Mixing fluids efficiently in confined spaces? Let viscous fingers do the stirring

May 12, 2011

By Denise Brehm
Civil & Environmental Engineering

Getting two fluids to mix in small or confined spaces is a big problem in many industries where, for instance, the introduction of one fluid can help extract another — like water pumped underground can release oil trapped in porous rock — or where the mixing of liquids is the essential point of the process. A key example of the latter is microfluidics technology, which allows for the controlled manipulation of fluids in miniscule channels often only a few hundred nanometers wide.

Microfluidic devices were first introduced in the 1980s and for many years were best known for their use in ink-jet printers, but have since been introduced in other fields, including the chemical analysis of blood or other sera in lab-on-a-chip technologies. These devices — usually not much larger than a stick of chewing gum — sometimes rely on nano-sized moving components, the geometry of the grooved channels or pulsed injections to induce a mixing of the fluids. But researchers in MIT’s Department of Civil and Environmental Engineering suggest that a simpler method might be equally, if not more, effective.

“Getting two fluids to mix in a very tight space is difficult because there’s not much room for a disorderly flow,” said Professor Ruben