Analysis of the effect of collisions on the gravitational motion of large particles in a vertical duct

Experimental and numerical investigations of the gravitational motion of la rge particles in a vertical duct have been carried out in order to improve the knowledge of particle-to-particle collision effects in gas-solid confin ed flows. An experimental facility, consisting of a collisional flow of lar ge spherical glass particles (3 mm in diameter) in a vertical convergent ch annel has been set up. Particle flow characteristics were investigated by m eans of a photographic technique of visualization combined with image analy sis. Experiments have been performed with two particle mass flow rates corr esponding to solid volume fractions of 6.5 x 10(-4) and 1.9 x 10(-3). A sig nificant effect of the collisions between particles upon the evolution of s ome of the characteristics of the flow has been experimentally shown. Parti cle-wall collision properties have also been measured in order to provide c oefficients of the collision model used in a three-dimensional Monte Carlo type Lagrangian simulation code, Particle-to-particle collisions have been taken into account by means of the probabilistic collision model. The compa rison of measurements with predictions of the Lagrangian simulation code sh owed the suitability of the probabilistic collision model. However, the nec essity for a better knowledge of particle-to-particle collision frequency, as also for an accurate knowledge of particle-wall collision properties, is pointed out. Non-negligible effects of spin-induced forces on large partic les have also been observed. (C) 2000 Elsevier Science Ltd. All rights rese rved.