Prediction of Hydrodynamic Bearing Performance for Cardiac Assist Devices

H. Heshmat, A. Z. Hunsberger, S. Jahanmir, M. J. Tomaszewski, J. F. Walton, “Prediction of Hydrodynamic Bearing Performance for Cardiac Assist Devices,” ASAIO Journal, 52 (2006) 51A

Development of a reliable and efficient bearing system is one of the most critical challenges of long-term rotary mechanical circulatory support. Non-contacting hydrodynamic bearings offer superior performance to contact pivot bearings, with respect to power loss, heat generation and wear, as well as minimizing potential blood hemolysis. Hydrodynamic bearings are virtually power loss-free if the fluid film is kept relatively large and provide excellent load capacity with reducing fluid film thickness. For this reason, these bearings are an excellent option as an auxiliary bearing to be used in conjunction with a primary magnetic bearing system. In order to develop an auxiliary hydrodynamic bearing for the MiTiHeart®, several bearing configurations were designed based on the taper-land configuration. These designs were optimized based on maximizing the bearing load performance and minimizing shear stresses. In-vitro tests were performed with blood analog (glycerin/water) in a custom-built tribometer in order to measure load carrying capacity and power loss as a function of rotational speed, fluid film thickness and fluid viscosity. Theoretical results were compared to experimental data. Theoretical analysis of bearing performance was achieved by solving the steady state incompressible hydrodynamic problem (modified Reynolds equation). The results indicate a strong confidence in the theoretical results of load capacity and power loss as a function of bearing geometry, film thickness and fluid film properties.

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