Multi-scale motion characteristics of coarse particles in a swirling flow pneumatic conveying system with the discrete wavelet transform

In order to achieve low-speed operation of pneumatic conveying, this paper proposes a new type of swirling flow blade that promotes particle suspension and acceleration by controlling the generation of swirling. Firstly, the energy-saving efficiency of swirling flow was evaluated in term of the pressure drop and power consumption coefficient, and it is revealed that the optimal conveying velocity and power consumption coefficient are reduced for the swirling flow compared to the conventional axial flow, the maximum reduction rates are 12.99 % and 9.47 %, respectively. Then, to master the particle motion characteristics for swirling flow conveying, the 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 swirling flow is lower than the conventional axial flow around the bottom of the pipe, and the particle velocity of swirling flow is higher than the conventional axial flow, suggesting that the particles are easily suspended and accelerated for the swirling flow conveying. The core innovation lies in the analysis of the particle velocity field by utilizing one-dimensional discrete wavelet transform (DWT) and continuous wavelet transform (CWT), which reveals the energy-saving mechanism of swirling flow conveying. The results show that using blade enhances large-scale velocity fluctuations and particle suspension, leading to lower center frequencies. It also increases pulsation intensity at pipe bottom, stabilizes small-scale motion at pipe top, and improves spatial correlation.