Magnetic Field Assisted Fluidization - A Unified Approach Part 7. Mass Transfer: Chemical reactors, basic studies and practical implementations thereof

In order to study the settling mechanism of particles in an air–solid magnetically stabilized fluidized bed (MSFB) for separation, we carried out free settling and quasi-zero settling tests on the tracing particles. The results show that the main resistance forces as the tracing particles settled in an air–solid MSFB were motion resistance force and yield force. The motion resistance and yield forces greatly hindered the free settling of the particles by greatly decreasing the acceleration for settling process of the particles. The acceleration decreased from 3022.62 cm/s 2 to zero in 0.1 s, and in the end, the particles stopped in the air–solid MSFB. The yield force on particles increased with increasing the magnetic field intensity, resulting in decrease of the quasi-zero settling displacement. However, the yield force on particles decreased with increasing the fluidized air velocity, leading to increase of the quasi-zero settling displacement. When the structure and operating parameters of the air–solid MSFB were set up, the yield stress on particles stopped in an air–solid MSFB was a function of diameter and density of particles. The settling displacements of equal diameter particles increased with increasing their densities, and the settling displacements of equal density particles increased with increasing their diameters.

Motion behavior of particles in air–solid magnetically stabilized fluidized beds for separation

MAGNETIC FIELD ASSISTED FLUIDIZATION – A UNIFIED APPROACH Part 6. Topics of Gas-Liquid-Solid Fluidized Bed Hydrodynamics

Various approaches to structure gas-solid fluidized beds are reviewed, followed by detailed discussion on the use of gas pulsation to induce dynamic structuring. Granular media are dissipative systems, which develop complex spatiotemporal patterns when excited by an oscillating energy source. Here, we discuss how such perturbations initiate surface patterns and how these could propagate into a macroscopically organized flow. We call this dynamically structured fluidization. Vibrated shallow granular layers form ordered surface waves. The hydrodynamics of pulsed gas-fluidized layers are related, but more complex: Under appropriate conditions, surface waves transition into a three-dimensionally ordered bubbling flow. This occurs in much deeper granular beds than under vibration, indicating distinct physics. In this dynamically structured state, bubbles organize into a scalable sub-harmonic, triangular lattice that is highly predictable and responsive to changes in oscillation parameters, allowing for an unprecedented level of control. Structured bubbling is observed only under sufficiently dense conditions; thus, a dynamically structured fluidized bed sits between fixed and fluidized beds, offering opportunities for process intensification, due to less macromixing than traditional fluidization, but a higher level of control through micromixing. This informs new intensified designs for processes that are highly exothermic, involve particle formation, thermally sensitive or high-value materials.

Xiaofang Li

Papers

L–S mass transfer in G–L–S countercurrent magnetically stabilized bed with amorphous alloy SRNA-4 catalyst

Local heat transfer properties in co- and counter-current G–L–S magnetically stabilized fluidized beds