Characteristics of particle velocity and concentration in a horizontal self-excited gas–solid two-phase pipe flow of using soft fins

Abstract

In order to reveal the mechanism of the low pressure drop at low air velocity in a horizontal excited gas–solid two-phase pipe flow of using soft fins, the distributions of particle velocity and concentration are measured by the high-speed particle image velocimetry (PIV) and image process. The test pipeline consists of a horizontal smooth acrylic tube with an inside diameter of 80mm and a length of about 5m. The polyethylene particles of density 978kg/m3 and 952kg/m3 with diameters of 2.3 and 3.3mm are used as test materials. The distributions of the time-averaged particle velocity and concentration are measured at the minimum air velocity and the solid mass flow rates of 0.45kg/s and 0.40kg/s in the acceleration and fully developed regimes. It is found that the particle concentration of using fins exhibits almost same profile as that of non-fin although the air velocities of using fins are lower than that of non-fin. In the acceleration regime, there is little difference of the normalized axial particle velocity up/Ua between short fins and non-fin. up/Ua of the long fins having low air velocity, however, is slightly higher than that of non-fin. In the fully developed regime, even though up/Ua of using long fins is obviously lower than that of other fins and non-fin in the lower part of pipeline, the steady gas–solid two-phase flow can be observed. It suggests that the long fins easily accelerate the particles and result in low pressure drop and low air velocity. For the relatively large particles, the effect of fins on up/Ua is smaller than that for the small particles. Due to the effect of fins’ oscillation, the vertical particle velocity decreases in the low part of pipeline, resulting in the particle dispersion and the reduction of particles–wall collision.