Presently, many industrial processes use pneumatic conveying systems to transport granular materials. Practically, different conveying regimes such as dilute- and dense- phase conveying are normally used. The dilute phase conveyance is usually operated at high conveying velocity, leading to high pressure drop, pipe erosion, and particle degradation. As for the dense phase conveyance, low conveying velocity usually results in unstable flow, which causes vibration and blockage of the conveying pipe. Therefore, a key design criterion of pneumatic conveying system is to keep the conveying velocity as low as possible to minimize the pressure drop without blockage occurring. Consequently, to resolve this shortcoming, it is imperative that the particle dynamics of pneumatic conveying system, especially the particle dynamics in the range of relatively low conveying velocity, be investigated. In addition, little attention has been paid to the particle fluctuation velocity fields in both fully-developed and acceleration regimes from multi-scale point of view, which would provide more detailed information on the particle dynamics in the gas–solid two-phase pneumatic conveying system.
To this note, Dr. Yan Zheng at Jiangsu University of Technology and Professor Akira Rinoshika at Yamagata University undertook continuous and one-dimensional orthogonal wavelet analyses so as to reveal the multi-scale particle dynamics in the acceleration- and fully-developed regimes. Their work is currently published in the research journal, Advanced Powder Technology.
In brief, the research method employed commenced with an in-depth assessment of the time frequency characteristics of axial particle fluctuation velocities using continuous wavelet transform. Next, the particle fluctuation velocities were decomposed into different wavelet levels based on their central frequencies. Eventually, the fluctuation velocities of different wavelet levels were analyzed in terms of particle fluctuation energy, two-point correlation and probability distribution.
The time frequency characteristics of particle fluctuation velocity were seen to indicate that the small-scale particle motions were suppressed and tend to transfer into large scale particle motions from acceleration regime to fully developed regime. Additionally, near bottom part of pipe, the fluctuation energy of axial particle motion was mainly contributed from the wavelet levels of relatively low frequency, however, near the top part of the pipe wavelet levels of relatively high frequency were observed to make comparable contribution to the axial particle fluctuation energy in the suspension flow regime. This led the researchers to deduce that the latter contribution declined as the particles became more accelerated along the pipe.
In summary, Prof. Akira Rinoshika and Dr. Yan Zheng demonstrated the successful application of continuous wavelet transform and one-dimensional orthogonal wavelet decomposition in analyzing particle fluctuation velocity measured by the high-speed particle image velocimetry (PIV) in a horizontal gas-solid two-phase flow. It was seen that the low frequency wavelet levels exhibited large spatial correlation, and this spatial correlation increased as the particles flowed from acceleration regime to fully developed regime. Altogether, the skewness factor and kurtosis factor of wavelet level suggest that the deviation of Gaussian probability distribution is associated with the central frequency of wavelet level, and the deviation from Gaussian distribution is more evident as increasing central frequency. The higher wavelet levels can be linked to small scale particle motions, which lead to irregular particle fluctuation velocity.
Yan Zheng, Akira Rinoshika. Wavelet multi-resolution analysis on particle dynamics in a horizontal pneumatic conveying. Advanced Powder Technology, volume 29 (2018) page 2404–2415.Go To Advanced Powder Technology