This chapter discusses second-law analysis in heat transfer and entropy generation minimization in thermal design. It describes the derivation of the Gouy–Stodola theorem, the basis for entropy generation minimization in the conceptual design of heat transfer equipment. Appropriate analytical tools, such as the entropy generation number N s are devised for the task of estimating the destruction of available work in the processes involving heat transfer. However, the entropy generation number concept is considerably more general since it can be used to quantitatively describe the degree of irreversibility of engineering components and processes that do not draw their irreversibility solely from heat transfer. The examples considered in this article ranged from the irreversibility associated with some of the most fundamental convective heat transfer processes, to the minimum irreversibility design of one-dimensional insulations such as the main counterflow heat exchanger of a helium liquefaction plant.
This is a review of the theoretical and applied progress made based on the Constructal law of design and evolution in nature, with emphasis on the last decade. The Constructal law is the law of physics that accounts for the natural tendency of all flow systems (animate and inanimate) to change into configurations that offer progressively greater flow access over time. The progress made with the Constructal law covers the broadest range of science, from heat and fluid flow and geophysics, to animal design, technology evolution, and social organization (economics, government). This review presents the state of this fast growing field, and draws attention to newly opened directions for original research. The Constructal law places the concepts of life, design, and evolution in physics.
No abstract is provided for this article.
This article describes numerically the time evolution of an expanding mixture of hot spherical particles, steam, and water. It is assumed that at time t = 0 the mixture components are distributed uniformly through Ike mixture volume. The mixture expands against a body of water in which it is immersed. The expansion is due to steam generation; it is assumed that the hot particles remain equidistant as the mixture expands. The numerical procedure is based on the moving finite element method. The fluid particles are distributed throughout the domain and are moved in time in a Lagrangian manner to simulate the change of the domain configuration. Mathematically, the problem is formulated as a nonlinear initial boundary value problem with unknown quantities of an objective Junction (velocity potential) and the profile of the domain. The governing equation is discretized spacewise using the Galerkin finite element method. During expansion, the number of mesh elements remains unchanged, while the location of the nodes changes. The movement of the mesh nodes is attacked to the movement of the flow. The focus is on the energy conversion efficiency of the process, i.e., on the extent to which the heat released by the hot material is converted into kinetic energy. The results document the effects of changing the hot-particle size and water pool size. It is shown that the efficiency decreases almost inversely with time and that for times in the 1-ms range it has values of the order of 1%.
Constructal Theory of Social Dynamics brings together for the first time social scientists and engineers to develop a predictive theory of social organization, as a conglomerate of mating flows that morph in time to flow more easily (people, goods, money, energy, information). These flows have objectives (e.g., minimization of effort, travel time, cost), and the objectives clash with global constraints (space, time, resources). The result is organization (flow architecture) derived from one principle of configuration evolution in time (the constructal law): "for a flow system to persist in time, its configuration must morph such that it provides easier access to its streams." Constructal theory predicts animal design and geophysical flows, and makes evolution a part of physics. In the social sciences, there is substantial literature based on the use of optima to deduce social, population and economic dynamics. The constructal approach of this book links social sciences with physics, biology and engineering. The book explores the deterministic principle that generates a broad array of patterned phenomena, in demography, geography, communications, hierarchy, and multiple scales. Examples are the distribution of living settlements, the occurrence of flow structure inside each settlement, ‘development’ as the relation between fast-flowing societies and advancement and wealth, migration patterns, and globalization. Constructal Theory of Social Dynamics is novel and important because it puts the occurrence of social organization on a scientific basis. It brings social organization under the same physics principle that accounts for the generation of flow architecture (design) in geophysical flows, animal design, and engineered flows. This exploratory work adds a dose of determinism to the modeling and predicting of societal flows.
In this paper we address database-related issues in the emerging application field of ITS (Intelligent Transportation Systems). In this context we propose and study two cooperative driving scenarios: on-the-fty highway alert scenario and mutual driving group scenario. Vehicles cooperate and coordinate their actions by exchanging information, hence the need for database technologies such as consistency, replication, and query optimization. Technical requirements and suitability of technologies such as wireless and peer-to-peer communication and mobile ad-hoc networks are discussed. We introduce the notion of a peer-dependent query for the application environment.
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.
Here we show that the emergence of scaling laws in inanimate (geophysical) flow systems is analogous to the emergence of allometric laws in animate (biological) flow systems, and that features of evolutionary “design” in nature can be predicted based on a principle of physics (the constructal law): “For a finite-size flow system to persist in time (to live) it must evolve in such a way that it provides easier and easier access to its currents”, meaning that the configuration and function of flow systems change over time in a predictable way that improves function, distributes imperfection, and creates geometries that best arrange high and low resistance areas or volumes. This theoretical unification of the phenomena of animate and inanimate flow design generation is illustrated with examples from biology (lung design, animal locomotion) and the physics of fluid flow (river basins, turbulent flow structure, self-lubrication). The place of this design-generation principle as a self-standing law in thermodynamics is discussed. Natural flow systems evolve by acquiring flow configuration in a definite direction in time: existing configurations are replaced by easier flowing configurations.
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.
Here we show that the trends in four sports are united by the evolutionary constructal design of all animal locomotion.The trend is toward greater effi ciency in the falling-forward movement of the body, and this is why the evolution of the throwing motion unites team sports (baseball, hockey) with individual sports (golf, boxing, running and swimming).Records during the past 100 years indicate that in these sports the trend has been toward bigger and taller bodies, which possess greater speed of falling forward and throwing, greater force, and greater throwing distance.Equipment technology (golf balls, hockey sticks) has evolved in the same direction.In sum, the evolution of sports is in accord with the constructal law, and constitutes a "laboratory" for witnessing the evolution of biological design in our lifetime.
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...
A novel heat exchanger architecture was investigated, in which each fluid pathway transitions through the heat exchanger from tube-flow to shell-flow, or from shell-flow to tube-flow. The heat exchangers (HX) consisted of two plenums filled with tube bundles and a solid core of Counterflow channels Sandwiched between Plenums (CSP). To allow a high packing in the core region, a non-circular, e.g., triangular, cross-section tube shape was employed. In this exploratory study of the proposed CSP HXs, prototypes were fabricated by Laser Powder Bed Fusion additive manufacturing. Several challenges posed by the laser-powder-bed fabrication were presented and design solutions for additive manufacturing were discussed. Two different CSP HX were 3D printed, one in which the core region was placed midway between the end plates in the HX, and another one in which the core region was offset toward one end of the HX. The performance of the CSP HXs was evaluated against an off-the-shelf 5 kW shell-and-tube heat exchanger, considered as the baseline heat exchanger. Each of the baseline HX and six CSP HXs configurations were tested at three different flow rates for R245fa (cold fluid) while inlet conditions for the water (hot fluid) were not changed, for a total of 21 tests. It was found that the heat load for three CSP HXs configurations shows excellent thermal performance as compared to that of the baseline HX. The overall heat transfer coefficient for two CSP HX configurations was higher than that of the baseline by 16 to 32%. Although the proposed HXs did not outperform the commercial baseline HX in all aspects, the reported thermohydraulic performance in this first embodiment of the proposed HX concept indicated that the CSP concept offers a new path towards more efficient and more compact heat exchangers.
We address the fundamental problem of determining the optimal history (regime of operation) of a battery so that the work output is maximum. The essential features of the problem are: (i) the life of the battery is constrained, (ii) the battery has an internal resistance through which it can lose its charge even at open circuit, and (iii) the battery is connected to an electric motor with finite winding resistance. The optimal regime of time-dependent operation is determined based on variational calculus. It is shown that the maximized work output is smaller than the exergy stored initially in the battery, and decreases as the motor resistance increases. The exergy stored in a battery cannot be recovered fully as soon as the resistance of the external circuit is finite, no matter how small.
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 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.
