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

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 (U_c), 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 (ε_s) and standard deviation (σ_s). A clear correlation between σ_s and ε_s 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 σ_s = 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 ε_s and σ_s.