Incipient motion of individual particles in horizontal particle-fluid systems: A. Experimental analysis

This paper investigates the incipient motion velocity of individual particles in horizontal conveying systems. The first part presents a wide range of experimental measurements and an empirical analysis on incipient motion velocity (a type of pickup velocity) for a variety of particulate solids, sizes and shapes. Results from the literature for incipient motion of individual particles in gases and liquids are taken into account in the final empirical analysis. It was found that all the results for the single particle incipient motion velocity could be presented with a high accuracy by a simple relationship between the Reynolds and the Archimedes numbers. Furthermore, the friction coefficient should be taken into account for large particles by modifying the Archimedes number. The incipient motion velocity was added to a generalized master curve, which included various threshold velocities such as: pickup velocity from a layer of particle in gas and liquid, minimum pressure velocity, boundary saltation velocity, terminal velocity and minimum fluidization velocity. The different threshold velocities are presenting in this master curve through modified Reynolds and Archimedes numbers. The Reynolds number is modified by taking into account the effect of the pipe diameter and the Archimedes number is modified by taking into account various properties that affect each threshold mechanism. The incipient motion velocity was also compared to the boundary saltation velocity (saltation velocity of single particles) and some hysteresis was found. However, this hysteresis is larger for fine powders than for coarse particles.