The Use of CFD for Microhaemorheometer Design

This paper on "The Use of CFD for Microhaemorheometer Design" was presented at the NAFEMS World Congress on Effective Engineering Analysis - 25-28 April 1999, Newport, Rhode Island, USA.

Summary

A microhaemorheometer is being evaluated currently as a new instrument with which the flow properties of red blood cells (RBC's) from different sources can be characterised in microchannels that simulate the geometry of human capillaries. This instrument has recently been described by Sutton et al [1]. Its central feature is a silicon chip into which numerous microchannels with dimensions typically 3 x 3 x 100 μm, inlets and outlets have been etched by a series of micromachining processes. With a constant pressure difference applied across the ends of the microchannels, the motion of about 1000 RBC's is monitored by a sophisticated imaging system and subsequently analysed automatically.
The present work describes the design of the flow passages within a new silicon chip that will allow the rheometer to operate continuously and monitor therefore the motion of a much larger number of RBC's. This will increase the preciseness of the characterisation. From the starting point of having available a design proposal for the flow passages within the new chip, the strategy has been to build on existing experience and anticipate regions where particular flow features might cause adverse operational effects. A range of computational fluid dynamics (CFD) models was developed both to assist in optimising the geometry and to confirm that such effects were absent in the final design.
A finite element-based CFD package was used to create unstructured, boundary-fitted meshes. These were well-matched to the 'angular' geometries of the micromachined forms of silicon. The flow processes investigated included sedimentation of RBC's, flow uniformity at the inlets of the microchannels and pressure change throughout the whole system.