Analysis of Plasma Skimming within a Hydrodynamic Bearing Gap for Designing Spiral Groove Bearings in Rotary Blood Pumps.

The blood damage problem inside the narrow hydrodynamic bearing is potentially considered to be solved by applying plasma skimming. However, the consideration of improving plasma skimming has not been included in the design of hydrodynamic bearings. The absence of experimental investigation on revealing the relationship between blood flow and plasma skimming in the bearing gap impedes the design of groove shape for plasma skimming. Thus, the present study was undertaken to evaluate how the blood flow direction and the groove shape affect plasma skimming in the bearing gap. To this end, blood tests using porcine blood were repeated three times with a hematocrit of 0.8%. The bearing gap during the tests was adjusted to 25 µm and the rotational speed was adjusted from 50 rpm to 2500 rpm. The blood flow and plasma skimming effect was evaluated based on image analysis utilizing a high-speed microscope. Results of three tests indicated that the flow direction of RBCs was dominated by the rotating surface in the bearing gap when the rotational speed increased over 1200 rpm. The best plasma skimming effect was observed when the angle between the flow direction of RBCs and the tangent line of the groove was within -10 degrees to 10 degrees. The future study will be conducted with including the consideration of plasma skimming in the bearing shape design. The findings in this study aid the future design and development of hydrodynamic bearing for use in rotary blood pumps.