Flow visualization measurement for shear velocity distribution in the impeller-casing gap of a centrifugal blood pump

A flow visualization study of a centrifugal blood pump was conducted to Sin d the shear and velocity profiles in the back gap between the impeller and the casing. For a wide range of Reynolds numbers and specific speeds, it wa s found that high shear exists only in the boundary layers of the moving an d stationary walls. The velocity profile was essentially laminar. It was al so found that the total thickness of the high shear regions is 0.3 - 0.6 mm for conditions of artificial heart and the thickness is determined only by Reynolds number. Hence, it can be concluded that reducing the impeller vel ocity is the only way to reduce wall shear stress and that increasing the g ap width is not effective.