The rectangular-cross-section blades of a centrifugal secondary impeller in a ventricular-assist blood pump would be replaced with blades of wavy cross section, according to a proposal. As explained below, the resulting modification in the flow pattern would reduce the tendency toward clotting.
The function of the secondary impeller in a centrifugal-assist blood pump is to deliver a flow of ≤0.1 liter per minute through a fluid film bearing. The wavy-blade concept would be primarily advantageous at flow rates ≤0.1 liter per minute, but could also be applied, if necessary, to blood-pump impellers with nominal flow rates as large as 5 liters per minute, in cases in which blood would otherwise coagulate on blades, forming deposits that would eventually grow to block flow passages.
The figure illustrates the older and the proposed newer designs. In the older design, the square corner regions of the passages between the blades accommodate the formation of pockets of recirculation, which can cause coagulation and deposition of blood on the blades. Recirculation also gives rise to long residence times within the passages, thereby triggering the onset of coagulation within the blood and increasing the deposition on the blades.
The adoption of the proposed wavy (nearly sinusoidal) cross sections of the proposed impeller blades would effectively reduce the sizes of the corner regions, reducing the tendency for pockets of recirculation to form. The average thicknesses of the wavy blades would be greater than those of the rectangular blades; in other words, the cross-sectional areas of the passages between blades would be reduced. As a result, the residence time for a given flow rate would be reduced.
The Wavy-Blade Design would eliminate the square corner regions where recirculation tends to occur, and would reduce the flow cross section, thereby reducing residence time.
This work was done by Joseph P. Veres of Lewis Research Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Machinery/Automation category.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Lewis Research Center
Commercial Technology Office
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Refer to LEW-16447.