Liquid-fluidized beds in narrow pipes: dynamics and instabilities

Abstract

A fluidized bed is a suspension of solid particles (grains) in a vertical tube submitted to an ascendant fluid flow. Given their high heat and mass transfers, fluidized beds are frequently employed for the gasification of solid fuels. Uniform fluidized beds are uncommon in industrial facilities, and usually instabilities appear. These instabilities consist of transverse waves, bubbles, or long bubbles. For liquid-fluidized beds in narrow tubes, the dynamics and instabilities of the beds are not completely understood, and the problem is still open. This project proposes analytical and experimental studies of the grain dynamics and bed instabilities for this specific case. The analytical part will employ some methods of applied mathematics in order to obtain expressions for the growth rates, wavelengths, frequencies, and celerities of instabilities. The experiments will consist of fluidized beds in different tubes, where the individual motion of grains will be filmed with a high-speed camera, the instabilities will be filmed with a high-definition camera, and the fluid flow will be measured with PIV (Particle Image Velocimetry). Numerical codes will be developed to post-process the images. The objectives are to get a better knowledge of the problem, and to obtain expressions for the grains displacements and for the main characteristics of instabilities (growth rates, wavelengths, and celerities).