Profiles of particle velocity and solids fraction in a high-density riser

Abstract

Radial profiles of particle velocity and solids fraction in a high density circulating fluidized bed (HDCFB) at average cross-sectional solids fraction up to 0.21 were measured by an improved optical fiber laser doppler velocimeter and an optical fiber density sensor. The axial development of these radial profiles and the influence of operating conditions on the profiles were examined. The results showed that similar radial profiles of solids fraction exist in the HDCFB. The following Boltzman function can correlate well the solids fraction profile: (1 − ɛ)/(1 − ɛ) = 2.2 − (2)/(1 + exp(10· r/ R −7.665)). The radial profiles of particle velocity in HDCFB can also be described by the Boltzman function, that is, ( V p)/ ( U g) = (2.7)/(1 + exp(10· r/ R −10· X o) − 0.2). The Boltzman profiles of particle velocity in the high density operating regime was different with the parabolic shape operating in dilute phase regime. The local particle fluctuation velocity in the center of the riser increases with average solids concentration, while the fluctuation velocity decreases sharply as the radial position near the wall.