Flow Dynamics of an Active Mixing Pump-Oxygenator

Abstract

Efficient mass exchange and simultaneous non-traumatic blood pumping of a prototype pump-oxygenator have been demonstrated. However, details of flow fields in the pump-oxygenator and their relationship to biocompatibility have not been quantitatively studied. This study was designed to identify unfavorable flow features for design refinement guidance, characterize flow field dependence on operating conditions, and provide verification data for a developing numerical model. A series of experimental studies were performed in a steady flow mock flow loop containing a glycerin-based blood analogue. Flow fields at various locations within the device housing were visualized using laser-based fluorescent particle imaging techniques over a systemic matrix of operating conditions. Residence time of blood within the pumping chamber was measured using the indicator dilution method. Unique flow features specific to the rotational porous element were observed under all operating conditions. These features included an annular region of reverse flow encircling the main axial flow at the inlet and a divergent flow at the periphery of the rotational element. Main axial flow was observed to enter only the central portion of the rotational porous element. Flow fields at the outlet section were found to be similar to those in centrifugal pumps, which are also largely dependent on operating conditions. Images of the dye dilution indicator showed well mixed flow within the pumping chamber. Residence time of blood was found to be from 2 to 12 seconds under flow rates from 5 lpm to 1 lpm at 1000 rpm. These baseline experimental results provide guidance for future improvement and serve as the basis for expanded flow visualization studies.