Constructal theory of pattern formation

. This review article shows that the occurrence of macroscopic flow configuration is a universal natural phenomenon that can be explained and predicted on the basis of a principle of physics (the constructal law): "For a flow system to persist in time (to survive) it must evolve in such a way that it provides easier and easier access to the currents that flow through it". The examples given in this article come from natural inanimate flow systems with configuration: duct cross-sections, open channel cross-sections, tree-shaped flow architectures, and turbulent flow structure (e.g., eddies, laminar lengths before transition). Other examples that are treated in the literature, and which support the constructal law, are wedge-shape of turbulent shear layers, jets and plumes, the frequency of vortex shedding, Bénard convection in fluids and fluid-saturated porous media, dendritic solidification, the coalescence of solid parcels suspended in a flow, global atmospheric and oceanic circulation and climate, and virtually all architectural features of animal design. The constructal law stresses the importance of reserving a place for pure theory in research, and for constantly searching for new physics – new summarizing principles that are general, hence useful.