Random surface roughness effect on slider microbearing lubrication

The surface of a microbearing in a microelectromechanical system (MEMS) or microfluidic device is described by a random roughness model characterised by fractal geometry. A modified Reynolds equation with velocity slip on the rough wall is used to describe the ultra-thin lubrication of the microbearing at a wide range of Knudsen number covering the slip and transition regimes. The effects of Knudsen number, bearing geometry parameters and roughness parameters on the flow behaviours, including pressure distribution, load carrying capacity, streamwise location of the load carrying capacity and shear stress, are all investigated and discussed. The results show that surface roughness influences not only pressure distribution and load carrying capacity but also shear stress distribution of the rarefied gas flow in microbearings. The flow over surfaces with higher relative roughness induces pressure fluctuation. It indicates that the effect of random surface roughness is of great significance in the analysis and design of gas-lubricated microbearings and should be comprehensively taken into account for MEMS and microfluidic devices.