Applicability of Narrow Groove Theory in Designing Washout Features for Rotary Blood Pumps

High and low shear regions in rotary blood pumps require sufficient washout flow to minimize blood residence time, thereby preventing hemolysis or regions of stasis that can lead to pump thrombosis. Spiral groove bearings (SGBs) both enhance pump washout and reduce erythrocyte exposure to high shear. Narrow groove theory (NGT) has been used as an analytical tool to estimate the flow performance of a flat SGB during the design stage. However, NGT cannot accurately predict the performance of a conical SGB. In this study, we formulated an analytical model from the established NGT by adding an inertia correction term to incorporate variations in centrifugal force, which improved washout prediction in a conical SGB. The modified NGT model was then validated by comparison with experimental results. The results show that the modified NFT analytical model can reasonably predict washout rate when the spiral groove geometry favors creep flow conditions. The conical half angle of the SGB had the most significant impact on washout, with a decrease in half angle leading to large increases in wash-out flow. Small half angles also maintained viscous pumping at larger Reynolds numbers. In summary, the modified NGT can be a useful tool for designing conical SGBs for rotary blood pump washout within the creep flow regime.