Masaaki Horie

Visualization of main and leakage flow in magnetically suspended centrifugal blood pump

Magnetically suspended centrifugal blood pump is implantable blood pump that can obtain an enough blood pressure and blood flow to assist the adult left ventricle. This blood pump has an impeller without a shaft in order to avoid thrombus formation on the shaft seal. It is important to improve the efficiency of this artificial heart pump and to develop a pump with a low-machine Reynolds number and a low-specific speed. In this study, we carried out a visualization experiment with a rotating Dove prism and concluded with a numerical analysis, focusing on the main flow and leakage flow. It was found that the main flow pattern inside the impeller was different between all vanes, and the leakage flow in the gap was non-uniform.Graphical Abstract

Computational Study of Magnetically Suspended Centrifugal Blood Pump (The First Report: Main Flow and Gap Flow)

Artificial heart pumps have attracted the attention of researchers around the world as an alternative to the organ used in cardiac transplantation. Conventional centrifugal pumps are no longer considered suitable for long-term application because of the possibility of occurrence of blood leakage and thrombus formation around the shaft seal. To overcome this problem posed by the shaft seal in conventional centrifugal pumps, the magnetically suspended centrifugal pump has been developed; this is a sealless rotor pump, which can provide contact-free rotation of the impeller without leading to material wear. In Europe, clinical trials of this pump have been successfully performed, and these pumps are commercially available. One of the aims of our study is to numerically examine the internal flow and the effect of leakage flow through the gap between the impeller and the pump casing on the performance of the pump. The results show that the pressure head increases compared with the pump without a gap for all flow rates because of the leakage of the fluid through the gap. It was observed that the leakage flow rate in the pump is sufficiently large; further, no stagnant fluid or dead flow regions were observed in the pump. Therefore, the present pump can efficiently enhance the washout effect.

Computational Study of the Magnetically Suspended Centrifugal Blood Pump (2nd Report: Pressure Fluctuation and Stability of Impeller Rotation for Different Volute Shapes)

The turbo-type blood pump studied in this paper has an impeller that is magnetically suspended in a double volute casing. The impeller rotates with minimal fluctuations caused by fluid and magnetic forces. In order to improve stability of the rotating impeller and to facilitate long-term use, a careful investigation of the pressure fluctuations and of the fluid force acting on the impeller is necessary. For this purpose, two models of the pump with different volute cross-sectional area are designed and studied with computational fluid dynamics software. The results show that the fluid force varies with the flow rate and shape of the volute, that the fluctuations of fluid force decrease with increasing flow rate and that the vibratory movement of the impeller is more efficiently suppressed in a narrow volute.

A Study on Air Jets for Sweeping Volcanic Ash on Lawn

A device for sweeping volcanic ash on lawn was designed and its capability has been tested. This lawn sweeper was installed above a conveyor belt on which artificial lawn was pasted. The ash was uniformly scattered on the lawn using a hopper, conveyed at a constant velocity to the lawn sweeper and swept by it. The lawn sweeper is composed of small air jets and an air flow in a channel above the lawn. The former lift up the volcanic ash from the lawn and the latter conveys it to the dust collector. In these experiments, the lawn velocity, i. e., scavenging speed, the velocity of air flow in the channel, the air jet velocity and the arrangement of the blow tubes are altered, and the rates of collection are examined. The effect of these conditions on the rates of collection, and the optimal conditions for a high rate of collection and uniform scavenging are clarified.