In this paper, we extend to the design of electric power distribution networks the constructal method of deducing the multiple dimensions of the network from the maximization of global system performance. Unlike earlier constructal designs of tree shaped networks, where the global objective was minimization of flow resistance and exergy destruction, in the present study, the global objective is minimization of the present worth total cost. The first half of the paper is a detailed account of all the components of the distribution system (hierarchy, voltage levels, lines, transformers) and the associated cost components that make up the global cost function. Emphasis is placed on the relations between length scales (radii, or reaches) at every voltage level and the costs of components and assemblies of components at every level and, ultimately, at the global level. It is shown that the global cost depends on multiple length scales, the load density (power consumption per unit of territory served) and the operating and economic characteristics of the voltage lines and transformers. Tradeoffs between the costs of lines and transformers exist at every voltage level, and this permits the multiple minimization of the global cost function. The optimized radii for each voltage level of the network are reported: they decrease at their own rates as the load density increases.
Enclosures heated from the side are most representative of porous systems that function while oriented vertically, as in the insulations for buildings, industrial cold-storage installations, and cryogenics. As in the earlier chapters, we begin with the most...
Constructal theory complements the analysis of thermodynamic systems by focusing on the flow configuration of the system, and on the relationship between configuration (design) and global performance. The design progress made in this emerging field is reviewed in a new book [1]. In this paper we outline our progress on developing flow architectures for a new class of smart materials: composites with vascular channels that provide volumetric flowing (bathing) and cooling.
This article is about evolutionary design and freedom and is based on my new book, Freedom and Evolution: Hierarchy in Nature, Society and Science [1]. There is a lot to say about this broad subject, therefore I’ve reduced it to the topics of thermodynamics, freedom and evolution, diversity and hierarchy, and science and freedom. First, I will present the terminology, which will be followed by the applications of the evolution of cooling technology for high-density heat-generating components in a packet. Finally, I will show why this book is important for you, the reader, as well as for the practitioner.
This is an analytical and numerical study of the exergy that can be delivered by a solar collector installation with temporary energy storage capability. In the first part of the study, the method of variational calculus is used to show that under conditions of time-dependent inlet and outlet flow rates, the total exergy delivered by the installation is maximum when the collector temperature is maintained at an optimum constant level throughout the insolation period. More realistic models of solar collectors with storage capability are analyzed in the second and third parts of the study. In each of the models considered, the analysis shows that the relative timing of the filling and discharge processes has a significant effect on the total exergy delivered by the installation. The main conclusion of the study is that the daily regime of operation of the collection/storage installation can be selected by design in order to maximize the harvesting of solar exergy per unit of collector area.
In this chapter we focus on the equation that expresses the first law of thermodynamics in a porous medium. We start with a simple situation in which the medium is isotropic and where radiative effects, viscous dissipation, and the work done by pressure changes are...
The paper proposes a conceptually new method for thermal insulation system optimization. The method, based on minimizing thermodynamic irreversibility, consists of externally controlling the variation of heat leak with temperature across the insulation. It is demonstrated that the useful power savings registered from applying this design philosophy are important. Prime candidates for this method are insulation systems facing high absolute temperature ratios and insulation systems in which the effective thermal conductivity increases with the absolute temperature. Three classes of thermal insulation systems are optimized based on this universal design procedure: one-dimensional continuous insulations, insulations with discontinuous temperature distribution and continuous insulations with internal heat generation.
This paper develops an alternative approach to evaluating the arbitrary constants found in Gill's solution for the boundary-layer free-convection regime in a vertical rectangular enclosure. The new method consists of calculating the net upward flow of energy through the enclosure and setting it equal to zero near the top and bottom boundaries of the cavity. The present method takes into account the impermeable and adiabatic properties of the horizontal end walls. The overall Nusselt number derived on this new basis is shown to agree well with available experimental and numerical heat-transfer correlations.
The minimum theoretical refrigerator power for cooling mechanical supports for a cryogenic apparatus is determined with the calculus of variations. A mathematical approach is developed that can be used to evaluate the thermal performance of any mechanical support which has fixed geometry. Four practical, non-optimum cooling arrangements are compared with the minimum power case. The comparison shows that a smaller refrigerator power is required when continuous cooling is provided at intermediate temperatures along the conducting support. A combination of two gas streams in series closely approximates the thermodynamically optimum cooling arrangement.
Technical Briefs Sliding Contact Melting: The Effect of Heat Transfer in the Solid Parts P. A. Litsek, P. A. Litsek Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27706 Search for other works by this author on: This Site PubMed Google Scholar A. Bejan A. Bejan Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27706 Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information P. A. Litsek Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27706 A. Bejan Department of Mechanical Engineering and Materials Science, Duke University, Durham, NC 27706 J. Heat Transfer. Aug 1990, 112(3): 808-812 (5 pages) https://doi.org/10.1115/1.2910465 Published Online: August 1, 1990 Article history Received: September 8, 1988 Revised: September 5, 1989 Online: May 23, 2008
No abstract is provided for this article.
Introduction to Thermal System Design. Thermodynamics, Modeling, and Design Analysis. Exergy Analysis. Heat Transfer, Modeling, and Design Analysis. Applications with Heat and Fluid Flow. Applications with Thermodynamics and Heat and Fluid Flow. Economic Analysis. Thermoeconomic Analysis and Evaluation. Thermoeconomic Optimization. Appendices. Index.
Thermodynamics is brief, simple, unambiguous and improving.Yet, confusion reigns in the field.The word "entropy" is pasted on almost any new thing, without any respect for its proper definition in thermodynamics.Every author bows to his own maximum or minimum principle, even when it contradicts English, not just thermodynamics.Minimizing resistance cannot be the same as maximizing resistance.Minimizing entropy generation cannot be the same as maximizing entropy generation.Because of the word "entropy", many believe that entropy generation minimization and maximization are covered by the second law, which is incorrect, twice.Because for an isolated system (or an adiabatic closed system) the second law states that the system entropy inventory increases during changes inside the system, many believe that the second law accounts for organization, evolution, and the arrow of time.This too is incorrect.It is time for a reality check, and this means to take a look at nature, at the physics, at the science of all the natural things that "happen".Here then is a review of the few, the noble, the laws with which in science we cover the few distinct phenomena that nature is made of.
In this chapter we focus on the equation that expresses the first law of thermodynamics in a porous medium. We start with a simple situation in which the medium is isotropic, and where radiative effects, viscous dissipation, and the work done by pressure changes are...
This paper reports theoretical solutions for the quasi-steady and time-dependent regimes of melting in the presence of natural convection in an enclosed phase-change material heated from the side. The first part consists of developing two boundary layer solutions for the flows near the heated wall and the solid-liquid interface, and then matching these solutions with a unique solution for the core of the liquid region. The second part of the paper outlines an analysis for the earlier, time-dependent regime, when the liquid counterflow through the slender gap convects heat in the vertical direction. This two-part analysis shows that the liquid superheat (Stefan number, Ste) has a sizeable effect on the flow and temperature fields. As Ste increases, the average melting rate decreases and the overall heat transfer rate into the enclosure increases.
In this article we rely on constructal theory to show that the hierarchy of universities is rigid, and that the explanation lies in the nature of education (science, news, information) as a natural fl ow system that bathes the globe most effectively. The article begins with two observations: (i) the rankings of the best engineering universities in the USA closely mirror the rankings of the universities that have the most names of researchers on the list of the most highly cited authors; and (ii) the log‐log plot of the number of highly cited authors of one school versus the rank of that school is nearly a straight line with slope between ‐1/2 and ‐1. The straight line is the same as the distribution of city sizes versus city rank throughout the history of Europe. From this follows the argument that the hierarchy of universities is tied to geography, to how each nodule of knowledge generation serves the area allocated to it. Education fl ows from point to area. The compounding of areas to cover the landscape is the origin of the hierarchical and stable arrangement of universities. The rank of a university is closely related to the visibility of its producers of ideas. The tapestry of a university on the landscape is predicted. All universities grow and improve in time (like all the river channels during the rain), but their hierarchy remains the same.
