Tuesday, March 3, 2015

Book Review: Shape and Structure, From Engineering to Nature by Adrian Bejan

This is the first engineering book that kept me up late in suspense. It actually did. I couldn't wait to see what new phenomenon Adrian Bejan would tie into his constructal theory. What we have here is a book that starts off telling about how to build a system coolant that will most effectively cool a hot computer chip. It turns out that the best way to cool an area is to build something that looks an awful lot like a tree. And then how to build a system that will best drain a basin. That system looks like a tree. In three dimensions, Bejan discusses the best shape for a cross-section, which looks like the cross-section of a tree branch, or an artery. Then the best way to transfer heat intermittently is to have a regular rhythm that matches the rate of breathing or heartbeat. And the best way to arrange a city around a central facility. Yep, it's a tree.

This may sound like those mathematicians who see fractals everywhere, but it's different in a few crucial ways. For one thing, fractals are built top-down and continue to infinite detail. That doesn't fit the real world -- after all, atoms are not fractal. It has to stop somewhere. Rather, constructal theory starts with the smallest element that can move heat or matter, and then it builds and array of those elements, then an array of the arrays, and on up. The patterns look fractal but they are built very differently. And the most important thing is that (for all those phenomena listed above) they are predictive.

Only a few times does Bejan stretch his theory too far. A short passage on life and death, and some of the social applications, seem to not account for all the variables. But that means the theory covers only 98 different phenomena rather than 100. It's not that big a deal.

This is a truly unifying theory that explains how chemical things, biological things, and human-engineered things best distribute their flows. Bejan even gets a few philosophical implications in there (though I think there are many more to develop upon reflection). It's something to keep you up at night in a good way. This is what science is for.

1 comment:

Adrian Bejan said...

Thank you Ben,

Your readers may also like the book "Design in Nature", Doubleday, New York, 2012,

Current developments are reviewed at these blogs:


and at the 9th Constructal Law Conference, http://www.clc2015.eu/

Adrian Bejan
Duke University