A compact centrifugal blood pump has been developed as an implantable left ventricular assist system. The impeller diameter is 40 mm, and pump dimensions are 55 x 64 mm. This first prototype, fabricated from titanium alloy, resulted in a pump weight of 400 g including a brushless DC motor. The weight of a second prototype pump was reduced to 280 g. The entire blood contacting surface is coated with diamond like carbon (DLC) to improve blood compatibility. Flow rates of over 7 L/min against 100 mm Hg pressure at 2,500 rpm with 9 W total power consumption have been measured. A newly designed mechanical seal with a recirculating purge system (Cool-Seal) is used for the shaft seal. In this seal system, the seal temperature is kept under 40 degrees C to prevent heat denaturation of blood proteins. Purge fluid also cools the pump motor coil and journal bearing. Purge fluid is continuously purified and sterilized by an ultrafiltration unit which is incorporated in the paracorporeal drive console. In vitro experiments with bovine blood demonstrated an acceptably low hemolysis rate (normalized index of hemolysis = 0.005 +/- 0.002 g/100 L). In vivo experiments are currently ongoing using calves. Via left thoracotomy, left ventricular (LV) apex descending aorta bypass was performed utilizing an expanded polytetrafluoroethylene (ePTFE) vascular graft with the pump placed in the left thoracic cavity. In 2 in vivo experiments, the pump flow rate was maintained at 5-9 L/min, and pump power consumption remained stable at 9-10 W. All plasma free Hb levels were measured at less than 15 mg/dl. The seal system has demonstrated good seal capability with negligible purge fluid consumption (<0.5 ml/day). In both calves, the pumps demonstrated trouble free continuous function over 6 month (200 days and 222 days).
This study investigates experimentally and numerically unsteady flow fields in an axial compressor operating at high-flow rate in order to understand the flow structure in the stator row operating at windmill condition. The experimental and numerical data are compared by time- and phase-lock-averaged techniques. Additionally, unsteady vortex structure is investigated by numerical technique. At windmill condition, the incidence angle to the stator row becomes extremely negative. Therefore, large separation occurs near pressure surface in the stator passage. The experimental and numerical results indicate that a large vortex is generated in the separation area. According to the numerical results, part of the vortex migrates downstream, and the vortex produces blockage of the main stream of the stator passage. Therefore, net flow area in the stator passage becomes small so that the flow between the vortex and suction side of stator vane is accelerated. As a result, the total pressure deterioration is generated in the stator passage because the high speed flow and the vortex cause high shear.
Detailed traverse measurements of three dimensional flows and the associated losses inside a turbine rotor passage were carried out in the rotating frame of reference by using small five hole Pitot tubes. Strong secondary flows including passage vortices, a leakage vortex and various separation vortices were found to occur in the passage, and they are significantly influenced by the rotor speed, variation of which corresponds to different test incidences and blade loadings. Loss generation process in the rotor is described in relation to the migration of low energy fluids which are driven by the various vortices and their interaction at different rotor incidences.
Activities by various authors on aerodynamics and control dynamics of rotating stall in axial compressor are first traced. Then, a process of stall cell evolution in a subsonic stage is discussed based on a 2-D CFD. A few numbers of vortices grow ahead of the rotor accumulating vorticity ejected from lightly stalled blades, and eventually organize a cell of circumferentially aligned huge vortices, which merge and recess repeatedly during the rotation. Such stall disturbance is intensified on trailing side of a circumferential inlet distortion and decays on the leading side. Considering these features, a new algorithm for stall warning is developed based on a correlation between pressure waveforms at each passing of a fixed blade. A remarkable change in the correlation level at near-stall provides a warning signal prior to the stall onset with sufficiently large time margin. This scheme is applied to achieve rotating stall prevention by actuating flaps installed on the hub. The last issue is on characteristics of forward swept blade which has much increased throttle margin with decreased tip loss. A 3-D computation shows that a secondary vortex generated in suction surface mid span interacts to reduce the tip leakage vortex that initiates the stall.
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