Application of Rarefied Gas Dynamics to the Head-Disk Interface in Hard Disk Drives PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Application of Rarefied Gas Dynamics to the Head-Disk Interface in Hard Disk Drives PDF full book. Access full book title Application of Rarefied Gas Dynamics to the Head-Disk Interface in Hard Disk Drives by Nan Liu. Download full books in PDF and EPUB format.
Author: Nan Liu Publisher: ISBN: Category : Languages : en Pages : 206
Book Description
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.
Author: Nan Liu Publisher: ISBN: Category : Languages : en Pages : 206
Book Description
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.
Author: Yuan Ma Publisher: ISBN: Category : Languages : en Pages : 104
Book Description
Since its introduction in 1956, hard disk drives have become one of the dominant products in the industry of data storage. The capacity of the hard disk drives must keep evolving to store the exploding data generated in the era of big data. This demand pushes the development of technologies including heat assisted magnetic recording (HAMR), microwave assisted magnetic recording (MAMR) and bit-patterned media (BPM) to increase the areal density beyond 1Tb/in2. In the development of these technologies, it is essential to have a clear understanding of the dynamics and nanoscale heat transfer behavior across the head-disk interface. In this dissertation, dynamics and nano-scale heat transfer in the head disk interface are discussed. Experimental study of nano-scale heat transfer is conducted with the specifically designed static touchdown experiment. Simulation strategy that incorporates the wave-based phonon conduction theory was also developed. In the flying condition, correlation between the temperature and head disk spacing was found at both passive flying stage and modulation stage. When the flying height increases due to either disk surface microwaviness or contact induced modulation, head temperature will increase, with a slight time delay, indicating the existence of a cooling effect as the head approaches the disk. The static touchdown experiment, which decouples the complicated air bearing from the nano-scale interface was further designed and performed. The heat transfer behavior across a closing nano-scale gap between head and disk was observed and measured. Experimental and simulation results showed general agreement with the theoretical predictions of the wave based theory for radiation and phonon conduction. The effect of different factors including humidity, air pressure, lubricant layer and disk substrate in the static touchdown experiment were also studied separately. Furthermore, the dynamics of HAMR condition was studied with waveguide heads. The laser induced protrusion was found to be around 1~2 nm in height. The findings of this dissertation could be applied to future HAMR head/media design, and the static touchdown experiment could be potentially improved to be a new approach to measure material conduction coefficient and emissivity with high special resolution.
Author: Haoyu Wu Publisher: ISBN: Category : Languages : en Pages : 114
Book Description
The hard disk drive (HDD) is still the dominant technology in digital data storage due to its cost efficiency and long term reliability compared with other forms of data storage devices. The HDDs are widely used in personal computing, gaming devices, cloud services, data centers, surveillance, etc. Because the superparamagnetic limit of perpendicular magnetic recording (PMR) has been reached at the data density of about 1 Tb/in^2 , heat assisted magnetic recording (HAMR) is being pursued and is expected to help increase the areal density to over 10 Tb/in^2 in HDDs in order to fulfill the future worldwide data storage demands. In HAMR, the magnetic media is heated locally (~50nm x 50nm) and momentarily (~10ns) to its Curie temperature (~750K) by a laser beam. The laser beam is generated by a laser diode (LD) and focused by a near field transducer (NFT). But the energy and mass transfer at high temperature from the laser heating can cause potential reliability issues. The design temperature of the NFT is much lower than the media’s Curie temperature. However, the distance between the NFT and the media is less than 10nm. As a result, the heat can flow back from the media to the NFT, which is called the back-heating effect. This can cause undesired additional temperature increase on the NFT, shortening its lifetime. Additionally, depletion, evaporation and degradation can happen on the lubricant and the carbon overcoat (COC) layer of the media. The material can transfer from the media to the head at high temperature and cause solid contamination on the head, adversely affecting its reliability. Since the laser heating in HAMR happens at nanoscale spatially and temporally, it is difficult to measure experimentally. In this dissertation, a comprehensive experimental stage, called the Computer Mechanics Laboratory (CML)-HAMR stage, was built to study different aspects of HAMR systems, including the heat and mass transfer in the head-disk interface during laser heating. The CML-HAMR stage includes an optical module, a spinstand module and a signal generation/acquisition module. And it can emulate the HAMR scenario. The head’s temperature was measured during the laser heating using the stage and heads with an embedded contact sensor (ECS). It was estimated, based on a linear extrapolation, that the ECS temperature rise is 139K, 132K, 127K and 122K when the disk is heated to the Curie temperature (~750K) and the head-disk clearance is 0nm, 1nm, 2nm and 3nm, respectively. The heating effect of the ECS was also studied and a related heat transfer experiment was performed. The normalized ECS self heating temperature rise, an indicator of the heat transfer in the head-disk interface (HDI), was measured. It was concluded that the heat transfer coefficient across the HDI strongly depends on the width of the gap size, especially when the gap size is smaller than 1nm. The head disk interaction during the laser heating was studied using a waveguide head, i.e., a HAMR head without the NFT. It showed that the laser heating can cause head surface protrusion. This lowers the fly-height (FH) and results in early touchdown (TD). It was shown that the ratio of touchdown power (TDP) change to the laser current is 0.3mW/mA. The dynamics of the head also changes during the laser heating. It was found that the magnitude of the 1st-pitch-mode vibration on the head increases over time both in short term and long term. The accumulation of material transferred to the head was also investigated. It was found that the solid contamination caused by the laser heating forms in the center of the waveguide. The round-shaped contamination formed on the head surface after laser heating. Finally the disk lubricant reflow after laser heating was studied. In the experiment, a beam of free space laser shines on the rotating disk at different laser powers, disk rotating speeds and repetitions. Then the disk was examined by an optical surface analyzer (OSA). It was found that 80% of the displaced lubricant recovers within 20 minutes. A simulation was also performed. The experiments and the simulation are in good agreement.
Author: Robert W. Bruce Publisher: CRC Press ISBN: 1420069098 Category : Science Languages : en Pages : 1139
Book Description
Since the publication of the best-selling first edition, the growing price and environmental cost of energy have increased the significance of tribology. Handbook of Lubrication and Tribology, Volume II: Theory and Design, Second Edition demonstrates how the principles of tribology can address cost savings, energy conservation, and environmental pr
Author: Robert W. Bruce Publisher: CRC Press ISBN: 142006908X Category : Technology & Engineering Languages : en Pages : 1173
Book Description
Since the publication of the best-selling first edition, the growing price and environmental cost of energy have increased the significance of tribology. Handbook of Lubrication and Tribology, Volume II: Theory and Design, Second Edition demonstrates how the principles of tribology can address cost savings, energy conservation, and environmental protection. This second edition provides a thorough treatment of established knowledge and practices, along with detailed references for further study. Written by the foremost experts in the field, the book is divided into four sections. The first reviews the basic principles of tribology, wear mechanisms, and modes of lubrication. The second section covers the full range of lubricants/coolants, including mineral oil, synthetic fluids, and water-based fluids. In the third section, the contributors describe many wear- and friction-reducing materials and treatments, which are currently the fastest growing areas of tribology, with announcements of new coatings, better performance, and new vendors being made every month. The final section presents components, equipment, and designs commonly found in tribological systems. It also examines specific industrial areas and their processes. Sponsored by the Society of Tribologists and Lubrication Engineers, this handbook incorporates up-to-date, peer-reviewed information for tackling tribological problems and improving lubricants and tribological systems. The book shows how the proper use of generally accepted tribological practices can save money, conserve energy, and protect the environment.
Author: Nan Liu
Author: Nan Liu
Author: Yuan Ma
Author: Mark Joseph Donovan
Author: Ta-Chang Fu
Author: Haoyu Wu
Author: Brian Hayes Thornton
Author: Puneet Bhargava
Author: Robert W. Bruce
Author: Robert W. Bruce
Author: Du Chen