Studies on the local flow characteristics and flow regime transitions in a square fluidized bed

Abstract

Flow patterns seen in a fluidized bed of square cross-section during the transition from bubbling to turbulent fluidization were studied with differential pressure data and optical fiber probe signals. The transition velocity to turbulent flow regime (Uc), based on differential pressure analysis varies with measurement locations. Spatial distributions of the dilute and dense phases were illustrated by contour maps of the time averaged solids holdup (εs) and standard deviation (σs). A clear correlation between σs and εs of the local solids holdup signals was found and developed using a bimodal distribution analysis. Based on that, the relationship between local fluctuations and global regime transition was proposed. The transition to the turbulent regime is identified to the proportion of the σs = 0.16 contour line enclosure reaching higher than 0.5. A new regime map is proposed to identify the bubbling, turbulent and fast fluidization regimes and to delineate the regime transitions in terms of the relationship between εs and σs.