Department of Cardiovascular Engineering, Institute for Applied Medical Engineering, RWTH Aachen University, Aachen, Germany.
Artif Organs. 2013 Oct;37(10):913-20. doi: 10.1111/aor.12076. Epub 2013 May 2.
Rotary blood pumps (RBPs) have demonstrated considerable promise while treating heart failure patients, such that they are being placed at an earlier stage of the disease. These devices may therefore be required to operate for prolonged durations which yields the need for RBPs exhibiting high durability, reliability, and blood compatibility. Noncontacting bearings, utilizing magnetic and/or hydrodynamic suspension techniques, appear to provide a suitable solution to these challenges. Hydrodynamic suspension has the advantage that it does not need feedback control systems. Among various hydrodynamic bearing types, the circular journal bearing has the particular benefit of easy manufacturing. This study presents methods to evaluate the performance of short (length to diameter ratio <1) circular hydrodynamic journal bearings (HJBs) for RBPs. Analytical calculations with specific boundary conditions are presented to predict the rotor's eccentricity under equilibrium states and thus the related performance parameters such as load capacity, power loss, and shear rates. These results and boundary conditions were confirmed experimentally in a specially designed test set-up. The bearing performance was found to correlate to analytical solutions using the full Sommerfeld boundary condition instead of the half Sommerfeld condition conventionally used for such applications. Geometrical and operational parameter variations showed that HJB designs with a short Sommerfeld Number SS >0.02 can provide sufficient fluid film thicknesses and low shear rates. The measurements were further used to evaluate the bearings' stability. The estimation of the stability threshold drawn in relation to a modified stability index and the equilibrium eccentricity of the rotor allows the prediction of stability for short circular HJB designs under full Sommerfeld condition.
旋转血泵 (RBPs) 在治疗心力衰竭患者方面表现出了相当大的潜力，因此它们被放置在疾病的早期阶段。这些设备可能因此需要长时间运行，这就需要 RBPs 具有高耐用性、可靠性和血液相容性。利用磁悬浮和/或液力悬浮技术的非接触式轴承似乎为这些挑战提供了一个合适的解决方案。液力悬浮的优点是不需要反馈控制系统。在各种液力轴承类型中，圆形轴颈轴承具有易于制造的特殊优点。本研究提出了评估用于 RBPs 的短（长径比 <1）圆形液力轴颈轴承 (HJB) 性能的方法。提出了具有特定边界条件的分析计算，以预测转子在平衡状态下的偏心率，从而得出相关的性能参数，如承载能力、功率损耗和剪切率。这些结果和边界条件在专门设计的测试装置中得到了实验验证。研究发现，使用完整的 Sommerfeld 边界条件而不是传统应用中使用的半 Sommerfeld 条件来分析解决方案，可以使轴承性能与分析结果相关联。几何和操作参数的变化表明，具有短 Sommerfeld 数 SS >0.02 的 HJB 设计可以提供足够的流体膜厚度和低剪切率。测量结果进一步用于评估轴承的稳定性。与修改后的稳定性指数和转子的平衡偏心率相关的稳定性阈值的估计允许在完整 Sommerfeld 条件下预测短圆形 HJB 设计的稳定性。
