Influence of surface forces and wall effects on the minimum fluidization velocity of liquid-solid micro-fluidized beds

Micro-fluidized beds represent a novel means of significantly enhancing mixing, mass and heat transfer under the low Reynolds number flows that dominate in micro-devices used in microfluidics and chemical micro-process technologies. This is one way of implementing process intensification. Major differences of micro-fluidized beds from their classical macro-scale counterparts are the critical importance of surface forces and almost unavoidable wall effects due to their small bed size. Surface forces can become dominant over gravity and hydrodynamics forces at the microscale and fluidization could either be hindered or even prevented through the adhesion of particles to the walls of the bed. We have used the add-base theory of van Oss, Chaudhury and Good combined with the Derjaguin approximation to estimate the wall adhesion forces for compadson with hydrodynamics forces. Our new experiments show interesting fluidization behaviour at the boundary of micro-flow as a result of interplay between the ratio of surface and hydrodynamics forces and wall effects which both influence the minimum fluidization velocity. (C) 2016 Elsevier B.V. All rights reserved.