Disk Protrusion Measurement in a Back-Heating Study for Heat Assisted Magnetic Recording

Heat assisted magnetic recording (HAMR) is a promising technology for the next generation hard disk drives (HDDs). Understanding the heat transfer at nanoscales and implementing a proper thermal management scheme become very critical as a few heat sources and energy delivery components are compactly integrated in a HAMR drive. Recently, a back-heating experimental setup is used to study heat transfer behavior. It is found that the detection of head disk contact and head disk spacing control become more complicated in this experimental setup because the local heating generates a protrusion on the media surface. In this paper, we demonstrate a method to enhance the contact detection sensitivity significantly by modulating the head disk spacing. It shows that a light contact between the head TFC protrusion and media protrusion can be effectively detected. Thereafter, the media protrusion can be measured and the head disk spacing can be well set.

Theoretical Study on Influence of Disk Spacing on Soil Failure State of Expansion Piles under Horizontal Force

Concrete expansion pile represents a new type of high-efficiency and energy-saving variable-section filling pile and it is formed by special construction technology and equipment, this technology has been basically mature which has been gradually applied to engineering in recent years. It has high bearing capacity, small settlement and uniformity, good economic and social effect, strong anti-overturning ability and flexible design[1]. In this paper, with expansion disk spacing under bearing force as the main parameter variable, numerical simulation is carried out by ANSYS finite element software to analyze the variation relationship between horizontal displacement of the pile top, bending moment of the pile and soil stress around the pile of different disk spacing models under horizontal load, and determine the influence of disk spacing parameter on horizontal bearing capacity of the concrete expansion pile. Through the research of this paper, the influence of failure mode of concrete expansion pile and size of the disk spacing on the horizontal bearing capacity under the horizontal load is qualitatively determined, which provides a theoretical basis for improving design theory and practical application of concrete expansion pile.

Head Disk Spacing Effect on Heat Transfer in Heat Assisted Magnetic Recording

Heat transfer at nanometer scale attracts a lot of interest from both academia and industries. The hard disk drive (HDD) industry cares about the heat transfer between the head and disk, as several heating and thermal sensing elements are integrated into the HDD system. Understanding the heat transfer mechanism and its dependency on spacing becomes very critical for heat assisted magnetic recording (HAMR). In this paper, we propose a new method to study the head disk spacing effects on heat transfer by introducing a small perturbation to the spacing while maintaining the heating source unchanged. The dependency of heat transfer on the nanoscale spacing provides insights to the understanding of heat transfer mechanisms inside the nanoscale gap.

Method to Design a Hydro Tesla Turbine for Sensitivity to Varying Laminar Reynolds Number Modulated by Changing Working Fluid Viscosity

There has been a recent surge in interest for Tesla turbines used in renewable energy applications such as power extraction from low-quality steam generated from geothermal or concentrated solar sources as well as unfiltered particle-laden biomass combustion products. High interest in these bladeless turbines motives renewed theoretical and experimental study. Despite this renewed interest, no systematic Tesla turbine design process based in foundational theory has been published in the peer reviewed engineering literature. A design process is thus presented which is flexible, allowing an engineering designer to select and address goals beyond simply maximizing turbine output power. This process is demonstrated by designing a Tesla turbine where Reynolds number can be easily varied while holding all other parameters fixed. Tesla turbines are extremely sensitive to inter-disk spacing. It is therefore desirable to design the experiment to avoid turbine disassembly/reassembly between tests; this assures identical disk spacing and other parameters for all tests. It is also desirable to maintain similar working fluid mass flow rate through the turbine in all tests to minimize influence of losses at the nozzle impacting shaft power output differently across experiments. Variation in Reynolds number over more than two orders of magnitude is achieved by creating a set of two-component working fluid mixtures of water and corn syrup. Increasing mixture mass fraction of corn syrup achieves increased working fluid viscosity but only small increase in density with a corresponding decrease in working fluid Reynolds number. The overall design goal is to create a turbine that allows modulating Reynolds number impact on Tesla turbine performance to be evaluated experimentally. The secondary goal is to size the turbine to maximize sensitivity to changes in Reynolds number to make experimental measurement easier. The presented example design process results in a Tesla turbine with 8-cm-outer-diameter and 4-cm-inner-diameter disks. The turbine will be able to access a range of Reynolds numbers from 0.49 < Rem < 99.50. This range represents a Reynolds number ratio of Rem,max/Rem,min = 202.8, more than two orders of magnitude and spanning the lower part of the laminar range. The turbine’s expected power output will be Ẇ = 0.47 Watts with a delivered torque of 0.024 mN-m at a rotation rate of ωmax = 1197 rev/min. Combining the analytical equations underpinning the design process with similarity arguments, it is shown that shrinking the Tesla turbine’s physical scale drives the Reynolds number toward 0. The resulting velocity difference between the working fluid and the turbine disks gets driven toward infinity, which makes momentum transfer and the resulting turbine efficiency extremely high. In other words, unlike conventional turbines whose efficiency drops as they are scaled down, the performance of Tesla turbines will increase as they are made smaller. Finally, it is shown through similarity scaling arguments that the 8-cm-diameter turbine resulting from the design process of this paper and running liquid Ethylene Glycol working fluid can be used to evaluate and approximate the performance of a 3-mm-diameter Tesla turbine powered by products of combustion in air.

Investigation of Head Burnishing of Thermal Flying Height Control Sliders

The head-disk spacing in current hard disk drives is approximately 1–2 nm. This distance is on the same order as the peak to valley surface roughness of a typical thin film disk. If one attempts to reduce the head-disk spacing even more, intermittent contacts between the slider and the disk are more likely to occur. Intermittent contacts are undesirable since they can result in slider and disk wear, lubricant transfer or degradation of the read and write elements.

Experimental and Theoretical Study of Replenishment Speed of Depleted Scar in Submonolayer Lubricant

The evaluation of submonolayer lubricant mobility is becoming increasingly important in hard disk drives, in which the thickness of the lubricant has been reduced to one monolayer and that of the mobile lubricant layer has been reduced to less than 0.3 nm. To decrease the head–disk spacing significantly, a design concept of surfing–recording is proposed, in which a protruding small head’s surface slides on the mobile lubricant layer without solid–solid contact [1]. However, its feasibility has not yet been confirmed because the durability of the mobile and bonded lubricants with respect to the head–disk sliding contact has not been elucidated well.

Lubricant Flow and Accumulation on the Air Bearing Surface of a Hard Disk Drive

During normal operations of a hard disk drive (HDD), a slider flies over the surface of a spinning disk lifted by a thin layer of air. The disk surface is coated by a molecularly-thin layer of lubricant to protect it against corrosion and reduce wear on the read/write head. The flying height of the slider should be as small as possible in order to achieve higher recording densities. In current HDDs the head-to-disk spacing is on the order of 1–3 nm [1]. At this ultra-low spacing lubricant from the disk often transfers to the slider’s air bearing surface (ABS) forming a thin film that imposes a significant degradation on its performance. Problems such as head instabilities, flying stiction, disk lubricant depletion and increase in head-disk spacing occur when lubricant is present on the ABS [2]. To avoid this condition, modern sliders should be able to remove the lubricant from the ABS as fast as possible. Hence, it is necessary to have a thorough understanding of the lubricant flow process and its driving forces.

Experiment of a Tesla Engine for Wind Energy Capture

Tesla engine converts the fluid energy into the rotating energy by using the viscosity of moving fluid. Because this machine has high rotating speed but low torque, the application of this engine is still under discussion. However, due to environmental problem, a lot of researches focus on green energy, the air engine becomes an important research issue. The main power source of Tesla engine is compressed air. Because only the mechanical energy transformation occurs inside the engine, there is no by-product produced by the engine. In this study, this device was considered to extract power from wind energy. The viscous stress is relatively small when it is compared to drag force or pressure. Therefore, this study is to discover the possibility of this application through the experiment. The unique inlet was constructed to guide the wind into the engine’s casing. The disk spacing was also changed to discover the optimum disk spacing. The main purpose is to test the engine’s output for its application on the wind energy capture.