Differential pressure along the axis and local solids concentration in the fully developed region were measured in a high-density downer (0.025 m i.d., 5 m high). Chaos analysis was used to study the non-linear and multi-scale flow behavior in the downer. Local solids concentration measurements and global differential pressure measurements in the fully developed region were used to estimate the correlation integral. Pressure fluctuations in the fully developed region of the downer showed bi-fractal behavior. Large-scale behavior corresponded to a low correlation dimension, and small-scale behavior corresponded to a high correlation dimension. FCC particles showed more significant bi-fractal behavior than glass beads. Local flow dynamics from solids concentration measurements were contributed by solids flow of many different scales, namely dispersed particles and clusters of different sizes, so that there was only one scaling region in the log-log plot of correlation integral versus distance. Solids flux was found to significantly affect the correlation dimension. (c) 2005 Elsevier B.V. All rights reserved.