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.
Numerical simulation of positioning error caused by air-flow-induced vibration of head gimbals assembly in hard disk drive
Unsteady airflow in an actual hard disk drive (HDD) which has a rotary actuator is numerically simulated by using LES (large eddy simulation) technique, and the aerodynamic force affecting head gimbals assembly (HGA) is estimated from the simulation. Then calculated force is fed to a structure analysis to predict the airflow-induced vibration of HGA. Lastly, we calculate the head positioning error or the head displacements for the different HGA orientations to explain and classify the mechanism of airflow-induced positioning error (i.e. windage) in HDD.
Techno-economic analysis of solar thermal power plants using liquid sodium as heat transfer fluid
Abstract Solar thermal power plants with central receiver and thermal storage are expected to be one key technology in future electricity generation, because they are renewable and due to the thermal storage independent of the current solar radiation. State-of-the-art solar power plants often use molten nitrate salts as heat transfer fluid. The use of liquid sodium instead leads to lower electricity generation costs. Sodium has a high thermal conductivity and thus large heat transfer rates are possible. Hence, a smaller absorber surface is sufficient for the same thermal power. As a result, the sodium receiver achieves a higher efficiency at lower investment cost. Additionally, the aiming strategy, which reduces the peak heat flux on molten salt receivers isn’t necessary for sodium. Even at high heat flux densities, the absorber tubes will be cooled sufficiently due to the high heat transfer coefficients. Therefore, the sodium receiver in this analysis is designed for one single aim point, resulting in a heat flux density of q mean = 1.06 MW / m 2 and q peak = 2.99 MW / m 2 . The state-of-the-art system with molten salt considers q mean = 0.51 MW / m 2 and q peak = 1.0 MW / m 2 . The presented techno-economic analysis of two sodium based concepts compared to a reference system with molten salt results in up to 16% lower electricity generation costs.