Swirling air fluidized beds for microgravity applications

In collaboration with Anjani Didwania (AMES, UCSD) & Lev S. Tsimring (INLS, UCSD)
 
 

A swirling fluidized bed (SFB) is a bed of rigid particles contained by a cylindrical distributor plate that is rotating rapidly about its axis. The particulate material forms an annular layer at the circumference due to the large centrifugal forces produced by rotation of the bed. The fluid is injected inward through the porous cylindrical wall. The wall distributor allows the fluidizing fluid to flow uniformly into the bed. Unlike gravitationally fluidized beds, the body force in a centrifugal bed becomes a controllable parameter determined by the rotation speed and the bed radius. Thus the minimum fluidization velocity can in principle be fixed at any rate by changing the rotating speed of the bed.

SFBs appear as strong candidates for many microgravity applications (e. g. solids waste processing) due to their excellent fluid-solid contacting characteristics and low equivalent system mass (ESM) in terms of compactness (low volume), low overall mass and high reliability.

However, unlike the gravitationally fluidized beds, the mechanics of fluid-solid interaction in SFB has not been investigated even in the context of terrestrial applications. The project is aimed at a thorough experimental and theoretical investigation of the mechanics and particle-phase circulation patterns in a swirling fluidized bed.
 

Figure:A snapshot of a 3D simulation of $2\cdot 10^4$ particles in a shallow air fluidized bed near the fluidization threshold. The particles are color-coded according to their instantaneous velocity, indicating the granular temperature across the bed.

The experimental work will be be done under supervision of Dr. Anjani Didwania (AMES, UCSD). It is intended to examine the various flow regimes and their stability in a SFB by making voidage and particle phase velocity fluctuation measurements and visualizations. The effect of various operating and physical parameters will be investigated with special emphasis on the role of gravitational forces on the particle phase circulation in these beds.

The theoretical work to be done will involve two complementing approaches: stability analysis of the state of fluidization to three-dimensional disturbances using conventional continuum models [19,20,21] and extensive 3D molecular dynamics simulations.

During the last year of collaboration with Lev S. Tsimring and Igor S.  Aranson I have developed and implemented an efficient parallel algorithm for simulations of soft particles in two and three dimensions. The code has been applied to the study of partially fluidized shear granular flows [22],[12]. A modification of this code which accounts for the air flow is now being used to study oscillations in a shallow fluidized bed (see Figure 4, [23]).

The proposed experimental, analytical, and computational work should mark the beginning of a systematic study of mechanics and particle-phase circulation in SFBs, which are expected to play an increasingly crucial role in many fluid-solid contacting processes under microgravity conditions.