat through viscous shearing but also plays a role of cooling by transporting heat out of the thermally intensive asperity contacts. The interaction can significantly reduce asperity temperatures especially under high-speed conditions. The interaction also increases the lubricant temperature away from the asperity contact, thus facilitating thermal coupling among contacting asperities. Another thermal behavior of mixed-film contact studied is the effect of heat flow in the asperity contact in the direction perpendicular to the lubricant entrainment. Results suggest that the effect of this thermal side-flow is significant in low-speed contacts and diminishes when the entraining velocity becomes high. Further, the side-flow effect is much weaker in the mixed-film contact than in the dry contact and may be neglected in the modeling of complex mixed lubrication problems.