Particle‐level dynamics of clusters: Experiments in a gas‐fluidized bed

Particle-level dynamics of clusters: Experiments in a gas-fluidized bed

10.22541/au.162206659.93701850/v1 ◽

2021 ◽

Author(s):

Haifeng Wang ◽

Yanpei Chen ◽

Wei Wang

Keyword(s):

Energy Loss ◽

Fluidized Bed ◽

Particle Tracking ◽

Percolation Theory ◽

Cluster Size ◽

Particle Tracking Velocimetry ◽

Time Resolved ◽

Hydrodynamic Parameters ◽

Particle Level ◽

Large Clusters

The clustering is critical to understanding the multiscale behavior of fluidization. However, its time-resolved evolution on the particle level is seldom touched. Here, we explore both the time-averaged and time-resolved dynamics of clusters in a quasi-2D fluidized bed. Particle tracking velocimetry is adopted and then clusters are identified by using the Voronoi analysis. The time-averaged results show that the cluster hydrodynamic parameters depend highly on the cluster size and the distance from the wall. The number distribution of the cluster size follows a power law (~n)) of the percolation theory except for large clusters (n>100). The time-resolved analysis shows that the cluster coalescence can be simplified as a collision between two inelastic clusters, during which the net external force is roughly zero, and a snowplow model is proposed to predict its energy loss, ΔE ~ t. The cluster rupture is suggested to be caused by increasing torque.

Download Full-text

Motion and Temperature of Individual Particles in Two-Dimensional Fluidized Bed With Heat Transfer

ASME-JSME-KSME 2011 Joint Fluids Engineering Conference: Volume 1, Symposia – Parts A, B, C, and D ◽

10.1115/ajk2011-12023 ◽

2011 ◽

Author(s):

Takuya Miyauchi ◽

Satoshi Oh ◽

Takuya Tsuji ◽

Toshitsugu Tanaka

Keyword(s):

Heat Transfer ◽

Fluidized Bed ◽

Particle Tracking Velocimetry ◽

Fluidized Beds ◽

Numerical Models ◽

Simulation Models ◽

Two Dimensional ◽

Particle Level ◽

Heat Transfers ◽

Individual Particles

Fluidized beds are widely used in industrial processes concerned with heat transfer such as combustion, gasification, catalytic reaction and calcination. In recent years, numerical simulation models that predict the heat transfer phenomena in fluidized bed in the framework of DEM-CFD coupling simulation are developed. The heat transfer in fluidized beds is conducted by several mechanisms and its behavior is extremely complex. In order to improve these numerical models, it is important to know the relation between the convective and diffusive motion of particles and heat transfers in the particle-level. In the present study, a measurement technique based on the coupling between particle tracking velocimetry (PTV) and infrared thermography (IT) measurements is proposed. By using the technique, the motion and the temperature of individual particles and its relations with the characteristic flow structures formed in fluidized beds can be investigated simultaneously without disturbing the flow field. After careful preparations, the technique is applied to a two-dimensional gas-fluidized bed under a spouting condition and the motion and the temperature of individual particles largely-influenced by the bubble occurrences are clearly observed. The relations between convective and diffusive behaviors of individual particles and heat transfer in the bed are studied in detail.

Download Full-text

Insight on micro bubbling mechanism in a 2D fluidized bed with Group D particles

International Journal of Chemical Reactor Engineering ◽

10.1515/ijcre-2021-0070 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Fengguo Tian ◽

Shulei Liu ◽

Zifeng Zhao ◽

Ming Lei

Keyword(s):

Pressure Gradient ◽

Fluidized Bed ◽

Gradient Force ◽

Pressure Gradient Force ◽

Dem Simulations ◽

Driving Mechanisms ◽

Particle Level ◽

Gradient Forces ◽

External Forces ◽

Group D

Abstract By CFD-DEM simulations, the present work is aimed to investigate the transient gas-solid bubbling mechanisms along a whole bubble lifecycle in a 2D fluidized bed from a micro perspective. Systemic comparisons with CCD measurements confirm the validity of current simulations. Afterward, the manner of particle motion and its driving mechanisms at various stages are investigated. In order to do that, external forces are analyzed at an individual particle level, including the drag, pressure gradient force, and their resultant acceleration together with gravity. Many interesting findings have been achieved. For example, a switch in directions of drag and pressure gradient forces at the root of an initial bubble enables its detachment. And, regarding their contributions to the burst of a bubble, the drag force is several times of the pressure gradient forces. Present efforts help to offer a novel view of particle dynamics during the bubbling fluidization.

Download Full-text