Editing Mixing (process engineering) (section)

== Mixing in microfluidics ==
When scaled down to the microscale, fluid mixing behaves radically different.<ref>{{cite journal|last=Nguyen|first=Nam-Trung|author2=Wu, Zhigang|title=Micromixers—a review|journal=Journal of Micromechanics and Microengineering|date=1 February 2005|volume=15|issue=2|pages=R1–R16|doi=10.1088/0960-1317/15/2/R01|bibcode = 2005JMiMi..15R...1N |s2cid=16772224|url=https://semanticscholar.org/paper/47df8e4ff4ea24d987154cd0224eb43d6dd15a24}}</ref><ref>{{cite web|url=http://redbudlabs.com/microfluidic-mixing/|title=Microfluidic Mixing - Redbud Labs|website=redbudlabs.com|access-date=26 April 2018|url-status=live|archive-url=https://web.archive.org/web/20180102092036/https://redbudlabs.com/microfluidic-mixing/|archive-date=2 January 2018|df=dmy-all}}</ref> This is typically at sizes from a couple (2 or 3) millimeters down to the nanometer range.  At this size range normal [[advection]] does not happen unless it is forced by a hydraulic pressure gradient. [[Diffusion]] is the dominant mechanism whereby two different fluids come together. Diffusion is a relatively slow process. Hence a number of researchers had to devise ways to get the two fluids to mix. This involved Y junctions, T junctions, three-way intersections and designs where the [[interface (matter)|interfacial]] area between the two fluids is maximized. Beyond just interfacing the two liquids people also made twisting channels to force the two fluids to mix. These included multilayered devices where the fluids would corkscrew, looped devices where the fluids would flow around obstructions and wavy devices where the channel would constrict and flare out. Additionally channels with features on the walls like notches or groves were tried.{{Cn|date=March 2025}}

One way to know if mixing is happening due to advection or diffusion is by finding the [[Peclet number]]. It is the ratio of [[advection]] to [[diffusion]]. At high Peclet numbers (>&nbsp;1), advection dominates. At low Peclet numbers (<&nbsp;1), diffusion dominates.{{Cn|date=March 2025}}