Effects of airflow velocity and inlet airflow angle on binary particle mixing in a rotary drum fluidized bed

In rotary drum fluidized beds, the mixing efficiency of binary particles is governed by the coupled interaction between mechanical motion and gas–solid flow, yet the combined effects of airflow velocity, inlet airflow angle, drum rotation speed, and baffle height remain insufficiently understood. To address this issue, this study employs a two-way coupled CFD–DEM approach to examine how airflow and mechanical parameters influence particle mixing, using the Lacey mixing index to quantify uniformity. The results show that airflow velocity plays a dominant role: with h = 15 mm and ω = 60 rpm, a 5 m·s⁻¹ inlet airflow reduces the mixing time from 4.0 s to 2.5 s, whereas 6 m·s⁻¹ induces size-dependent stratification. The inlet airflow angle further regulates the mixing rate, with 75°–90° yielding the fastest mixing. Rotation speed controls cascading intensity, where moderate speeds (30–45 rpm) ensure stable mixing, while 75 rpm causes centrifugal segregation. Baffle height exhibits a clear optimum: 15–25 mm enhances early mixing, whereas 50 mm reduces efficiency. Gas–solid coupling decreases the mean contact force by 64.7% and slightly increases collision power. These findings provide mechanistic insight for optimizing airflow-assisted mixing in rotary drums.