Cardiovascular Engineering, Helmholtz Institute, Aachen, Germany.
Artif Organs. 2013 Sep;37(9):786-92. doi: 10.1111/aor.12166. Epub 2013 Aug 27.
Assuming that blood has a constant viscosity is a common practice when designing rotary blood pumps (RBPs), where shear stresses are generally higher than in the human body. This eases the design and allows numerical simulations and bench top experiments to be performed with Newtonian fluids. However, specific flow conditions may cause a change in cell distribution leading to an apparent lower blood viscosity. It has been observed that decreasing the vessel diameters and increasing flow velocities contribute to this effect. Because a hydrodynamic bearing operates under flow conditions following this pattern, it is important to verify whether this effect also takes place when this type of bearing is applied to a RBP. Because the operation of a hydrodynamic bearing depends directly on the fluid viscosity, a local change in cell distribution in the bearing gap can be reflected in changes in the bearing performance. In this work, a spiral groove hydrodynamic bearing was tested with porcine blood in a specially built test rig. The generated suspension force, cross flow, and bearing torque were recorded and compared with the reference response when using a solution of water and glycerol. Experiments with porcine blood yielded lower suspension forces, lower flows, and lower bearing torques than when using the glycerol solution. An explanation could be a lower apparent viscosity due to inhomogeneity of blood cell concentrations. Therefore, it is crucial to consider the effective blood viscosity when designing hydrodynamic bearings for RBPs and performing experiments.
在设计旋转血泵 (RBP) 时，假设血液具有恒定的粘度是一种常见做法，因为剪切应力通常高于人体。这简化了设计过程，并允许使用牛顿流体进行数值模拟和台架实验。然而，特定的流动条件可能会导致细胞分布发生变化，从而导致表观血液粘度降低。已经观察到，减小血管直径和增加流速会导致这种效应。由于动压轴承在遵循这种模式的流动条件下运行，因此验证这种效应是否也会在将这种类型的轴承应用于 RBP 时发生非常重要。由于动压轴承的运行直接取决于流体粘度，因此在轴承间隙中局部的细胞分布变化可以反映在轴承性能的变化中。在这项工作中，使用专门构建的测试台，用猪血液测试了螺旋槽动压轴承。记录了产生的悬浮力、横流和轴承扭矩，并与使用水和甘油溶液时的参考响应进行了比较。与使用甘油溶液相比，猪血液实验产生的悬浮力更低、流量更低、轴承扭矩更低。一种解释可能是由于血细胞浓度不均匀导致表观粘度降低。因此，在设计用于 RBP 的动压轴承并进行实验时，必须考虑有效血液粘度。
