On importance of surface forces in a microfluidic fluidized bed

Abstract

Fluidized beds potentially offer a means of significantly enhancing mixing, heat and mass transfer under the low Reynolds number flow conditions that prevail in microfluidic devices. However, as surface forces at the microscale can be significant relative to hydrodynamics forces, fluidization within a microfluidic channel can be potentially hindered or even prevented through particle adhesion to the channel walls.We have used the acid-base theory of van Oss, Chaudhury and Good to predict the propensity for adhesion of particles on microfluidic fluidized bed walls for various practically important wall material/particle/fluid combinations. Comparison of the results from this approach with experimental observations indicates it provides a robust means of predicting the adhesion propensity. It is also demonstrated how results from the model can be used to estimate for a system of interest the particle size range in which the particle-wall surface forces transition from being dominate to being insignificant.

Experimental study of efficient mixing in a micro-fluidized bed

“…Results and Discussion Figure 3 shows images of the bed expansion at steady state under different inlet volumetric flow rates. The overall behaviour of the bed matched that described in our previous reports [28,29]. As predicted [29], ethanol proved to be a good fluidising medium for the glass particle/PDMS microchannel system used here, with smooth and stable homogenous fluidization.…”

“…This makes particle aggregation and adhesion to the bed wall a potential issue, even to the point of preventing fluidization [28,29]. The acid-base model of van Oss, Chaudhury and Good combined with the Derjaguin approximation can be used to predict wall material/particle/fluid triplets that avoid this issue [29,38,39]. In the case of the wall material/particle pair considered here, we have both predicted and demonstrated [29] that ethanol is a suitable fluidizing medium, hence why it has been used in the work reported here.…”

“…Since its initial introduction by Potic et al [33], only a small number of studies have been reported on liquid fluidization in µFB. Whilst some of these studies have been application-focused [34,35], the vast majority have focused on hydrodynamic aspects of µFBs [28,31,36,37] and the effects of surface forces and wall effects on their fluidization behaviour [28,29,38,39]. Of these, only Doroodchi et al [31] have focused in detail on mixing.…”

“…The micro-fluidized bed (µFB) [28,29], which is essentially fluidization of micron-sized particles in channels of sub-centimetre cross-section, can provide enhancement of mixing, mass and heat transfer for micro-devices due to the chaotic motion of the fluidized particles [30][31][32]. Since its initial introduction by Potic et al [33], only a small number of studies have been reported on liquid fluidization in µFB.…”

A new method for reconstruction of the structure of micro-packed beds of spherical particles from desktop X-ray microtomography images. Part B. Structure refinement and analysis

“…Structural change during an RMC-SA simulation the RMC-SA algorithm is not entirely effective in removing non-physical occurrences, they were largely observed to occur near the wall, suggesting that surface forces between the particles and the capillary wall may be playing a role, something that has been observed in other systems, including micro-channels [17], porous media [18] and micro-fluidized beds that fail to fluidize due to the surface forces being more significant than the prevailing hydrodynamic forces [19,20]. Comparison between the starting model (i.e.…”