Constructal Theory

The main principle of the constructal theory is that every system is destined to remain imperfect.

According to this, the best that can be done is to optimally distribute the imperfections of the system, and this optimal distribution of imperfection will generate the geometry or shape of the studied system.

The constructal theory of global optimization under local constraints explains in a simple manner the shapes that arise in nature. It is the thought that flow architecture comes from a principle of maximization of flow access, in time, and in flow configuration that are free to morph.

The Constructal law proclaims a tendency in time about the generation of animate and inanimate flow systems: “the maximization of access for the currents that flows through a morphing flow system “. This theory replaces the belief that nature is fractal, and allow one to design and analyse systems under constraints in a quest for optimality.

This theory allows the design and understanding of natural systems, thermal dissipators, communication networks, etc.

The constructal theory was invented by Adrian Bejan.

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 of Mechanical Engineering at Duke University, Durham.

Bejan’s research areas cover: entropy generation minimization, exergy analysis, condensation, 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, in the constructal theory’s point of view, the naturally optimized forms such as rivers, trees and branches, lungs and also the engineered forms coming from a constructal optimization process.

Principles

For example, in point-area and point-volume flows, constructal theory predicts tree architectures, such flows have displaying at least two regimes: one highly resistive and a less resisitive one, and it can be applied at any scale: from macroscopic to microscopic systems.

The main principle of the constructal theory is that every system is destined to remain imperfect.

According to this, the best that can be done is to optimally distribute the imperfections of the system, and this optimal distribution of imperfection will generate the geometry or shape of the studied system.

The constructal way of distributing the system’s imperfection is to put the more resistive regime at the smallest scale of the system. The constructal law is the principle that generates the perfect form, which is the least imperfect form possible.

Modern edifices such as the Atlanta airport illustrates the constructal principle of equipartition of time (resistance), or the optimal distribution of imperfection. Several objectives were pursued in the development of this tree-shaped flow structure: the minimization of travel time for pedestrians, the minimization of time and transportation cost for the goods flowing between the terminal and each gate. The airport flows are a tree. In accordance with constructal theory, the time to walk on a concourse is the same (~5 min) as the time to ride on the train.

Constructal law

The constructal principle was enonced in 1996 by Adrian Bejan as follows: “For a finite-size system to persist in time (to live), it must evolve in such a way that it provides easier access to the imposed currents that flow through it.”

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