Washout hole flow measurement for the development of a centrifugal blood pump.

Washout holes in the impeller of a centrifugal blood pump reduce thrombus formation in areas where blood is apt to stagnate, especially in the back gap of the impeller. In this study, flow through the washout holes is quantified by pressure measurement and flow visualization with a 300% scaled-up model to understand the force driving flow through the washout holes and the flow itself. When external circuit resistance is constant, pressure distribution normalized by the square of the tip speed is constant and independent of the impeller rotational speed. The ratio of the flow rate through the washout holes to the flow rate of the external circuit is also constant. When the external circuit resistance increases, the pressure difference at the washout holes between the front and back gap of the impeller increases and generates a greater flow rate through the washout holes.