Phenomenological study of saltating motion of individual particles in horizontal particle-gas systems

A comprehensive use of particle-fluid conveying systems for a wide range of industries requires a deep understanding in all interactions of the particular conveying process. One of the most common particle motions occurring in conveying systems is the saltating motion of particles. Although the literature abounds with theoretical, empirical and numerical studies that investigate the saltation phenomenon, there remain many questions and misunderstandings. Some of the recently solved issues are: which non-dimensional groups are introducing the particle saltating motion, how the saltation length might be predicted, how the pipe diameter and the coefficient of restitution influence the saltation velocity and length. The present work investigates the motion of individual saltating particles and presents a wide range of experimental measurements of the conveying length for a variety of particulate solids, sizes and shapes. The total conveying length was divided into three lengths: the first flight, the rebound and the rolling/sliding and each one of them is theoretically and empirically analyzed and compared. This phenomenological study presents the theoretical evidence to previously empirical findings. The theoretical analysis is further used to define the border conditions between various mechanisms. The results show that for coarse particles the rebound and rolling/sliding motions might be presented by a simple relationship between the Reynolds and Archimedes numbers. Additionally we find that the preferred saltation mode of fine powders depends on the conveying system length and diameter. For example for large pipe diameters and short length the first flight mode is the dominant; however, for small pipe diameters and long systems length the rebound mode is the dominant.