Contents I. Introduction
Rarefied gas flow inside the air bearing of the head-disk interface (HDI) is in the high Knudsen number (Kn) regime. The continuum hypothesis becomes invalid at high Kn and therefore other methodologies than conventional Navier–Stokes equations should be applied to predict the rarefied motion of gas flow. In this flow regime, accurate modeling of velocity slip on the wall is critical for the performance estimation of air bearings as the fly height of the head over the disk is much less than the mean free path of the ambient gas. Several models have been developed which incorporate the molecular rarefaction effect to describe the slip flow using Kn and surface accommodation coefficient [1]–[3]. To incorporate Kn dependence in the modified Reynolds equation (MRE), several modifications to the correction coefficients have been made. Among them, the model that Kang et al. [3] proposed is a new molecular gas lubrication equation which provides an accurate database for correction coefficients and is valid for arbitrary boundary conditions and Kn. The MRE is accurate but it is not adequate for the integrated HDI simulation which includes the air bearing and lubricant film. As the slider fly height becomes much lower for high areal density, the surface morphology of lubricant film is critical for the stability of the air bearing. Molecular dynamics for the lubricant layer can be incorporated with the LBM for the air bearing to investigate the system stability. The easiness of programming/parallel computing and the computational efficiency are other advantages of the LBM over the MRE.
