New Role of Oil Dewetting to Promote Lubrication under Starved or Limited Lubricant Supply Conditions
DescriptionIf lubricant supply is adequate, bearings will run under fully flooded conditions and furtherincreasing lubricant supply will not affect the lubricating film thickness. However, when underlimited lubricant supply (LLS) conditions, the starved film thickness is dependent upon theavailable lubricant volume. Most bearings operate, particularly at high speeds, under starvedconditions due to LLS. For the lubrication of micro devices or MEMS, LLS is favorablebecause any viscous resistance from excessive lubricant is not tolerated. Thus, to increase oilreplenishment to the inlet of a bearing is beneficial to the lubrication under LLS, and it is themain focus of this proposal.This proposed study is motivated by the interesting results of our recent experiments conductedusing a base oil with a small quantity of ionic liquid (IL) as additive on a slider tester. Thelubrication track changed to oleophobic, probably due to the adsorption of IL. Tiny oil dropletswere formed on the lubrication track by oil dewetting. It was unexpected to see an apparentincrease in the lubricating film thickness because it is contradictory to the general perceptionthat poor wettability of the surface hardly obstructs the outflow of lubricant from the lubricationtrack, thereby leading to decrease in lubricating film thickness.The apparent increase in film thickness is related to the oil dewetting phenomenon. It forms anew mechanism for promoting LLS lubrication via oil dewetting. The oleophobicadsorption layer, which is formed in situ, can be restored through self-healing when it isremoved during the bearing operation. Therefore, the effect is long lasting and can be literallymaintained to the end of the lubricant’s life. The ultimate goal of the project is to devise anew, effective and robust strategy to promote lubrication for LLS bearing contacts, byinnovatively utilizing a long lasting liquid-solid interface design on the lubrication track.To achieve the ultimate goal of this project, we must explore several fundamental issues: 1)understand and accurately model the oil dewetting phenomenon, including effects of thepressure and flow fields in bearing contacts; 2) elucidate the oil replenishment process, i.e. howthe size (inertial resistance) and distribution of the oil droplets and the surface tension of thebase oil affect the process; and 3) optimize the key parameters for the oil dewetting andreplenishment process for LLS lubrication.We will perform detailed experimental work and numerical simulations to understand andsolve these fundamental problems.The key deliverables of this project are: 1) an in-depth understanding of oil dewetting with ILadsorption to enhance oil replenishment; 2) a surface modification process through IL additiveto increase lubricating film generation under LLS; and 3) a new strategy based on oil dewettingto promote LLS lubrication.
|Effective start/end date||1/09/19 → …|