Analysis on dynamical properties of the foil bearing rotor system with the unbalanced magnetic pull

Gas foil bearings (GFBs) are widely used in synchronous motors for their splendid performance in high speed. However, its working principle can produce unbalanced magnetic pull (UMP) between stator and rotor inevitably. Based on the rotor transverse vibration, this paper analysis the influence of UMP on the dynamic behavior of the rotor system supported by GFBs. The results show that the UMP accounts for a higher proportion of the exciting force acting on the rotor system at lower speed range. And the UMP declines with the decrease of nominal clearance. It is found that UMP will advance the critical speed of rotor system. According to the simulation results, the rated speed of synchronous motor is set at 90 000 rpm, and the nominal clearance of GFBs is 8 μm. The experimental results show that the rotor system designed in this paper works stably and achieves the predetermined design goal.

Visualization of Fluid Mixing in a Microchamber on a Rotating Disk

This paper reports flow visualization experiments of fluid mixing in a microchamber on a rotating disk. The two centrifuge-driven sample fluids were brought in contact at the Y-junction microchannel and then flowed to a circular mixing chamber where the main course of mixing took place. The flow images were acquired using a micro-image-capturing unit in synchronization with the rotational motion to allow only one shot of the targeted object on the rotating disk per revolution. Both the visualization and quantification of flow images show that the mixing efficiency of the two fluids depends not only on the rotational speed but also on the depth of the channels. It is found that the mixing efficiency generally decrease with increasing rotational speed in the lower speed range (≤ 420 rpm). Beyond this lower speed range, the mixer with a larger channel depth h = 300 μm shows an increase of mixing efficiency with increasing rotational speed to reach as much as 83% at 1200 rpm. For the mixer with a smaller channel depth h = 200 μm, however, the mixing efficiency continues deceasing or becomes flat with increasing rotational speed. It is also found that the counter-clockwise rotation produces a better mixing efficiency than the clockwise rotation in the high speed range.