Latest Research in Microfluidics Highlights DFD Meeting

The burgeoning field of micro-fluid dynamics, which holds enormous potential for commercial applications, was a major focus of the annual fall meeting of the APS Division of Fluid Dynamics (DFD), held 19-21 November 2000, in Washington DC. Micro-fluidic dynamics is a key enabling factor in the miniaturization and integration of multiple functionality for chemical analysis and synthesis in handheld microdevices, which require efficient methods for transporting ultrasmall volumes of liquid through networked arrays.

The majority of such devices combine micromechanical and electric field driven methods for controlling flow in closed channels. However, researchers at Princeton University recently introduced a non-electronic means of flow control especially well suited to the construction of a chemical reactor on the surface of an integrated circuit. The design relies on thermocapillary transport of liquid streams or droplets on a surface produced by micropatterning a self-assembled monolayer. The chemical patterning confines the flowing liquid to selected pathways bearing a streamwise thermal gradient. Eventually, the researchers hope to use micropatterned temperature fields in differential mode to route liquid along selected pathways, and in absolute mode to induce chemical reactions at electronically addressable sites

At the University of California, Berkeley, researchers have fabricated a controllable single-bubble micro-pump, based on earlier work demonstrating that under certain conditions, thermally generated bubbles can rapidly and efficiently move fluid. In addition, a research initiative within the aerospace community is underway to study the feasibility of miniaturized "nanosatellites" with less than 1 kg of mass. These devices will require a corresponding miniaturization of the propulsion subsystem with thrust levels on the order of 10-500 uN. A team of researchers at the University of Vermont is developing a prototype MEMS-based H₂O₂ thruster capable of meeting these mission requirements.

Biofluid Dynamics

Biomedical investigators have increasingly realized that principles of fluid dynamics - especially an understanding of how hemodynamic forces and mass transport interact with the cells, proteins and molecules that constitute the arterial wall - play a major role in maintaining the health of human arteries, as well as contributing to arterial disease, according to Don Giddens of the Georgia Institute of Technology. For example, 3-D pulsatile blood flow in compliant arteries can now be described using computational fluid dynamics, with the potential to model blood flow in individual subjects. Giddens demonstrated how the local flow field can be manipulated to cause cellular proliferation in animal models, with important implications to the clinical problem of vascular grafts used to bypass diseased arteries. He also described recent fluid dynamical studies of the local shear stress on monocyte adhesion, and on expression of adhesion molecules on the endothelial cell surface.

Fluid Mechanics of the Earth's Core

Recent advances in numerical and laboratory modeling of the Earth's main magnetic field - which is induced by motions in the iron-rich liquid outer core (the geodynamo) - is revealing the fluid mechanics of the process by which the magnetic field is produced. Possible energy sources for the geodynamo include thermo-compositional convection and precession, with the former being the more likely option, according to Peter Olson (Johns Hopkins University). Olson reported that his numerical calculations of convection in rotating, electrically conducting spherical shells reveal that the columnar vortices contain large amounts of negative helicity in the northern hemisphere, and positive helicity in the southern hemisphere, and result in self-sustaining dynamo action.