Examination of Blood as a Multi Phase Fluid
Background
Typically during the numerical analysis of a blood containing device, the fluid is modeled as homogeneous, with no consideration to the separation of blood components.. However, this separation of blood components is a known effect, for example, during the flow through a capillary with a diameter less than 100µm (Fåhraeus-Lindquist effect). This phenomenon is also observed in narrow gaps, such as those found in the bearings of mechanical heart valves or rotary blood pumps. In close vicinity to these bearings, cell separation can cause a reduction in hemolysis and thus have a positive effect. Therefore the examination of blood as a multi phase fluid provides considerable insights into the hematologic impact of blood contacting devices and has the potential to provide a more accurate predictions during device development and optimization.
- Figure 1: Micro channel with a diameter of 70μm and a hematocrit value of 30%. The volume flow is less than 0.1 ml / h; the cellular component is visible
Methods
Micro channels with different geometries are perfused with blood; the diameters of these channels vary from 50 µm to 350μm. Using a digital microscope, images are taken of the blood flow and are evaluated by gray scale analysis using Matlab. Areas with a high proportion of erythrocytes appear darker than plasma rich areas. The gray scale intensity profile of the images are systematically investigated as a function of various hematocrit values, flow rates and geometry variations.
