Adrian Bejan-inventor of the constructal theory of global optimization under local constraints

Adrian Bejan (born September 24, 1948), Ph.D. (MIT, 1975) is a Romanian-born American professor of mechanical engineering and inventor of the constructal theory of global optimization under local constraints.

 He is J. A. Jones Distinguished Professor of Mechanical Engineering at Duke University.
 Professor Bejan's research covers a wide range of topics in thermodynamics, heat transfer, fluid mechanics, convection and porous media. More recently, he developed the constructal law of design in nature.



Professor Bejan is ranked among the 100 most highly cited authors worldwide in engineering (all fields, all countries), the Institute for Scientific Information, 2001. Professor Bejan has received 15 honorary doctorates from universities in 10 countries.
Adrian Bejan is the author of 23 books and 500 peer-referred articles.



Constructal theory is this mental viewing:

(i) The generation of design (configuration, pattern, geometry) in nature is a physics phenomenon that unites all animate and inanimate systems, and

(ii) This phenomenon is covered by the Constructal Law: "For a finite-size (flow) system to persist in time (to live), its configuration must evolve such that it provides easier and easier access to its currents." (Bejan, 1996)
The Constructal Law is about the time direction of the "movie" of design generation and evolution. It is not about optimality (min, max), end design, destiny or entropy.
The concept that the Constructal Law defines in Physics is "design" (configuration) as a phenomenon in time.

History

The constructal theory was developed by Adrian Bejan, Ph. D. MIT (1975) in the late 90's.
Professor Bejan taught at MIT until 1976 and is now J.A. Jones Distinguished Professor at Duke University, Durham.
Bejan's research areas cover: thermodynamics, heat transfer, design in nature, convection in porous media, transition to turbulence, etc.

 "Constructal" is a word created by Bejan, coming from the Latin verb construere, to construct, in order to designate the natural tendency of all flow systems to construct flow configurations, such as rivers, trees and branches, lungs and also the engineered forms coming from the constructal design-generation.

Examples

In point-area and point-volume flows, the constructal law predicts tree architectures. Such flows exhibit at least two regimes: one highly resistive and a less resistive one, and this applies at any scale: from macroscopic to microscopic systems.

Some domains of application

Application What flows Tree channels Interstitial spaces
Packages of electronics Heat High-conductivity inserts (blades, needles) Low conductivity substrate
Urban traffic People Low-resistance street car traffic Street walking in urban structure
River basins Water Low-resistance rivulet and rivers Darcy flow through porous media
Lungs Air Low-resistance airways, bronchial passages Diffusion in alveoli tissues
Circulatory system Blood Low-resistance blood vessels, capillaries, arteries, veins Diffusion in capillary tissues

According to the Constructal law, every system is destined to remain imperfect, i.e. with flow resistances
The natural constructal tendency then is to distribute the imperfections of the system, and this distribution of imperfection generates the shape and structure of the system.
The constructal way of distributing the imperfections is to put the more resistive regime at the smallest scale of the system.
Modern edifices such as the Atlanta airport illustrate the constructal principle of equipartition of time (resistance): the time to walk on a concourse is the same (~5 min) as the time to ride on the train.
The constructal law is predictive and has been verified numerous times. For example it has been used to predict: the proportionality between metabolic rate and body size raised to the power 3/4, the proportionality between breathing and heart beating times and body size raised to the power 1/4, the proportionality between the speed of all animals (flyers, runners, swimmers) and body mass raised to the power 1/6.

Bejan's Constructal Law also explains why we have a bronchial tree with 23 levels of bifurcation. The constructal law delivers in a purely deterministic way: the dimensions of the alveolar sac, the total length of the airways, the total alveolar surface area, and the total resistance to oxygen transport in the respiratory tree.