Microfluidic valves for flow control at low Reynolds numbers

Fluidics is a technology of generating and controlling fluid flows — preferably without the action of mechanical moving components. Microfluidics perform these tasks in small, typically micronsized structures. Essential part of almost all microfluidic systems are flow control valves. The basic problem is the low Reynolds numberRe: inertial effects used in large-scale fluidics are too small relative to viscous dissipation. New approaches, such as pressure or electrokinetic driving are required. In the subdynamic, viscosity dominated flow regime, Re ceases to be of importance and for pressure-driven valves a new characterisation number was to be introduced. An example of a diverter valve, developed by the author, is described and the meaning of the new dimensionless parameter is demonstrated.