Motion Characteristics of Coarse Particles in the Horizontal–Vertical Pneumatic Conveying System with Swirling Flow

In order to achieve low-velocity operation of the pneumatic conveying system, a novel swirling flow blade device is proposed that facilitates particle suspension and acceleration through controlled vortex generation. First, the energy-saving efficiency of swirling flow was evaluated in terms of the pressure drop, additional pressure drop coefficient, and power consumption coefficient, and it is revealed that the optimal conveying velocity and coefficient of power consumption are reduced for the swirling flow compared to the conventional axial flow; the maximum reduction rates are 14.4% and 14.6%, respectively. Then, to master the particle motion characteristics for swirling flow conveying, electrical capacitance tomography (ECT) and particle image velocimetry (PIV) were employed to analyze the particle concentration and velocity distributions; the results show that the particle concentration of the swirling flow is lower than the conventional axial flow around the bottom of the pipe, and the particle velocity of the swirling flow is higher than the conventional axial flow, suggesting that the particles are easily suspended and accelerated for the swirling flow conveying. Furthermore, the particle fluctuation velocity is analyzed by using proper orthogonal decomposition (POD) and continuous wavelet transform (CWT) to reveal the energy-saving mechanism of swirling flow conveying. It is found that the swirling flow enhances the energy contribution of Modes 1 and 2 compared to the conventional axial flow. In addition, the presence of swirling flow reduces the dominant frequency of particle motion and increases the large-scale motion of particles.