The promise of design evolution: Adrian Bejan's new look at life and machines

Sometimes it helps to step outside your specialty and read publications that view the familiar world from entirely new perspectives.

Professor Adrian Bejan's work falls into this category.

Featured on the American Society of Mechanical Engineers (ASME) website Oct. 28 is an essay by Bejan that looks at engineering in the broadest possible terms. Titled "The Promise of Design Evolution," the essay is extracted from Bejan's 2020 book, "Freedom and Evolution: Hierarchy in Nature, Society and Science."

Bejan's specific message in the essay is for engineers to look at design with an understanding of "the limit between the possible and the impossible, and how to push the limit, if possible." 

But he cautions that beyond a certain point of performance, design improvements have diminishing returns.

Bejan frames the problem into a larger perspective, which may be useful in the fields of biology, geophysics, ecology, and perhaps those in the social or political arenas hoping to improve society.

Asked to summarize his main message, Bejan told Current Science Daily: "First, evolution is a universal phenomenon, and belongs in physics." 

It is, of course, most familiar in biology, he said.

"But if we open our eyes to the meaning of evolution, which means discerning the changes in a particular direction over time," evolution is in every realm, he said.

"Everywhere you look," Bejan said, there is a "tendency of things to flow together...not just to birds and fish. Dust particles and debris also flow together. This tendency is universal, a natural phenomenon. And nature covers everything."

Bejan's second main point is freedom. 

"The universal meaning of evolution is another name for freedom to change," he told Current Science Daily. "The object that evolves does so because it is endowed with certain features that allow it to change – to change shape, size, direction of movement."

People talk about limited resources, he said. 

"Those words sound like lack of freedom, but they don't represent that," he said. "If you have a sack with a finite volume, inside the sack there's infinite freedom to morph. Everything that you may decide to pour into the sack has infinite freedom to bounce up and down, right or left, in a particular configuration that is not cast in stone."

Bejan gave the example of the piston moving in and out in an engine, which has the freedom to change the volume of the compression chamber.

The constructal law

In 1996, Bejan proposed a new law of physics: the constructal law. 

"If evolution is a phenomenon of physics," he said, then it must have its own law. "The constructal law states that for a finite flow system to persist in time, it evolves with freedom such that it provides greater access to what flows.

"I chose these words very carefully to make sure that I covered everything: blood flow, river flow, animal migration in Zambia, and so on," he said.

At the time, he was working on entropy optimization and studying the cooling of miniaturized electronic components. He specifically described an efficient way to design flow in electric components from smaller paths to larger ones, branching in a similar way to how things flow in living things.

Since he first proposed it, the constructal law has been mathematized and applied in many disciplines: physics, biology, geophysics, ecology, and of course, engineering. 

"Engineering is the domain in which we see the evolution of the modern human," he said. "We are in fact not naked apes; we are encapsulated in human ingenuity–machines, clothing, available food. The list is absolutely endless about how powerless we would be without the things that we are used to and take for granted.

"The direction of evolution is toward greater access, which means easier flowing or greater efficiency, or longer lifetime," Bejan said. "These words describe the direction or hope, or optimism, or confidence. In this case, if you give something freedom to change, that something will be better, longer lasting, tomorrow."

Bejan is a J.A. Jones Distinguished Professor of Mechanical Engineering at Duke University, where he teaches thermodynamics. He's written 30 books and received many awards for his work. 

A hands-on beginning

Bejan credits his early work with hands-on biology as providing the imagery in the constructal law.

As a youth in Romania, he helped his father, a veterinarian, perform surgery with large animals in the field. 

"I saw the insides, the recovery of the animal, and I saw death, as a little boy, lots of blood and screams. In Romania, there was no anesthesia in that profession at the time," Bejan explained.

His childhood experience enabled him to "develop a feel for the imagery that comes from that. It has served me greatly in engineering. Because engineering is really much simpler than what goes on in the machinery of the animal body. The perfection there is amazing."

"These days with computers and all sorts of other simulation techniques people are trying to emulate what goes on in the natural design, because the natural design has the infinite freedom to morph," Bejan said.