“Constructal Theory: From Engineering to Physics, and How Flow Systems Develop Shape and Structure”

Constructal theory and its applications to various fields ranging from engineering to natural living and inanimate systems, and to social organization and economics, are reviewed in this paper. The constructal law states that if a system has freedom to morph it develops in time the flow architecture that provides easier access to the currents that flow through it. It is shown how constructal theory provides a unifying picture for the development of flow architectures in systems with internal flows (e.g., mass, heat, electricity, goods, and people). Early and recent works on constructal theory by various authors covering the fields of heat and mass transfer in engineered systems, inanimate flow structures (river basins, global circulations) living structures, social organization, and economics are reviewed. The relation between the constructal law and the thermodynamic optimization method of entropy generation minimization is outlined. The constructal law is a self-standing principle, which is distinct from the Second Law of Thermodynamics. The place of the constructal law among other fundamental principles, such as the Second Law, the principle of least action and the principles of symmetry and invariance is also presented. The review ends with the epistemological and philosophical implications of the constructal law

“Exergy based analysis of economic sustainability”

Exergy is presented here as the physical prime-mover of economic systems, and an exergy based concept of value is proposed in this paper. The main exergy fluxes are identified as those carried by raw exergy (primary sources), raw materials, usable exergy and exergy embodied in manufactured commodities. It is shown how efficiency of exergy use is the physical basis for competitiveness and how exergy content (value)can be assigned to skillfulness and expertise. Sustainability of economic systems is analyzed in the light of competitiveness and ability to take extra exergy taken from markets. It is also shown that in competitive economies the ratio (raw exergy)/(total value) tends to decrease, therefore indicating extra exergy from the markets, and this trend is illustrated with the case of the US economy. Finally, the average electricity price in the markets was proposed as a provisional correspondence between exergy content and price of commodities

Constructal view of scaling laws of river basins

River basins are examples of naturally organized flow architectures whose scaling properties have been noticed long ago. Based on data of geometric characteristics, Horton [Horton, R.E., 1932. Drainage basin characteristics. EOS Trans. AGU 13, 350–361.], Hack [Hack, J.T., 1957. Studies of longitudinal profiles in Virginia and Maryland. USGS Professional Papers 294-B, Washington DC, pp. 46–97.], and Melton [Melton, M.A, 1958. Correlation structure of morphometric properties of drainage systems and their controlling agents. J. of Geology 66, 35–56.] proposed scaling laws that are considered to describe rather accurately the actual river basins. What we show here is that these scaling laws can be anticipated based on Constructal Theory, which views the pathways by which drainage networks develop in a basin not as the result of chance but as flow architectures that originate naturally as the result of minimization of the overall resistance to flow (Constructal Law)

Natural flow patterns and structured people dynamics: a constructal view

Constructal theory that has been successfully applied to planetary circulations and climate and to river basin morphology is shown to provide a useful framework for describing flows of people. We showed here, with simple examples, that intuitive rules of traffic organization can be anticipated based on principle, i.e., based on the Constructal Law. In addition, and similarly to the case of flows of inanimate matter, in the case of flows of people, flow patterns emerge as a necessary consequence of reduction of global flow resistances. These flow patterns point to decreasing resistivity to flows of people and commodities. Pathway length varies inversely with resistivity while pathway number increases with resistivity

The changing energy paradigm, challenges, and new developments

Editorial of the Special Issue of the International Journal of Energy Researc

Coal and fuel burning effects on the atmosphere as mediated by the atmospheric electric field and galactic cosmic rays flux

Abstract: Emissions into the atmosphere of Greenhouse Gases (GHGs) and particulate matter resulting from fossil fuel burning are considered to be the main anthropogenic forcing on the global climate. We show here that the external cyclic influences of cosmic origin that modulate the earth’s climate may either reinforce or mitigate the ‘local’ terrestrial forcings. Among the external influences is cosmic radiation, whose intensity shows a cyclic variation of 11 years, accompanying the 11-year cycle of solar activity. We put forward a mechanism to explain how the emission of particulate matter into the atmosphere might influence global lightning activity. With respect to global lightning activity, we show why, during the 11-year cycle, the influence of an increase in particulate matter concentration in the atmosphere may be negligible in some years, while it will be reinforced in other years, depending on the place of the years in the cycle. We also remark that the effect on global warming of fossil fuel burning is also modulated by the cosmic ray flux, whose influence is mediated by the variation that it promotes on the cloud cover

Effects of porosity in a model of corrosion and passive layer growth

We introduce a stochastic lattice model to investigate the effects of pore formation in a passive layer grown with products of metal corrosion. It considers that an anionic species diffuses across that layer and reacts at the corrosion front (metal-oxide interface), producing a random distribution of compact regions and large pores, respectively represented by O (oxide) and P (pore) sites. O sites are assumed to have very small pores, so that the fraction $\Phi$ of P sites is an estimate of the porosity, and the ratio between anion diffusion coefficients in those regions is $D_{\text r}<1$. Simulation results without the large pores ($\Phi =0$) are similar to those of a formerly studied model of corrosion and passivation and are explained by a scaling approach. If $\Phi >0$ and $D_{\text r}\ll 1$, significant changes are observed in passive layer growth and corrosion front roughness. For small $\Phi$, a slowdown of the growth rate is observed, which is interpreted as a consequence of the confinement of anions in isolated pores for long times. However, the presence of large pores near the corrosion front increases the frequency of reactions at those regions, which leads to an increase in the roughness of that front. This model may be a first step to represent defects in a passive layer which favor pitting corrosion.Comment: 8 pages, 6 figure

Role of Sorption Isotherms in the Analysis of Coupled Heat and Mass Fluxes in Porous Media

The aim of this work is to show the importance of the sorption isotherms in the study of the heat and mass fluxes in unsaturated porous media. General forms of the heat and mass fluxes are presented in terms of experimentally accessible quantities. The role of the isotherm slope in the coupling of heat and mass fluxes and its influence on the effective permeability are shown. Separate relations for vapor and liquid fluxes through the porous medium are presented as functions of the temperature and the isotherm slopes. Nonstationary isothermal mass flux is also analyzed, a relaxation time for this process is identifled, and its relation to the isotherm slope is also discussed