Abstract
In the pneumatic transport of coarse particles, such as wheat grains and polyethylene pellets by a horizontal pipeline, the distributions of particle concentration in the vertical plane as well as in the horizontal were detected by taking pictures of flowing particles using a strobo-camera in the region of established flow at different conditions. On the other hand, the air velocity distributions in the solid-gas two-phase flow were also measured by a small Pitot tube.
Based on the specific settling velocity of a particle in the turbulent shear flow of the Couette type, a theoretical equation for the vertical distribution of solids in steady-state was derived from the state of equilibrium between the upward rate of particle diffusion due to their collision and the downward mass rate of particle transfer per unit area due to gavity in the field. The upward particle diffusion was thought to be attributed to particle-to-particle collision as well as to particle-to-wall impact.
Using the model equation that the authors derived, the experimental data were analyzed, and reasonable equation for the vertical distribution of particle concentration shown in Figure 4 was obtained. Favourable agreement was found between expermental data and the equation when the solids-gas flow ratio is larger than 2, which means that the turbulence in the pipe was presumably largely controlled by the solids.
