| Hemolysis is the most important blood trauma in rotary pump and one of the key problems for its clinical use. In this paper, theoretical analysis, CFD (Computational Fluid Dynamics), hemolysis test and PIV (Particle Image Velocimetry) were introduced to investigate synthetically the influence of impeller design on flow patterns and hemolysis levels in the streamlined impeller pump developed in Jiangsu University and US clinical Bio-pump.The main contents include:(1) A theoretical 3-dimensional streamlined design of impeller in rotary pumps was introduced. According to the special requirements of blood pumps ,the equations of continuity, motion and energy were established and solved to get the analytical expression of vane and shroud.(2) Hemolysis tests were performed in a simulating circulatory system, and the results showed that the hemolysis index of the streamlined impeller pump is 0.003 while that of Bio-pump is 0.065 in hydraulic design condition (4L/min,100mmHg).(3) Numerical methods were introduced to reveal the flow patterns in blood pumps. The parametric three-dimensional model was created by pro/Engineer for flow domains, and nonstructural grids were adopted for grid generation. In addition, k-εturbulent model and reynolds stress model were introduced to predict the flow patterns and shear stress in the pumps.(4)The simulation results for the flow-path model revealed that the flow patterns in the streamlined pump appear to be regular, the streamlines and stream surfaces were coincident with the vanes and shrouds anywhere, without evident flow separation, stagnation and re-circulation. Under the same boundary conditions, the flow separation occurred between the main flow and the straight vanes and shrouds in Bio-pump, and big swirls emerged in some areas. It was concluded that in the same boundary conditions the blood pump based on streamlined design had better hemo-compatibility and lower hemolysis level. Meanwhile, the simulation results of the whole-domain model after the interaction of the pump house and the impeller revealed the asymmetry of flow patterns in the pumps resulting from the asymmetry of the pump house. In the streamlined pump, the flow patterns in the most domain were regular while a small vortex emerged in the outlet of flow path . In the Bio-pump with straight vanes ,however, a big vortex occured in the exit of flow path and a small vortex emerged in the inlet of flow path; both covered the most domain of flow path. No regular flow patterns such as flow separation, stagnation and re-circulation were found in the pump house in both pumps due to the small clearance between impeller and the pump house.(5) Quantitative evaluation of shear stress-related hemolysis in centrifugal blood pumps was accomplished . CFD was applied to track the shear stress history of the particle streamlines while the power law model of the relations among hemolysis, shear stress and exposure time was used to evaluate the hemolysis in the pumps. The estimations showed that the hemolysis level in the streamlined impeller pump developed by Jiangsu University was lower than Bio-pump with straight vanes in the same boundary conditions, which was coincident with the experimentally measured hemolysis index and the analysis of flow patterns based on hemo-dynamics. CFD was proved to be a feasible tool to estimate the hemolysis levels in blood pumps. (6) PIV was employed to explore the flow patterns in the pumps with different impeller design in different working conditions. According to the special requirements for blood pumps ,a PIV testing platform including an external triggered synchronous system was established to measure the instantaneous velocity in the pumps. The effect of working condition and impeller design on flow patterns and hemo-compatibility was investigated based on the measuring results. It was also proved that in design conditions ,the streamlined impeller pump had better hemo-compatibility than Bio-pump.
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