Tree branching key to efficient flow in nature and novel...( DURHAM N.C. Nature in the simple fo...)

DURHAM, N.C. Nature, in the simple form of a tree canopy, appears to provide keen insights into the best way to design complex systems to move substances from one place to another, an essential ingredient in the development of novel "smart" materials.

Duke University engineers believe that an image of two tree canopies touching top-to-top can guide their efforts to most efficiently control the flow of liquids in new materials, including the next generation of aircraft and rocket "skins" that can self-repair when damaged, or self-cool when overheated.

"Examples of this branching design tendency are everywhere in nature, from the channels making up river deltas to the architecture of the human lung, where cascading pathways of air tubes deliver oxygen to tissues," said Adrian Bejan, J.A. Jones Professor of Mechanical Engineering at Duke's Pratt School of Engineering.

Developing the most efficient and effective manner of controlling flow is becoming increasingly important, as engineers strive to create the next generation of nanodevices and "smart" materials. The goal of this research is to create materials that act like human skin by delivering liquid healing agents through a network much like blood vessels. Materials such as these will need efficient delivery systems, Bejan said.

Working with Sylvie Lorente, professor of civil engineering at the University of Toulouse, France, Bejan found that the laws of constructal theory (http://www.constructal.org/), which he first described in 1996, could guide the creation of these novel "smart" materials.

The constructal theory is based on the principle that flow systems evolve to minimize imperfections, reducing friction or other forms of resistance, so that the least amount of useful energy is lost. The theory applies to virtually everything that moves, Bejan said.

"We examined a flow system that looks more
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