Solid-liquid fluidized beds: fluid flow, grain dynamics and pattern formation

Abstract

A fluidized bed is basically a suspension of granular matter by an ascending fluid flow in a vertical tube. Given their high heat and mass transfers, fluidized beds are frequently employed in industry, in processes such as combustion of coal and coating of solids. They are also used for particle classification and separation, such as happens in water treatment and chemical processes. Uniform fluidized beds are rarely encountered in industrial applications and instabilities, such as transverse waves, bubbles and long bubbles, usually appear. In addition, in polydisperse beds segregation and stratification are common. This project consists of experimental and numerical investigations of the dynamics of grains, bed instabilities, and fluid flow behavior. Experiments will be performed in solid-liquid fluidized beds in transparent tubes. The fluid flow will be measured with both a low-frequency (4 Hz) PIV (Particle Image Velocimetry) and a high-speed camera (1 kHz) together with a continuum laser, and we will employ the index matching technique between the granular material and the liquid. For the granular material, the motion of grains will be recorded with a high-speed camera and, afterwards, images will be processed with in-house numerical codes. Simulations will be performed by using CFD-DEM (Computational Fluid Dynamics - Discrete Element Method). The open-source codes OpenFOAM (CFD part) and LIGGGHTS (DEM part) will be used. From the experiments and numerical results, we expect to obtain the structure of the fluid flow within a fluidized bed (mean flow, second order moments, etc.), the trajectories of individual grains, and to identify the fluid-grain, grain-grain and grain wall momentum transfers. (AU)