Bubble dynamics in a 3-D gas-solid fluidized bed using ultrafast electron beam X-ray tomography and two-fluid model

Bubble characteristics in a three-dimension gas-fluidized bed (FB) have been measured using noninvasive ultrafast electron beam X-ray tomography. The measurements are compared with predictions by a two-fluid model (TFM) based on kinetic theory of granular flow. The effect of bed material (glass, alumina, and low linear density polyethylene (LLDPE), dp ~1 mm), inlet gas velocity, and initial particle bed height on the bubble behavior is investigated in a cylindrical column of 0.1-m diameter. The bubble rise velocity is determined by cross correlation of images from dual horizontal planes. The bubble characteristics depend highly upon the particle collisional properties. The bubble sizes obtained from experiments and simulations show good agreement. The LLDPE particles show high gas hold-up and higher bubble rise velocity than predicted on basis of literature correlations. The bed expansion is relatively high for LLDPE particles. The X-ray tomography and TFM results provide in-depth understanding of bubble behavior in FBs containing different granular material types