Direct Monte Carlo simulation of nanoscale mixed gas bearings

Kyaw Sett Myo,Kok Leong Lee,Weidong Zhou,Wei Hua,Shengkai Yu

doi:10.1177/1687814015589528

Abstract

The conception of sealed hard drives with helium gas mixture has been recently suggested over the current hard drives for achieving higher reliability and less position error. Therefore, it is important to understand the effects of different helium gas mixtures on the slider bearing characteristics in the head–disk interface. In this article, the helium/air and helium/argon gas mixtures are applied as the working fluids and their effects on the bearing characteristics are studied using the direct simulation Monte Carlo method. Based on direct simulation Monte Carlo simulations, the physical properties of these gas mixtures such as mean free path and dynamic viscosity are achieved and compared with those obtained from theoretical models. It is observed that both results are comparable. Using these gas mixture properties, the bearing pressure distributions are calculated under different fractions of helium with conventional molecular gas lubrication models. The outcomes reveal that the molecular gas lubrication results could have relatively good agreement with those of direct simulation Monte Carlo simulations, especially for pure air, helium, or argon gas cases. For gas mixtures, the bearing pressures predicted by molecular gas lubrication model are slightly larger than those from direct simulation Monte Carlo simulation.

Highlights

In the current hard disk drives (HDDs), air bearing sliders are used for positioning the read–write head above the target track of disk accurately for recording data
The distance between the transducer embedded in the head and the disk requires decreasing for higher recording density as small data bits on high density media demand small magnetic spacing to achieve it. At this nanoscale head–disk interface (HDI), a thin layer of air film is formed to support the head float over the disk, which constitutes a successful application of gas lubrication
The direct simulation Monte Carlo (DSMC) method is a promising tool for micro and nano flow simulations, and it has been validated for computing the gas flow in the air bearing interface by Alexander et al.[6]

Summary

Introduction

In the current hard disk drives (HDDs), air bearing sliders are used for positioning the read–write head above the target track of disk accurately for recording data. Liu et al.[4,5] investigated effects of various air–helium gas mixtures on the flying performance of a thermal flying-height control (TFC) slider In these papers, they used the conventional MGL equation to solve the mixed gas bearing problems with the physical properties of gas mixtures obtained from the theoretical models. The DSMC method is a promising tool for micro and nano flow simulations, and it has been validated for computing the gas flow in the air bearing interface by Alexander et al.[6] Previously, there were some DSMC simulation studies relating with the slider posture effect[7] and heat transfer effect[8] on the air bearing characteristics In these previous publications, pure argon gas was used as a working medium due to the simple monoatomic molecule structure and the ease for calculation. After comparing DSMC results with those calculated by conventional MGL model, we could validate the applicability of MGL model in solving the mixed gas bearing problems

Numerical methods and models

Findings

Conclusion