Flow visualization evaluation of secondary flow in a centrifugal blood pump.

To design a less hemolytic and more antithrombogenic centrifugal blood pump, secondary flow, i.e., vortex and turbulent flow, must be properly controlled. An irregular stream pattern is a cause of hemolysis, and good wash-out around the shaft minimizes thrombus formation. In this study, flow visualization methods were applied to evaluate secondary flow in a centrifugal blood pump. Correlation with results of in vitro hemolysis tests was investigated. Separation of the stream lines from the vanes and patterns implying the existence of vortices were observed in the impeller that showed high hemolysis. By adjustment of vane angles, these irregular patterns could be minimized, and hemolysis decreased as well. Using a similar technique, the flow pattern at the back of the impeller could be visualized, which enabled further investigation of the effects of secondary flow on thrombus formation. This flow visualization was effective in examining secondary flow patterns.