Flow-induced vibration of a head gimbal assembly under various conditions
The flow-induced vibration of a head gimbal assembly (HGA), known as windage, is an obstacle to achieving higher track densities in hard disk drives (HDDs). We examine the characteristics of windage in this paper with the goal of enabling the development of smaller-windage HGAs. We used a 14.5-mm-length (from swage hole center to dimple) HGA in our study. The windage was measured by a laser Doppler vibrometer in a spin stand under various conditions, such as different slider radius locations (inner diameter, medium diameter, and outer diameter), disk-rotational speeds, Z heights (distance from arm to disk), and temperatures. With respect to the slider radius location, windage was much greater when the slider was on the outer diameter rather than at other positions. When the slider was positioned at a fixed location, the windage was proportional to the square of the disk rotational speed. At high temperatures, the resonant frequencies decreased and their amplitudes increased. For some resonance modes, there was an optimal Z height. These findings will be useful for evaluating HGAs and optimizing HGAs through experimental design.
Flow-induced vibration of head gimbal assembly
This is a report on ways to reduce flow-induced vibration of a head gimbal assembly (HGA), i.e., windage. The relation between flow-induced force and windage was investigated; as was a statistical approach to optimizing an HGA-arm configuration. The investigated HGAs were set between disks in a spin stand, and their windages were measured by using a laser Doppler vibrometer. The amplitude of sway mode was found to be almost in inverse proportion to the square of its frequency because the power spectrum of the airflow between disks is in inverse proportion to the square of its frequency. Miniaturizing HGAs is therefore an effective way to reduce windage because its natural frequencies then become higher. The windage measured for a HGA with a part length of 12, for example, is 40% less than that of one with a part length of 14.5 mm. Optimizing HGA-arm configurations by the Taguchi Method is also useful for reducing windage. The Taguchi Method is a statistical technique for designing products whose performance is not affected by outside conditions. We used an L8 orthogonal array in this investigation and found that optimizing the actuator arm thickness could reduce windage most effectively, the load-beam bend angle, and the arm shape. The windage of an optimized HGA-arm configuration was reduced to about one third that of the initial configuration. This knowledge will be useful in optimizing the parameters of an HGA and a head stack assembly to obtain hard disk drives with higher track densities.
Characterization of a tube-in-shell thermosyphon heat exchanger for solar water heating
Performance of a double-wall, natural convection, two-pass, tube-in-shell heat exchanger designed for use in a solar water heating system is measured. The heat exchanger is mounted along the length of a solar water storage tank. Flow of cold water on the shell side of the heat exchanger is driven solely by buoyancy forces. Hot side fluid is pumped. Flow rate, pressure drop and temperature data needed for a semi-empirical model of the heat exchanger are obtained. Performance is measured for forced convection, hot side volumetric flow rates of 0.016, 0.032 and 0.079 l/s. Temperature difference between hot and cold fluid at the inlets is varied from 0 to 75 degC. Measured values include thermosyphon and forced flow rates, temperature differences across the beat exchanger, vertical temperature distribution in the storage tank, and pressure drop due to shear on the thermosyphon side of the heat exchanger. Heat exchanger effectiveness and overall heat transfer area product (UA) are calculated. Thermosyphon mass flow rates are on the order of 0.01 kg/s. Although the low flow rates create thermal stratification of the water storage tank, they restrict energy transfer in the heat exchanger.