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

Abstract

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 model referred to as Type-B was used in [6]. Both types comprise an inlet (the portion painted yellow), an impeller (green), a volute (blue and pink), and a gap of 0.025 mm (see inset).…”

“…To simulate fluid flow in the pump, and calculate the velocity, the pressure, and the fluid force, we use a general-purpose thermal fluid analysis software, "FLUENT" (produced by ANSYS, Inc.) already used in our previous study [6]. Table 1 shows the number of grid points for each part separately and the total number for the two model types.…”

“…The other conditions for the simulations are the same as those used in [6]. Average values and standard deviations are calculated over five rotations, when the flow in the pump is considered to have reached a quasi-steady state.…”

“…Positive values indicate a forward current, and negative values a backward current. Note that the total flow rate I φ exceeds the outlet flow φ because the flow traversing the gap from the volute to the inlet (leakage flow) re-enters the impeller [6].…”

“…This indicates that some energy at 233 Hz is transferred to 467 Hz as a result of having an odd number of blades (Z I =7), which causes a decrease in the pressure deviation exerted on the blades. 6. Pressure and flow in the volutes In these regions, the pressure for Type-A is larger than for Type-C because the volute cross-sectional area in Type-A is smaller, and a higher pressure is required to overcome the higher fluid resistance.…”