Gas–solid flow behavior in a horizontal pipe after a 90° vertical-to-horizontal elbow

Abstract The characteristics of the particle flow in a horizontal pipe following a 90° vertical-to-horizontal elbow were investigated both numerically and experimentally. Laboratory experiments were conducted in a 0.154 m ID test section. The effects of air velocity, the ratio of air-to-solids mass flow rate, geometry of the elbow and inlet conditions on gas–solid flow patterns were investigated experimentally. Pulverized coal with a mean particle diameter of 50 μm was used as the solid material. Experiments were performed with conveying air velocities ranging from 15 to 30 m/s and air-to-solids mass flow rate ratios of 1 and 3, with elbows having bend radius to pipe diameter ratios of 1.5 and 3. Measurements of particle concentration and particle velocity were performed at various locations along the horizontal pipe using a fiber-optic probe which was traversed over the pipe cross-section of the pipe. It was observed that the strong rope created by the elbow disintegrates within an axial distance of 10 pipe diameters. Fully developed concentration and velocity profiles were obtained within approximately 30 pipe diameters from the elbow exit plane. The rope behavior was different for the two elbows studied ( R / D =1.5 and 3). The shapes of the fully developed profiles were found to be independent of inlet conditions. CFD simulations of gas–solid flow through 90° circular elbows were performed using the Lagrangian approach. The simulations were used to predict the location of the rope and its dispersion rate along the horizontal pipe after the elbow exit plane.