Design of Mechanical Bearings in Cardiac Assist Devices
2. Hydrodynamic Lubrication
As indicated in Figure 1-3, there are two types of bearing configurations: (1) thrust bearing to support the normal load and (2) journal bearing to support the radial load. Often separate thrust and journal bearings are designed and implemented to support a rotating impeller. In certain cases more complex designs are used to combine the two bearing types. Nevertheless, the basic geometry that makes load support possible in hydrodynamic bearings is a converging wedge. In other words, the fluid is pulled into a converging gap through shear and a force perpendicular to the flow direction is produced, providing load support. Analysis of flow and prediction of load carrying ability of bearings starts with the Reynolds equation.