Wavelet multi-scale analysis on particle dynamic characteristics of the vertical tubes in a horizontal-vertical pneumatic conveying system

Abstract

To study the flow characteristics of particles in the vertical tube, the velocity is measured at the minimum pressure drop (MPD) by using a high-speed particle image velocimeter (PIV). Firstly, the pneumatic conveying system’s pressure drop and the particle velocity characteristics in the vertical tube were investigated. Then, for the axial fluctuation velocity of the particles, the continuous wavelet transform, and one-dimensional discrete orthogonal wavelet decomposition are used to reveal the dynamic characteristics of the particles based on the time-frequency characteristics, the contribution of wavelet levels to the energy of particle fluctuations, the auto-correlation of each wavelet level and the probability distribution of wavelet levels. The results demonstrate that large-scale movement dominates particle movement in the vertical tube, whereas small-scale movement increases as conveying height rises. The energy contribution of the low-frequency wavelet level is larger, and this contribution decreases with the acceleration of the particles along the tube. The high-frequency wavelet level’s auto-correlation coefficients decay more slowly and have a longer duration. At increasing wavelet levels, the skewness and kurtosis coefficients grow, and the departure of the Gaussian probability distribution becomes more obvious.