Publications

The fundamental question in heat transfer engineering is to determine the relationship between the heat transfer rate and the driving temperature difference. In nature, many saturated porous media interact thermally with one another, and with solid surfaces that...

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%.

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.

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.

Technical Briefs The “Heatline” Visualization of Convective Heat Transfer S. Kimura, S. Kimura Department of Mechanical Engineering, University of Colorado, Boulder, Colo. 80309 Search for other works by this author on: This Site PubMed Google Scholar A. Bejan A. Bejan Department of Mechanical Engineering, University of Colorado, Boulder, Colo. 80309 Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information S. Kimura Department of Mechanical Engineering, University of Colorado, Boulder, Colo. 80309 A. Bejan Department of Mechanical Engineering, University of Colorado, Boulder, Colo. 80309 J. Heat Transfer. Nov 1983, 105(4): 916-919 (4 pages) https://doi.org/10.1115/1.3245684 Published Online: November 1, 1983 Article history Received: December 13, 1982 Online: October 20, 2009

This paper describes a two-part study of the time-dependent melting of an enclosed phasechange material heated at a constant rate from the side. The first part describes experimental measurements with n-octadecane conducted in a 74 cm tall enclosure. The heat flux Rayleigh numbers of these experiments are of the order of 1013, and the liquid flow pattern is weakly turbulent. The second part of the study describes the liquid-superheat effect analytically, by means of a ‘matched boundary layers’ solution for the convection regime of the heat transfer and melting process. The predicted overall Nusselt number relationship agrees very well with the empirical correlation based on experiments.

In this chapter we turn our attention to processes of combined (simultaneous) heat and mass transfer that are driven by buoyancy. The density gradients that provide the driving buoyancy force are induced by the combined effects of temperature and species...

In this paper, we optimize the performance of several classes of simple flow systems consisting of T- and Y-shaped assemblies of ducts, channels and streams. In each case, the objective is to identify the geometric configuration that maximizes performance subject to several global constraints. Maximum thermodynamic performance is achieved by minimization of the entropy generated in the assemblies. The boundary condition is fixed temperature of the channel wall. The flow is assumed laminar and fully developed. Every geometrical detail of the optimized structure is deduced from the constructal law. Performance evaluation criterion is proposed for evaluation and comparison of the effectiveness of different tree-shaped design heat exchangers. This criterion takes into account and compare the entropy generated in the system with heat transfer performance achieved.

This paper establishes a theoretical framework for the minimization of entropy generation (the waste of exergy, or useful energy) in extended surfaces (fins). The entropy generation rate formula for a general fin is derived first. Based on this general result, analytical methods and graphic results are developed for selecting the optimum dimensions of pin fins, rectangular plate fins, plate fins with trapezoidal cross section, and triangular plate fins with rectangular cross section.

As an alternative to the mechanistic point of view expressed in Carathe´odory’s axioms, it is shown that the laws and concepts of thermodynamics are covered also by two statements made from a purely heat transfer perspective: Axiom I′—The heat transfer is the same in all zero-work processes that take a system from a given initial state to a given final state. Axiom II′—In the immediate neighborhood of every state of a system there are other states that cannot be reached from the first via a zero-work process. The primary concepts of this formulation are heat transfer, temperature, entropy, and zero-work boundary. Axiom I′ is used to define the property “energy,” and to deduce the secondary (derived) concept of “work transfer.” Axiom II′ is used to define the thermodynamic properties of “volume” and “pressure.” In this new heat transfer-based scheme, the analog of the Kelvin–Planck statement of the second law is: “∮δW < 0 is impossible” for an integral number of cycles executed by a closed system while in communication with no more than one pressure reservoir.

Nature abounds in examples of evolutionary designs (bio and non-bio) that evolve freely into configurations that provide easier and greater access for movement. The present article considers three seemingly unrelated phenomena that appear to obstruct flow: stick–slip friction, animal jump, and earthquake. The analysis is based on simple models of rhythmic energy store & release motion. In each case, the rhythm is the sole degree of freedom. The analyses show that stick–slip friction facilitates movement because the coefficient of static friction is greater than the coefficient of sliding friction. Next, all forms of animal locomotion under gravity consist of cycles of energy storage (jump to a height) and energy release (forward fall). The rhythm of the cycle is natural such that the forward advance of the animal is economical. Finally, the onset of the earthquake is modeled the same way, as shear stresses at the rock-on-rock interface, which are matched by bending stresses in the bent 'blades' of rock contained between fissures perpendicular to the interface. In sum, naturally evolved store & release rhythm facilitates the movement, contrary to the commonly held impression.

here we explain a much avoided phenomenon in the evolution of speed sports for men and women: The world records in running tend to be set by black athletes and in swimming by white athletes.We show that this phenomenon is predictable from physics.locomotion is a 'falling-forward' cycle, in which body mass falls forward and then rises again.mass that falls from a higher altitude falls faster, down and forward.In running, the altitude (l 1 ) is set by the position of the center of mass above the ground.In swimming, the altitude is set by the upper body rising above the water, and it is proportional to h -l 1 , where h is the height of the athlete.The anthropometric literature shows that the center of mass in blacks is 3 percent higher above the ground than in whites.This means that blacks hold a 1.5 percent speed advantage in running, and whites hold a 1.5 percent speed advantage in swimming.among athletes of the same height asians are even more favored than whites in swimming but they are not setting records because they are not as tall.