Abstract
Solid nanoparticles have been applied as anti-wear and friction reduction additives for lubricants. In this paper, the flow characteristics of solid particles used as additives for lubricants were studied. A flow field visualizer based on high speed photography was developed. The particle trajectories in the point contact area were recorded using the flow field visualizer and were compared with the particle trajectories simulated using COMSOL. The results were analyzed and compared with tribological test results. It was found that the experimental results matched well with the simulation results, and the speed of the particles decreased by 60% at the inlet and outlet zones of the contact area. Solid particles were found to experience an unsteady flow in both the inlet and outlet zones and this would contribute to particle sedimentation in those areas, which matches well with the findings of the tribology test, which showed that more particles sedimented in those two areas.
Highlights
Solid particles were found to experience an unsteady flow in both the inlet and outlet zones and this would contribute to particle sedimentation in those areas, which matches well with the findings of the tribology test, which showed that more particles sedimented in those two areas
The motion of particles used as additives in lubricants was simulated using COMSOL
Particles near the sliding wall were dragged by the high speed ow and the speed of the particles was about 0.5 m sÀ1 while the speed of the particles far from the wall was below 0.2 m sÀ1
Summary
Nowadays solid particles are added into lubricants for use as additives to improve the tribological properties, and the tribological performance of solid particles has been broadly investigated.[1,2,3,4,5] These solid particles exhibit good anti-wear and friction reduction properties by adsorbing on the wear surface, forming a protective lm, supporting the contact surface and repairing the rough surface.[6,7,8,9] As one of the most important and interesting topics in the study of particle tribological mechanisms, the motion of particles in the contact area, especially for point contact and line contact conditions, has been the focus for many researchers.[10,11] The motion of particle additives in uences the functioning of the particles and the tribological properties. The surface would be damaged by the particles if a large number of particles became entrapped in the contacting area, especially under point contact conditions.[12,13] it is important to study the ow characteristics of particles for use as lubricant additives. Most researchers have focused on particle motion in the inlet zone and the contact zone, and few researchers have studied particle motion in the outlet zone, particles would become entrapped or sediment in the outlet area. It is necessary to give a whole view of the ow eld in the contact area and to investigate particle motion by using both simulation methods and visualization methods. It was found that the particles aggregated and sedimented in the inlet and outlet zones on the wear surface, which matched well with the ndings
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