Constructal Theory and its Relevance to Green Energy

Constructal theory is the thought that the generation of flow configurations is a phenomenon of physics. Flow configuration, such as the trees of river basins, lungs and city traffic unite the natural with the engineered, and the animate with the inanimate. The physics principle that accounts for the generation of flow configuration everywhere is the constructal law (Bejan, 1997 Bejan, A. 1997. Advanced Engineering Thermodynamics, 2nd, New York: Wiley. [Google Scholar], p. 807): “For a finite-size flow system to persist (to survive) it must morph in time such that it provides easier access to the currents that flow through it”. Why is the constructal law relevant to green energy? For lack of an official definition of “green energy”, we assume that green energy means “man going about his business without changing the environment much”. This thought defines the plane on which constructal theory is relevant. How can human action change the environment the least? The answer is delivered by the constructal law, which prescribes the ways in which humans can engineer machines that use minimal fossil fuels. Everything that Sadi Carnot (1824) Carnot, S. 1824. Reflections on the Motive Power of Fire, and on Machines Fitted to Develop that Power, Paris: Bachelier. [Google Scholar] said about making better machines is the constructal law, and is relevant to green energy. To persist in time (to survive), our flows must flow most easily (most efficiently) and be optimally matched to (i.e., in harmony with) the flows of the environment. Our trees of energy production, economics, business and garbage disposal must “mate” optimally with the trees of the environment (river basins, atmospheric and oceanic circulation).