Experimental exploration of particle cluster characteristics in the gas-solid diameter-varying fluidized bed

Particle cluster motions play a significant role in the gas-solid suspension flow. In this work, systematical experiments were carried out to deeply reveal the complex mechanisms of cluster motion in the diameter-varying riser. Based on the instantaneous solid concentration fluctuations, cluster dynamic parameters characterizing cluster motions were obtained and analyzed. Compared to the traditional riser, cluster parameters tend to show a clear monotonic change with operating conditions in the diameter-varying riser. Cluster dynamic parameters increase along the radial direction but decrease with the height of the bed. Additionally, cluster motion is more affected by operating conditions and spatial placements near the wall region than in the center region. A comparison between the enlarged and the straight segments shows that cluster motion intensifies in the enlarged section under the texted conditions. Finally, an improved cluster holdup model, appropriate for the diameter-varying riser, was developed. The differences of particle cluster characteristics emerge due to the variation of riser geometrics. For instance, cluster holdup distributions change with bed height, resulting in a discrepancy of traditional prediction model. An improved model of cluster holdup was established to predict cluster holdup in the diameter-varying riser, based on the obtained experimental data. [Display omitted] •The dominance of cluster motions increases in the enlarged section.•Cluster motions weaken along the axial direction.•Cluster motions exhibit sensitivity near the wall region than the center.•A new prediction model on cluster holdup is developed.