Flow characteristics of non-spherical wet particles in a draft tube spout-fluid bed
Most of the particles in industrial production have a non-spherical shape.However,the study of particle shape effect and liquid phase mechanism is insufficient,which is the main limiting factor for the application of draft tube spout-fluid bed in particle coating.In this study,the spherical and non-spherical cylindrical particles with similar particle size and density were selected as experimental materials.The pressure pulsation signal spectrum analysis and information entropy analysis of the two types of particles under different gas velocities and droplet introduction amounts were compared,and it is divided based on the gas-solid flow convection pattern in the bed.Meanwhile,the effect of particle shape and liquid phase under spouted-fluidized state were clarified by signal analysis method.The results show that non-spherical particles have a smaller minimum spouting velocity,multiple main frequency peaks and higher information entropy than spherical particles.These indicate that non-spherical particles have a high degree of chaos in the system.The solid circulation rate is reduced due to the friction and collision between particles in the draft tube.The minimum spouting velocity and the minimum spout fluidizing velocity are decrease owing to the introduction of liquid in the bed.Meanwhile,the liquid bridging force between particles is increased in the annular region,resulting in an increasing of the minimum fluidization velocity.However,the gas velocity is increased with the evaporating of liquid,resulting in a decrease in the minimum spouting velocity and the minimum spouting fluidization velocity.Due to the introduction of liquid during the spouted-fluidized flow pattern,the dominant frequency of pressure drop ΔpDT is reduced for the spherical particle.However,the dominant frequency of pressure drop ΔpDT is increased for the non-spherical particle.Moreover,owing to the liquid adhering,the spectrum analysis of non-spherical particles show a single dominant frequency peak with a larger amplitude.This indicates an enhanced regularity of pressure fluctuations for non-spherical wet particles.
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