Fluid dynamic forces in centrifugal blood pump impellers are of key importance in destruction of red blood cells (RBCs) because high rotational speed leads to strong interaction between the impeller and the RBCs. In this paper, three-dimensional models of five different blade geometries are investigated numerically using the commercial software CFX-TASCflow, and the streaklines of RBCs are obtained using the Lagrangian particle tracking method. In reality, RBCs pass through the pump along complicated paths resulting in a highly irregular loading condition for each RBC. In order to enable the prediction of blood damage under the action of these complex-loading conditions, a cumulative damage model for RBCs was adopted in this paper. The numerically simulated percent hemoglobin (%HB) released as RBCs traversed the impeller and volute was examined. It was observed that the residence time of particles in the blade passage is a critical factor in determining hemolytic effects. This, in turn, is a function of the blade geometry. In addition, it was observed that the volute profile is an important influence on the computed HB% released.

Large scale distributed systems are expected to consume huge amounts of energy. To solve this issue, shutdown policies constitute an appealing approach able to dynamically adapt the resource set to the actual workload. However, multiple constraints have to be taken into account for such policies to be applied on real infrastructures, in particular the time and energy cost of shutting down and waking up nodes, and power capping to avoid disruption of the system. In this paper, we propose models translating these various constraints into different shutdown policies that can be combined. Our models are validated through simulations on real workload traces and power measurements on real testbeds. 3

This paper presents the velocity measurements in the gap between the impeller and the pump casing of a 5:1 enlarged centrifugal blood pump model at operating condition. Both the radial and tangential velocity at the gap were measured. It was found that there was no cross flow in both the radial and tangential velocity distributions at the seven radial locations. This implies that the 0.2 mm gap in the prototype should be the optimal clearance of the pump. The vector plot of the resultant velocity showed that the double volute design of the pump, especially the splitter plate that started at theta; = 180 degrees, has created a washout mechanism in the clearance gap; that is, a sector of flow ranging from theta; = 100 degrees to theta; = 190 degrees has directed strongly toward the eye while the rest of the flow in the gap is in a tangential direction. It is important that the blood should flow out of the gap through the eye instead of continuing to circulate in the clearance gap. This explains why the pump has minimum hemolysis and thrombus formation and is able to function with nominal efficiency as compared to other centrifugal pumps.

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