(513d) Fractionation of Suspensions of Elongated Particles in a Channel: Influence of Particle Concentration and Reynolds Number

Hydrodynamic fractionation describes a size, and/or shape based particle separation process in channel flow by a side-channel or slotted channel wall. Wall-bounded fluid is removed via the side channels due to reduced pressure in the side channels. Particles entrained in the side channel flow are removed from the main flow. Separation performance depends on a multitude of parameters including upstream flow conditions, slot geometry, and particle size and shape. The influence of the parameter are investigated for analytical and industrial applications ranging from the separation of different types of human and bacterial cells (Sugaya, et.al., Biomicrofludics, 5, 2011, 024103:1-13) to the separation of fibers (Dong, et.al., Tappi Journal, 4, 2004, 3-7 ).

Reported studies however are limited to dilute particle flow without particle-particle interaction. At increased particle concentration, (i) particles collide, and (ii) might form clusters. An extreme example is the formation of flocs for fibrous, i.e. long aspect ratio particles (Kerekes, Nordic Pulp and Paper Research Journal, 21, 2006, 598-612). Single particle motion is highly restricted and particles move as a bulk.

In this talk we will present results from a recent investigation of the separation of elongated particles at higher concentration. The main channel is constructed from Plexiglas to allow image analysis of the flow conditions. The separation channel is constructed by additive manufacturing to allow sophisticated geometry. Flocculation and thus the formation of a strong network was achieved by using flexible elongated particles. The particle concentration and the Reynolds number and thus the strength of the particle network had been varied in the experimental investigation.

Specifically we will present the (i) upstream condition of the particle network and (ii) and the motion of single particles at the separation slot, and (iii) link it to the measured grade efficiency, i.e. the fraction of particles per length remaining in the main channel. The results show the dependence of the separation performance on the network strength. With increasing Reynolds number, the number of separated particles per particle length increased and thus the grade efficiency decreased.

Acknowledgement
JDRP, JK, and SR acknowledge funding through the FLIPPR project (www.flippr.at).

References
S. Sugaya, M. Yamada, and M. Seki, â??Observation of non-spherical particle behaviors for continuous shape-based separation using hydrodynamic filtrationâ?, Biomicrofluidics, 5, 2011, 024103:1-13.

S. Dong, M. Salcudean, and I. Gartshore, â??The effect of slot shape on the performance of a pressure screenâ?, Screening, Tappi Journal, 4, 2004, 3-7.

R. Kerekes, â??Rheology of fibre suspensions in papermaking: An overview of recent researchâ?, Nordic Pulp and Paper Research Journal, 21, 2006, 598-612.