Analysis and measurements of mixing in pressure-driven microchannel flow

Abstract

The mixing phenomena for two fluid streams in pressure-driven rectangular microchannels are analyzed and directly compared with the measurements of mixing intensity for a wide range of aspect ratio (width/depth = 1-20). In the analysis, the three-dimensional transport equation for species mixing was solved using the spectral method in a dimensionless fashion covering a large regime of the normalized downstream distance. The analysis reveals the details of non-uniform mixing process, which originates from the top and bottom walls of the channel and stretches out toward the center of the channel, and its transition to uniformity. Employing different length scales for the non-uniform and uniform mixing regimes, the growth of mixing intensity can be expressed in a simple relationship for various aspect ratios in the large range. The mixing experiments were carried out on silicon- and poly(methyl methacrylate) (PMMA)-based T-type micromixers utilizing fluids of pH indicator (in silicon channel) and fluorescent dye (in PMMA channel) to evaluate the mixing intensity based on flow visualization images. Using conventional microscopes, the experiments demonstrate the mixing intensity as a power law of the stream velocity for all the microfluidic channels tested. The variations of measured mixing intensity with the normalized downstream distance are found in favorable agreement with the numerical simulations. The comparison between the experiments and simulations tells the capabilities and limitations on the use of conventional microscopes to measure the mixing performance

Coherent anti-Stokes Raman scattering microscopy for quantitative characterization of mixing and flow in microfluidics

“…Imaging local concentration or flow profiles has been demonstrated by fluorescence-based techniques, including particle image velocimetry and scalar fluorescence studies [10,11], light microscopy [12], confocal fluorescence microscopy [13], and multiphoton microscopy [14]. However, to follow untagged molecules, especially rapid diffusers-small molecules that typically do not fluoresce-an alternative Raman-based approach is attractive, directly quantifying local concentration with high chemical specificity by making use of inherent molecular vibrations of molecules.…”

A depthwise averaging solution for cross-stream diffusion in a Y-micromixer by considering thick electrical double layers and nonlinear rheology

“…In a subsequent work, Lam et al (2005) studied the dispersion of analytes in a Y-shaped micromixer by employing a depthwise averaging approach. More recent works are also reported on the subject matter of molecular diffusion in a Y/T-sensor, including both theoretical (Chen et al 2006;Wang et al 2006;Sullivan et al 2007;Salmon and Ajdari 2007;Gorman and Wikswo 2008;Broboana et al 2011;Chakraborty et al 2012;Song et al 2012;Mason et al 2013) and experimental researches (Chen et al 2006;Broboana et al 2011;Chakraborty et al 2012).…”

“…Among various essential functions in LOC devices is mixing of two or more fluids usually containing different concentrations of the targeted samples (Chen et al 2006). Due to the limitations of the microfabrication technology, simple micromixers such as the Y/T-sensor are usually preferred in the design of LOCs.…”

Hydrodynamic Focusing in Microfluidic Devices

“…However, little is known about this phenomenon on a basic level. So far, the papers on hydrodynamics of fluid focusing in microchannels present theoretical approach based on analytical solution of the flow in a rectangular cross-section channel (Chen et al, 2006;Solli et al, 2006;Wu and Nguyen, 2005 a,b,c).…”