The micro-Particle Image Velocimetry (micro-PIV) was used to measure flow velocities in micro-channels in two passive micromixers: a microfluidic Venturi mixer and a microfluidic spiral mixer, both preceded by standard “Y” micromixers. The micro-devices were made of borosilicate glass, with micro-engineering techniques dedicated to micro-PIV measurements. The obtained velocity profiles show differences in the flow structure in both cases. The micro-PIV enables understanding the micro-flow phenomena and can help to increase reproducibility of micromixers in mass production.
In this paper we present the numerical simulation-based design of a new microfluidic device concept for electrophoretic mobility and (relative) concentration measurements of dilute mixtures. The device enables stationary focusing points for each species, where the locally applied pressure driven flow (PDF) counter balances the species electrokinetic velocity. The axial location of the focusing point, along with the PDF flowrate and applied electric field reveals the electrokinetic mobility of each species. Simultaneous measurement of the electroosmotic mobility of an electrically neutral specie can be utilized to calculate the electrophoretic mobility of charged species. The proposed device utilizes constant sample feeding, and results in time-steady measurements. Hence, the results are independent of the initial sample distribution and flow dynamics. In addition, the results are insensitive to the species diffusion for large Peclet number flows (Pe > 400), enabling relative concentration measurement of each specie in the dilute mixture.
We present a review of recent technical developments in Lattice Boltzmann Equations, as applied to single-phase flows with and without slip lenghts at the wall and for multi-phase flows in presence of hydrophobic walls. The interplay between roughness and hydrophobicity is discussed for microfluidics application. The issue of finite Knudsen effects is also addressed.