Numerical investigation on the solid flow pattern in bubbling gas–solid fluidized beds: Effects of particle size and time averaging

Abstract

The effects of particle size on the solid flow pattern in gas–solid bubbling fluidized beds were investigated numerically using two-fluid model based on the kinetic theory of granular flow. In this regard, the set of governing equations was solved using finite volume method in two-dimensional Cartesian coordinate system. Glass bead particles with mean sizes of 880μm, 500μm, and 351μm were fluidized by air flow at excess gas velocities of 0.2m/s and 0.4m/s. For particle diameters of 880 and 351μm, the predicted characteristic times for solid dispersion were 0.14s and 0.15s, respectively, while characteristic times for solid diffusivity were 1.68ms and 0.75ms in the same order. Consequently, at identical time-sampling interval, for coarser particles, longer simulation time is required to achieve accurate solid flow pattern. Through examination of wide range of time-sampling interval from 0.1ms to 40ms, an optimum value of 10ms with minimum simulation time was obtained for coarser particles. The predicted solid flow patterns at a simulation time of 7s were in good agreement with the experimental data for both particle sizes of 880 and 351μm. In addition, it was demonstrated that the effects of particle size on the solid flow pattern should be investigated alongside the variations in the excess gas velocity. In detail, predicted solid flow pattern underwent significant change with the excess gas velocity in the bed filled with a small particle size of 351μm, but for larger particles no considerable change was seen. Moreover, the predicted gas bubble diameter and velocity were in agreement with experimental data.