Characterization of the cross-sectional particle concentration distribution in pneumatic conveying systems

Abstract

The development of the cross-sectional distribution of the concentration of fine powders in dilute phase pneumatic conveying through different pipe elements was examined in detail in order to characterize the degree of segregation. The pipe system considered involved horizontal and vertical pipes connected by pipe bends of different bend radii. Additionally, it was possible to change the configuration into a combination of horizontal pipe, pipe bend, and horizontal pipe. Measurements were performed using smooth glass pipes and stainless steel pipes with a known degree of roughness. The average conveying velocity was varied between 10 and 30 m/s, and particle mass loadings between 0.2 and 1.0 (kg dust/kg air) were considered. The particles used in the study were spherical glass beads with a number mean diameter of 40 μm. The laser-light sheet method combined with digital image processing was applied to characterize the degree of non-uniformity of the particle concentration distribution in the different pipe elements. With the light sheet intersecting the pipe cross-section at an angle of about 45°, it was possible to obtain an entire field picture of the intensity of the light scattered by the particles. Using a simplified theory, the power of the scattered light could be related to the particle concentration distribution in the cross-section of different pipe elements (e.g. horizontal and vertical pipes). Additionally, information on the particle velocity and the spatial development of the particle size distribution were obtained by phase-Doppler anemometry (PDA) which allowed single point measurements along a line through the pipe cross-section. Moreover, accurate particle concentration measurements were performed by PDA with a recently developed method. The results revealed the influence of the different flow conditions, i.e. conveying velocity and particle mass loading, on the cross-sectional distribution of the particle concentration in different pipe elements. It was furthermore found that the wall roughness has a considerable influence on the development of the particle concentration distribution.