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

• Published in: Powder technology Vol. 304; pp. 55 - 62
• Main Authors: do Nascimento, Orlando L., Reay, David A., Zivkovic, Vladimir
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.12.2016; Elsevier BV
• Subjects: Adhesion; Fluid dynamics; Fluid flow; Fluidization; Fluidized bed reactors; Fluidized beds; Gravitation; Gravity; Heat transfer; Hydrodynamics; Low Reynolds number; Micro-fluidized bed; Microfluidics; Process intensification; Surface forces; Velocity; Wall effects; Process intensification; Fluidization; Wall effects; Micro-fluidized bed; Surface forces; Microfluidics
• ISSN: 0032-5910; 1873-328X
• DOI: 10.1016/j.powtec.2016.05.013

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 acid-base theory of van Oss, Chaudhury and Good combined with the Derjaguin approximation to estimate the wall adhesion forces for comparison 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. [Display omitted] •Study of fluidization of glass and PMMA particles in micro-fluidized PMMA beds•Different sized beads were used for each material to vary adhesion-drag force ratio.•Experiments performed in 1 and 4mm2 micro-beds to study methodically wall effects•The incipient fluidization is postponed due to adhesion forces and wall effects.•The increase in Umf linearly scales to product of force and particle-bed ratios.