The Influence of Impeller Geometries on Hemolysis in Bearingless Centrifugal Pumps

Numerical simulation on the effect of impeller radial gap on hemodynamics and hemocompatibility of a centrifugal blood pump

Impeller radial gap is one of important parts within a blood pump, which may affect the hemodynamics and hemocompatibility. In this study, computational fluid dynamics method was performed to evaluate the impact of radial gap sizes. The volume of scalar shear stress decreased with radial gap sizes increasing. On the contrary, the residence time increased with radial gap sizes increasing, especially in the bottom gap. The hemolysis index and platelet activation status at three flow rates decreased with the increase of radial gap sizes. Compared with the hemolysis index when the radial gap size was 0.6 mm, the hemolysis index for the radial gap of 1.0 mm decreased by 27.6%, 25.4% and 21.1% from low flow rate to high flow rate, respectively. Similarly, the platelet activation status for the radial gap of 1.0 mm decreased by 13.0%, 11.5% and 9.1%, respectively. As a novelty, this study revealed that radial gap sizes can significantly influence the blood pump hemocompatibility, especially at low flow rate. In addition, the hemolysis performance can be more affected by radial gaps than that on thrombosis risk.

Rotating characteristics and stability analysis of unsymmetrical magnetically suspended motor

The rotating characteristic and the stability analysis of unsymmetrical magnetically suspended motor (MSM) are investigated in the article. Firstly, the dynamic functions of unsymmetrical MSM with different moment of inertia ratios and suspension span ratios are developed. Based on the equation of radial rotation, the open-loop pole and the frequency response are analyzed, so relationships among critical whirling frequency, moment of inertia ratio and suspension span ratio are established. Moreover, relationships among rotating characteristic, moment of inertia ratio and suspension span ratio are investigated, and then the rotation stability criterion of unsymmetrical MSM based on dual-frequency bode diagram is developed. Finally, the results prove that the proposed rotation analysis method is a potential way to analyze rotating characteristic of unsymmetrical MSM.

Design Method of Bearingless Permanent Magnet Slice Motor for Maglev Centrifugal Pump Based on Performance Metric Cluster

Different from ordinary AC machines, the design of a bearingless permanent magnet slice motor (BPMSM) considers not only the torque performance, but also the passive and active suspension properties. In addition, BPMSM for a maglev centrifugal pump has unique design characteristics due to the integration of the pump head and sensors. This paper investigates evaluation and design techniques based on a cluster of performance metrics targeting on developing BPMSM for a maglev centrifugal pump. The cluster of performance metrics for BPMSM, including passive stiffness (kz, kz/kx, kz/ky, kα, and kβ) and active factors (ki and cm), is first proposed and an evaluation function fiSi,Li is constructed. Then, practical configurations of BPMSM for a maglev centrifugal pump are summarized. Based on the cluster of performance metrics, the finite-element method (FEM) is used to explore the impact of the rotor magnetization (sinusoidal, diametric, and radial method) on motor properties. Subsequently, the complete design process of BPMSM for a maglev centrifugal pump is introduced and key differences (including three crucial geometric parameters: ratio of rotor height to diameter λ, magnetic gap length δ, and stator tooth width αst) in the design considerations between BPMSM and general bearingless motors are analyzed. Finally, the upgraded performance (kz, kα, kβ, ki, cm, and fiSi,Li increased by about 29%, 38%, 33%, 31%, 21%, and 15%, respectively) of the designed candidate is obtained, which verifies the effectiveness of the proposed design methods.