An experimental characterization of a tunable separation device

Abstract

By the use of an experimental setup for microfluidic flows, we have characterized the separation and concentration characteristics of the so-called Trilobite^™ separation unit. Our separation unit consists of microfluidic channels and an elliptical separation geometry with a solid and a permeable wall region. We show that it is possible to adjust the thickness of different flow layers by changing the flow rates and pressure drop over the permeable wall. For high pressure drops, the separator shows promising concentration characteristics. For low pressure drops, an increase in flow rate results in a thinning of the flow layers. For sufficiently high flow rates, it should therefore be possible to create flow layers sufficiently thin that the particle separation is entirely dominated by hydrodynamic forces. This, in turn, will enable clog-free particle separation.

Appendix: Calculation of the total flux

The total flux, $Q_{\rm tot}=Q_{p}$ + $Q_{c}$, is slightly changed when the saddle point is moved from the upstream to the downstream position. The change, however, is less than 2% for the lowest flow rate, corresponding to $Re=2.8$, and less than 1% for the intermediate flow rate ($Re=29$), and could be neglected. The permeate flow rate $Q_p$ for $Re=58$ and downstream saddle point position is unknown because parts of the permeate flow layer is outside the field-of-view of the objective lens. Therefore, the total flow rate is unknown. But since $Q_{\rm tot}$ changes by 1% for $Re=29$ when the saddle point is moved between the upstream and downstream position, we assume that this is also true for the highest flow rate ($Re=58$). We therefore assumed that the total flux $Q_{\rm tot}$ for the downstream saddle point was the same as for the upstream saddle point, which we knew, and calculated the permeate flux from $Q_{p}=Q_{\rm tot} -Q_{c}$.