Wall roughness effects on pneumatic conveying of spherical particles in a narrow horizontal channel

Abstract

The present study is related to an experimental analysis of the particle behaviour in a narrow horizontal channel flow (length=6 m, height=35 mm, the length is about 170 channel heights) for different degrees of wall roughness in the range between 2 and 17 μm. Simultaneous air and particle velocity measurements were realised by using a two-component phase Doppler anemometry (PDA), and the static pressure along the channel was obtained using thin-film pressure sensors. The particles were spherical glass beads with mean diameters in the range of 60–625 μm. The presented results are restricted to an average conveying velocity of about 20 m/s, and the particle mass loading could reach values of about 2 (the mass loading is defined as the ratio of particle to gas phase mass flow rates), depending on particle size. The results demonstrate the influence of particle size, mass loading and the degree of wall roughness on the particle concentration and velocity profiles in the developed gas-particle flow. Additionally, these data allowed to estimate averaged properties, such as the particle slip velocity, their fluctuation energy, as well as the mean free paths between subsequent wall and interparticle collisions. Wall roughness increases the particle fluctuating energy. Thereby, the wall collision and the interparticle collision mean free paths are reduced. The increasing wall collision frequency with increasing degree of wall roughness results in a higher momentum loss for the particle phase, and hence, the slip velocity as well as the pressure loss also increase remarkably.