Comprehensive investigations on flow field in liquid-solid mini-fluidized beds

The Particle Image Velocimetry (PIV) technology was adopted to study the expansion ratio, solid holdup, minimum fluidization velocity, velocity field, turbulent kinetic energy, vortex structure and particle velocity of liquid-solid mini-fluidized beds with bed diameter of 1–3 mm. Due to the wall effect caused by the decrease of bed diameter, the axial velocity at the central axis was 1.68–1.93 times of that near the wall. Both liquid and particle phases had tendency to move toward the central axis of bed. When the liquid velocity gradually increased, the turbulence phenomenon appeared in the liquid-solid mini-fluidized bed. Regarding particles, their axial velocity was mainly influenced by the superficial liquid velocity, while the radial velocity was predominantly by vortices and friction between particles. In this study, the overall movement of flow field was comprehensively obtained, which provided a certain theoretical reference for the design of the liquid-solid mini-fluidized bed reactors. [Display omitted] •Particle fluidization and flow field characteristics were obtained by PIV method.•New Richardson-Zaki empirical equation constants (n and k) were determined.•Effects of experimental conditions on flow field characteristics were investigated.•Turbulence was found in the liquid-solid mini-fluidized beds.•The contributing factors of particle axial and radial velocity were discussed.