Mixing Fluids with the Flat Y-Mixer
Mixing is required for a variety of chemical operations, and the difficulty of mixing laminar flow streams presents one of the classic challenges in microfluidics. One classic trick to mix fluids in microfluidics is to laminate fluids in thin layers so that diffusion distances, and thus diffusion times, are made very small. In conventional microfluidics this requires special microfabrication and very accurate pumps, but it is trival to create similar mixers in paper. The image below shows a Y-mixer that achieves rapid mixing by stacking two strips of paper to create thin adjacent flow streams.
Fluids from two inlets mix rapidly as the flow streams join. A spacer is used to control the location of the fluid interface, and the orientation of the flow streams creates a short diffusion region that allows rapid mixing.
This arrangement provides very small diffusion distances (paper thickness, about 100 microns) and maximizes the interfacial area for diffusion. In the figure, a yellow fluid stream and a blue fluid stream rapidly interdiffuse to create a mixed green fluid. The paper Y-mixer is analogous to lamination mixers developed in microfluidics, but it is very easy to make and requires no pumps.
For more information on the paper mixer see:
“Microfluidics without pumps: reinventing the T-sensor and H-filter in paper networks,” Lab on a Chip (2011).
Jennifer L. Osborn, Barry Lutz, Elain Fu, Peter Kauffman, Dean Y. Stevens, and Paul Yager.
Department of Bioengineering, University of Washington, Seattle, WA, USA
For general background on low Reynolds number flows see:
“Biotechnology at low Reynolds numbers,” Brody, Yager, Goldstein, and Austin. Biophysical Journal, 71 (6), 3430-3441, (1996).