CHARACTERIZATION OF THE CROSS-SECTIONAL PARTICLE CONCENTRATION DISTRIBUTION IN PNEUMATIC CONVEYING SYSTEMS

The development of the cross-sectional distribution of the concentrati on of fine powders in dilute phase pneumatic conveying through differe nt pipe elements was examined in detail in order to characterize the d egree of segregation. The pipe system considered involved horizontal a nd vertical pipes connected by pipe bends of different bend radii. Add itionally, it was possible to change the configuration into a combinat ion of horizontal pipe, pipe bend, and horizontal pipe. Measurements w ere 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 wer e spherical glass beads with a number mean diameter of 40 mum. The las er-light sheet method combined with digital image processing was appli ed to characterize the degree of non-uniformity of the particle concen tration distribution in the different pipe elements. With the light sh eet intersecting the pipe cross-section at an angle of about 45-degree s, it was possible to obtain an entire field picture of the intensity of the light scattered by the particles. Using a simplified theory, th e power of the scattered light could be related to the particle concen tration 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 dis tribution were obtained by phase-Doppler anemometry (PDA) which allowe d single point measurements along a line through the pipe cross-sectio n. Moreover, accurate particle concentration measurements were perform ed by PDA with a recently developed method. The results revealed the i nfluence of the different flow conditions, i.e. conveying velocity and particle mass loading, on the cross-sectional distribution of the par ticle concentration in different pipe elements. It was furthermore fou nd that the wall roughness has a considerable influence on the develop ment of the particle concentration distribution.