Direct resolution of differential pressure fluctuations to characterize multi-scale dynamics in a gas fluidized bed

摘要

A direct resolution approach was proposed to decompose differential pressure signals from a gas fluidized bed into macro- and super-imposing components, which were further subjected to structure density function analysis (SDF analysis) to study dynamics of multi-scale structures in flow. Direct resolution performed well in extracting feature information of multi-scale structures, especially macro- and meso-scale structures whose dynamic behaviors majorly affected hydrodynamics in bed, from measured differential pressure fluctuations. With the assistance of Gaussian fitting and Kolmogorov-Smirnov test, SDF analysis divided the probability distribution of multiple structures with respect to their amplitude scale r into four feature regions (Regions B-I, B-II, B-III and Region A). Parameter K-SDF derived from slope of Region B-II quantified frequency of various meso-scale structures in flow, and well followed the tendency of flow patterns transition after being normalized by bubble (slug) rising velocity U-b(sl). Frequency of macro scale structures in slugging flow depended greatly on rising velocity of slugs, so SDFmacro increased with increased fluidization velocity. Developed turbulent flow had a high SDFmacro exceeded 0.8 Hz due to the fast passage and split/integration of large voids. Structures localized in Region A mainly represented noise from measurements, other measurable micro-scale disturbances in single phases or phase-interfaces, and had an occurring frequency increased with increase of fluidization velocity. (C) 2016 Elsevier Ltd. All rights reserved.