Fluid Dynamic Forces Acting on the Rotor of a Shaft-Less Miniature Pump

For a miniature pump used in many social fields, it is expected to be able to operate without any shaft and mechanical bearing. Recently, a double-suction shaft-less miniature pump has been developed at the Lab of Multiphase Flow and Biomechanics, Tsinghua University. Because the rotor of the miniature pump is rotating inside the pump casing, a fluid dynamic bearing is necessary to support the pump rotor. In this paper, a fluid dynamic bearing was designed to support the rotating impeller and motor rotor, and was manufactured combined with the miniature pump. In order to evaluate the bearing capability, the numerical simulation based on Reynolds equation was conducted for the fluid dynamic bearing. Both the performance experiment of the pump and the numerical results for the bearing indicate that the fluid dynamic bearing designed for the miniature pump in this study is usable and reliable. It is also noted that the performance including the liquid film thickness distribution, static pressure distribution, bearing capability, etc. of the bearing has been reasonably predicted using the present numerical methods. Further, the bearing capability increased remarkably with eccentric ratio between the bush and journal, and rotational speed of the pump for the fluid dynamic bearing.