The optimal helium fraction for air–helium gas mixture HDDs

Helium-filled drives have recently been commercialized to enable a high recording density. However, because the use of helium increases production costs, binary gas mixtures such as air–helium have been investigated. In this paper, the dominant performance metrics of hard disk drives (HDDs) are the windage losses, the flow induced vibration (FIV), the lubricant transfer and lubricant depletion. These were investigated for air–helium gas mixtures as a function of the helium fraction. The frictional torque was empirically derived in both the laminar and turbulent regimes. The windage loss and the FIV of a helium-filled drive were found to be similar to that using an air–helium gas mixture with a helium fraction of 0.75. On the other hand, the quantity of accumulated lubricant and the maximum lubricant depletion in a helium fraction of 0.75 were superior to those in a helium fraction of 1.0. Further investigation of performance metrics should be carried out. However the performance metrics considered here showed that a helium fraction of 0.75 was favorable to a helium fraction of 1.0.