An experimental study of the motion of concentrated suspensions in two-dimensional channel flow. Part 1. Monodisperse systems

Abstract

A modified laser-Doppler velocimetry method is utilized to measure fully developed particle velocity and concentration profiles, as well as the mean-square amplitudes of velocity fluctuations (i.e. one component of the so-called particle temperature), for concentrated monodisperse suspensions across the narrow gap of a rectangular channel. A stable index-of-refraction match of the suspending and particulate phases in conjunction with short-focal-length focusing optics has enabled data acquisition up to particle volume fractions of 0.50. In general, the particle concentration distributions possess a maximum near the channel centreline and a minimum at the channel walls. Coupled to these concentration distributions were blunted velocity profiles, and particle velocity fluctuation distributions that had a sharp maximum at gap positions approximately 80% of the way from the channel axis towards the walls. The particle velocity distributions were consistent with the absence of slip between particles and the suspending fluid.The experimental data were compared with theoretical predictions from the diffusive flux model (Leighton & Acrivos 1987; Phillips et al. 1992), a model due to Mills & Snabre (1995), and the suspensions balance model (McTigue & Jenkins 1992; Nott & Brady 1994). The influence of bulk particle concentration, suspension volumetric flow rate, and ratio of channel gap width to particle diameter on the fully developed profiles was qualitatively consistent with the theoretical predictions from all three models. For the diffusive flux and suspension balance models, we used both literature values for model parameters, and values obtained from a best fit to our entire set of experimental data. Overall, the Mills & Snabre and suspension balance models were found to provide a better quantitative fit to the experimental data than the diffusive flux model.