Capillary Flow: History,experiments and theory

The history of capillary flow is presented from the earliest observations to the most recent experiments. Parallel theoretical developments are traced from early work on continuous fluids to modern work in which the discrete nature of each blood cell is taken into account. A comparison of theory and experiments shows that most features of capillary flow are well understood qualitatively, e.g. the variations of cell concentration and apparent viscosity with microvessel diameter. Quantitative comparisons between theory and experiments, however, are not yet possible. There is a need for the development of theoretical solution for non-axisymmetric flow of flexible particles in a capillary, as well as flow at junctions.