Linking theory and measurements of tracer particle position in suspension flows

Methods to observe erratic motions in suspension flows are described and related to a model of axial dispersion by Van Den Broeck (1990). Experimental trials used flows of 0.46 micrometer (μm) beads in dilute suspension and tracer erythrocytes in 25% (vol/vol) erythrocyte suspension flows through 20-cm long, 50 or 100 μm high rectangular channels with 10:1 aspect ratios. Erratic motions of tracer particles in the last 10 cm were recorded on videotape with relative axial motion of the channel and camera. Motions were quantified by measuring the time intervals from when individual particles appeared stationary until they had displaced forward or backward selected net axial distances. Using the average times to move through the selected distances, an assumed parabolic flow, and formulae published by Foister and van de Ven (1980), effective dispersion coefficients were estimated and found in agreement with published data. Shapes of the curves of the square of the net distance moved vs. average time were the same for both dilute and concentrated suspensions.