Application Of Rarefied Gas Dynamics To The Head Disk Interface In Hard Disk Drives

To compete with solid state drives (SSDs), hard disk drives (HDDs) must improve their performance in capacity, speed and reliability, which requires the spacing between the magnetic disk, used to store information, and the magnetic transducer, used to read information from and write information onto the disk, to decrease. This distance is now approaching 5nm, and, accordingly, the distance between a slider, embedding the transducer, and the disk ranges from several nanometers to several micrometers, which makes the gas flowing between the slider and the disk rarefied. This dissertation applies rarefied gas dynamics to investigate several issues related to HDDs' performance. Particle contamination on the slider may scratch the disk and induce loss of data. An improved model is proposed to numerically study particle contamination on a thermal flying-height control (TFC) slider, which adjusts the transducer-disk spacing by use of a small heater embedded in the slider near the transducer. It is found that the currently used model is sufficiently accurate despite its simple form. The temperature increase inside HDDs during operation may affect their reliability. This dissertation derives an analytical formula for the gas-flow induced shear force in the head-disk interface (HDI) and uses it to investigate how the raised temperature affects the slider's flying attitude and the shear forces on the slider and the disk. Numerical prediction of a TFC slider's flying performance lays the foundation for commercial designs of TFC sliders. An improved model is proposed to calculate the heat flux on the TFC slider and it is found that the currently used model is accurate enough for this purpose. Finally, a general approach is proposed to numerically investigate a TFC slider flying in gas mixtures.