Study of Transitional Velocities of Solid-Liquid Micro-circulating Fluidized Beds by Visual Observation

Solid-liquid micro-fluidized beds (FBs), i.e., fluidization of micro-particles in sub-centimetre beds, hold promise in applications in the micro fluidics and micro-process technology context. This is mainly due to fluidized particles providing enhancement of mixing, mass and heat transfer under the low Reynolds number flows that dominate in micro-devices. Although there are quite few studies of solid-liquid micro-fluidized beds, we are presenting the first study of a micro-circulating fluidized bed. The present experimental research was performed in a micro-circulating fluidized bed which was made by micro-machining channels of 1 mm(2) cross section in Perspex. PMMA and soda lime glass micro-particles were used as the fluidized particles and tap water as the fluidizing liquid to study flow regime transition for this micro-circulating fluidized bed. The results are in line with the macroscopic observation that the critical transition velocity from fluidization to circulating regime is very dependent on solid inventory, but once the inventory is high enough it is approximately equal to the particle terminal velocity. However, the transitional velocity is weakly dependent on wall effect and surface forces conforming the importance of these two properties in a micro-fluidized bed system. Similarly, the transitional velocity to transporting regime is a strong function of surface forces. Finally, combining these results with our previous result on conventional fluidization the map of solid-liquid fluidization in a micro-circulating fluidized bed system is constructed showing conventional fluidization, circulating fluidization and a transport regime.