901 publications from this institution
This paper discusses experimental observations of the meandering fall of light-weight tissue paper ribbons. The photographs show that the ribbons assume a sinusoidal shape with a unique wavelength which scales with the thickness of the airstream entrained by the ribbon.
No abstract is provided for this article.
This paper reports a complete theory of the melting that occurs in a confined porous medium saturated with phase-change material and heated from the side. Darcy flow characteristics are assumed for the liquid phase. The solid phase is isothermal and at the melting point. The first part of the paper reports a matched boundary layer solution for natural convection dominated melting in the quasi-steady regime. The second part reports a solution for the heat transfer during the two earlier regimes, pure conduction followed by mixed conduction and convection. Together, the two solutions cover the entire history of transient heating administered from the side. This theory shows that the liquid-side Stefan number has a profound effect on the heat transfer and melting rates.
This paper documents the effect of thermal expansion on a vascularized plate that is heated and loaded mechanically. Vascular cooling channels embedded in a circular plate provide cooling and mechanical strength. The coolant enters the plate from the center and leaves after it cools the plate to an allowable temperature limit. The mechanical strength of the plate decreases because of the embedded cooling channels. However, cooling the plate under an allowable temperature level decreases the thermal stresses. The mechanical strength of the plate which is heated and loaded mechanically at the same time can be increased by inserting cooling channels in it. The mechanical and thermofluid behavior of a vascularized plate was simulated numerically. The cooling channel configurations that provide the smallest peak temperature and von Mises stress are documented. There is one cooling channel configuration that is the best for the given set of boundary conditions and constraints; however, there is no single configuration that is best for all conditions.
Thermodynamic optimization and constructal designThis special issue focuses for the first time on a new development in thermodynamic analysis and optimization: the constructal method and the universal process of the generation of energy system configuration.Why is the generation of configuration important, and why focusing on it is new in science?We all learn that modern thermodynamics grew out of Sadi Carnot's contemplation of the functioning of fire-driven engines.The first law and the second law allow us to analyse and predict how a given heat engine will perform.This is powerful science; however, the world of flow systems (heat engines, animals, global circulation, etc.) shows that the performance of such systems increases in time.The first law and the second law are not enough.Performance increases because one flow configuration morphs into, or is replaced by a new configuration that performs better.This parade of better and better drawings is as much a part of physics as the conservation of energy (first law) and the fact that all things flow from high to low (second law).The principle that accounts for this universal tendency of flow systems in time is the constructal law, which was stated in 1996: for a finite-size flow system to persist in time (to live) it must evolve in such a way that it provides easier access to its currents.The generation of flow configuration in accordance with the constructal law is constructal design.The thought that the self-organized and self-optimized flow structures of nature (animate and inanimate) can be reasoned based on the constructal law is constructal theory.The generation of flow configuration belongs in thermodynamics, because starting with the fire-driven engine and ending with geophysical flows and living systems, the generation of flow configuration completes the deterministic edifice that until now rested on only two legs, the first law and the second law.Yildiz Technical University of Istanbul had the vision to organize the first school that taught this new, enlarged thermodynamics: The International Summer School of Thermodynamic Optimization and Constructal Design, 19-23 July 2004.Well-known professors were invited to lecture to an international audience of researchers from academia and industry.
Here, we show how to distribute multiple layers of insulation along a nonisothermal enclosure so that the total heat loss is minimal. The types and total amounts of insulation materials are fixed. Variables are the thicknesses of the insulation layers, their relative amounts, the temperature of the insulated surface, and the cross-sectional area of the enclosure. We show that, first, the structure of the multi-layer insulation must be such that the thicknesses of all the layers vary in the same way in the longitudinal direction x. Second, the x dependence of the enclosure cross-sectional area has a significant effect on the heat loss reduction associated with using the distributed insulation design. Greater reductions in heat loss are obtained when the enclosure is tapered such that it is narrower in the direction of the warm end. Third, the x dependence of the temperature distribution along the insulated wall has a significant effect on the reduction in heat loss through reduction in heat loss through the multi-layer insulation. Greater reductions are obtained when the wall temperature distribution is more convex. Even greater reductions in heat loss are possible when the three design features summarized previously are implemented simultaneously. Copyright © 2011 John Wiley & Sons, Ltd.
The new direction traced in this article is to vary freely and simultaneously the fin and flow channel aspect ratios in the search for the complete high-density heat transfer flow architecture. We show that when the combined solid and fluid volume is specified, and the fluid flow rate is known, it is possible to anticipate from theory the complete design (all the aspect ratios) of the flow configuration. The power to predict covers the overall heat transfer rate and the required pumping power. The configuration and performance owe their existence to the multiple degrees of freedom identified in the design, and exploited in the theory.
This paper extends to economics of the constructal theory of generation of shape and structure in natural flow systems that connect one point to a finite size area or volume. By invoking the principle of cost minimization in the transport of goods between a point and an area, it is possible to anticipate the dendritic pattern of transport routes that cover the area, and the shapes and numbers of the interstitial areas of the dendrite. It is also shown that by maximizing the revenue in transactions between a point and an area, it is possible to derive not only the dendritic pattern of routes and their interstices, but also the optimal size of the smallest (elemental) interstitial area. Every geometric detail of the dendritic structures is the result of a single (deterministic) generating principle. The refining of the performance of a rough design (e.g. rectangles-in-a-rectangle) pushes the design towards a structure that resembles a theoretically fractal structure (triangle-in-triangle). The concluding section shows that the law of optimal refraction of transport routes is a manifestation of the same principle and can be used to optimize further the dendritic patterns. The chief conclusion is that the constructal law of physics has a powerful and established analogue in economics: the law of parsimony. The constructal theory, as extended in this paper, unites the naturally-organized flow structures that occur spontaneously over a vast territory, from geophysics to biology and economics.
No abstract is provided for this article.
The First Law of Thermodynamics. The Second Law of Thermodynamics. The Two Laws Combined: The Destruction of Exergy. Single--Phase Systems. Exergy Analysis. Multiphase Systems. Chemically Reactive Systems. Power Generation. Solar Power. Refrigeration. Thermodynamic Optimization. Irreversible Thermodynamics. Constructal Theory of Organization in Nature. Appendix. About the Author. Indexes.
No abstract is provided for this article.
The first textbook to bridge the gap between three cornerstones of engineering education: fluid mechanics, thermodynamics and heat transfer. It provides an effective method to teach the thermodynamic (second law) aspects of heat and fluid flow processes, and shows how to use such processes in the design of energy-efficient devices. The text offers a wide range of original research to support the entropy generation minimazation'' philosophy and includes 250 references in the field of thermodynamic optimization and the thermodynamics of heat and fluid flow.
Dendritic flow architectures are being contemplated for thermal designs that provide high heat transfer densities for the cooling of electronics. Optimized tree networks maximize the flow access between one point (source, sink) and an infinity of points (line, area, volume). This paper is a fundamental study of a new class of dendritic flow architectures for thermal design: trees combined with closed-loop structures, as in the venation of leaves. The loops provide robustness to the design: the network continues to serve its assigned area even if one or more ducts are damaged. The study documents the achievement of performance and robustness systematically, by starting from the simplest architectures and proceeding toward the more complex, namely, point-circle networks with one loop size and two loop sizes, and networks with loops without and with branching levels. It is shown that the use of loops increases the global flow resistance relative to the dendritic design without loops. Damage, or removal of a duct from the network, also leads to an increase in global flow resistance. These effects become less important as complexity increases, provided that the network is optimized. A damaged peripheral duct induces a smaller penalty than a damaged duct that is situated close to the center of the network. In summary, optimized complex flow structures are robust. Loops are an attractive design feature for maintaining a high level of global performance when the structure experiences local damage.
Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Seth Lloyd, Adrian Bejan, Charles Bennett, Gian Paolo Beretta, Howard Butler, Lyndsay Gordon, Miroslav Grmela, Elias P. Gyftopoulos, George N. Hatsopoulos, David Jou, Signe Kjelstrup, Noam Lior, Sam Miller, Miguel Rubi, Eric D. Schneider, Dusan P. Sekulic, Zhuomin Zhang; Discussion on "Frontiers of the Second Law". AIP Conf. Proc. 11 August 2008; 1033 (1): 253–261. https://doi.org/10.1063/1.2979039 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search
