Studies on Rotating Disc Flow in Narrow Clearance For Low Specific Speed-Small Centrifugal Magnetically suspended Blood Pump

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This study treats with one of research subjects for development of a centrifugal blood pump with magnetically suspended impellers as an artificial heart of next generation. This kind of pump is so small, compared with conventional industrial pumps, that blood viscousity much influences on flows in the pump.Power loss due to friction and leakage in the shroud clearance is dominant. So the flow in this shroud clearance is investigated. This is so called "the problems on viscous flow around rotating disc".The following three factors influence on this clearance flow : (l) pump pressure difference between outlet and inlet, (2) centrifugal force induced by rotating disc, (3) jet pump effect induced by pump I main flow.Though the flow, in the actual pump, leaks back through the shroud clearance from outlet side to inlet side of the impeller, a part of the pump casing is modified to bypass the leak flow, then to measure flow rate and return to the inlet side of the impeller.Experimental results shows the above three effects - leakage is surpressed by centrifugal effects at high rotational speed of impeller and by jet pump effect at high main flow rate. Of cause, leakage depends on pressure difference.In addition, the pressure distributions around outer edge and inner edge of the impeller are measured as the boundary conditions. This impeller was replaced by a blind disc, and the leakage flows were compared with double volute and without volute (open outlet). This flow indicated the above mentioned two effects (l), (2) and the angular momentum effect through spiral volute.