Investigation of gas–solid flow structure after a 90° vertical-to-horizontal elbow for low conveying gas velocities

The characteristics of gas–solid flow after a 90° vertical-to-horizontal elbow, where the flow in the vertical pipe is upward, were investigated both numerically and experimentally for low conveying gas velocities. The experiments were conducted in a 0.154-m ID test section using pulverized coal particles having a mean particle diameter of 50 μ. The time-averaged local particle concentration and velocity were measured using a fiber optic probe at various locations along the length of the horizontal pipe after the elbow. The effects of gas flow velocity, gas to solids mass flow rate ratio and elbow radius to pipe diameter ratio on particle concentration and velocity profiles, and deposit characteristics were investigated. Computational fluid dynamics simulations were performed to study the particle deposition characteristics. Experiments show that saltation velocity is affected by the gas to solids mass flow rate ratio and elbow radius to pipe diameter ratio. The maximum deposit thickness typically occurred near the leading edge of the deposit. Average deposit thickness decreased with increasing gas to solids mass flow rate ratio. The numerical simulations indicate that the coarse particles move into the rope created in the elbow and secondary flows carry the small particles around the pipe circumference through the particle-free regions.