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Constructal theory is this mental viewing:
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(i)
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The generation of design (configuration, pattern, geometry) in nature is a physics phenomenon that unites all animate and inanimate systems, and
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(ii)
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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)
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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.
References
A. Bejan, Advanced Engineering Thermodynamics,
Wiley, 2nd edition, 1997, 896 p. ISBN 0471148806
A. Bejan, Shape and Structure, from Engineering to
Nature , Cambridge University Press, Cambridge, UK, 2000, 324 p. ISBN 0521793882
"Bejan's Constructal
Theory of Shape and Structure" Edited by Rui N. Rosa, A. Heitor Reis & A. F. Miguel, Evora Geophysics Center, Portugal, 2004, ISBN 972-9039-75-5
A. H. Reis, A. F. Miguel , M. Aydin, Constructal
theory of flow architecture of the lungs, Journal of Medical Physics, May
2004, Volume 31, Issue 5, pp. 1135-1140.
A. Bejan, S. Lorente, La Loi Constructale, L'Harmattan, Paris, 2005. ISBN 2-7475-8417-8
A. Bejan, S. Lorente, Constructal theory of generation of configuration in nature and engineering, Journal of Applied Physics, 2006, Volume 100, no. 041301.
A. Bejan, S. Lorente, Design with Constructal Theory, Wiley , 2008, ISBN: 978-0-471-99816-7.
Partly adapted from Wikipedia, the free encyclopedia
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