Leakage flow rate and wall shear stress distributions in a biocentrifugal ventricular assist device

In previous studies, the radial and tangential leakage flow velocities in the gap between the rotating impeller and the pump casing of a biocentrifugal ventricular assist device (VAD) model were obtained by hot wire. Based on the velocities obtained, the leakage flow rate through the clearance gap between the impeller and the stationary casing, as well as the wall shear stress distributions on the inner surface of the stationary casing, can be determined. By integrating the radial velocities numerically, the leakage flow rate through the clearance gap was found to be 6.43 x 10(-4) m3/s under operating conditions, which is 25.7% of the inlet flow. This is equivalent to approximately 1.7 L/min in the prototype. The leakage flow rate was found to be 5.22 x 10(-4) m3/s and 3.66 x 10(-4) m3/s under fully opened and fully closed conditions, respectively. The double volute design significantly affected wall shear stress distributions, with the high wall shear stress region concentrated at the beginning of the splitter plate under all three flow conditions. In contrast, the high wall shear stress region could only be observed at the cutwater in the fully closed condition. The highest wall shear stress was found to be 44.1 Pa, which is much lower than the threshold values that cause hemolysis. On the other hand, the lowest wall shear stress was found to be 21.31 Pa. This wall shear stress level is much higher than the shear stress required to disrupt aggregates of blood cells and platelets. These findings explain why hemolysis and thrombosis are at the low level in the clearance gap of this VAD.