901 publications from this institution
movement on earth is effected by bodies (e.g.river channels, animals, vehicles) of seemingly random scales, large and small.here we use the constructal law and the design of 'distributed energy systems' to show that the large must be few and the small many, in particular proportions that are required for greater access for movement on areas.First, we demonstrate that mass movement per kilogram moved and kilometer traveled requires less fuel on larger vehicles.The thermodynamics basis of this is the same as for the effect of size on the efficiency of motors, vascular flow architectures and river basins.The same principle dictates that on every vehicle the motor mass must scale with the structural mass, and with the total mass.In addition, larger masses must move on areas to greater distances, and a characteristic number of smaller masses must be allocated to a larger mass to travel, on the same area element.
In the examples of forced and natural convection discussed until now, the fluid that flowed through the pores did not experience a change of phase, no matter how intense the heating or cooling effect. In the present chapter we turn our attention to situations in...
The constructal law of design evolution is the law of physics that expresses the natural tendency of all flow systems, bio and nonbio, to morph into configurations that provide greater flow access over time. River basins, animal locomotion and migratory routes, snowflakes, and turbulence structure illustrate this tendency of design occurrence and evolution over time. The movement and persistence of human life on the landscape (people, goods, construction, and mining) also evolves in accord with the constructal law. Each of us belongs to the “human and machine” species, the evolving design that is better known as technology evolution. In this chapter, I illustrate the technology evolution phenomenon by showing that larger flow components (organs) belong on larger vehicles and animals and that the time arrow of the constructal law points toward smaller sizes over time (miniaturization). This evolutionary direction is further illustrated by the evolution of cooling technology for high-density heat transfer, from natural convection to forced convection and pure conduction, Fourier and non-Fourier. Tree-shaped flow architectures emerged from the same constructal-law tendency when the flow connects one point with an infinity of points (area and volume). At bottom, all technology evolution is about facilitating the movement of the human and machine species on the world's map. This is why the more advanced groups consume proportionally more fuel and why both wealth and fuel consumption continue to rise naturally.
This paper reports a numerical study of two-dimensional natural convection in a horizontal porous layer heated from below and saturated with cold water. The density maximum of water at 3.98°C and atmospheric pressure occurs inside the layer, as the top surface is maintained at 0°C and the bottom surface is varied from 4 to 8°C. Three separate series of numerical simulations document the effect of Rayleigh number, bottom surface temperature, and horizontal length of the porous layer on the overall heat transfer rate vertically through the layer. The range of these numerical experiments is 200 < Ra p < 10000, 0.167 < H/L < 1 and °C < T H < 8°C, where Ra p , H/L and T H are the Darcy-modified Rayleigh number for a fluid with density maximum, the geometric ratio height/length, and the bottom wall temperature. The numerical results agree with published linear stability results regarding the onset of convection.
In this paper we develop an analytical and graphical formulation of the constructal law of maximization of flow access in systems with heat and fluid flow irreversibilities and freedom to change configuration. The flow system has global performance (e.g., minimization of global flow resistance) and global properties, or constraints (e.g., overall size, and total duct volume). The infinity of possible flow structures occupies a region of the two-dimensional domain of “global performance versus freedom to morph”. This region of “nonequilibrium flow structures” is bounded by a line representing the best flow structures that are possible when the freedom to morph is limited. The best of all such structures are the “equilibrium flow structures”: here the performance level is the highest, and it does not change even though the flow architecture can change with maximum freedom. The universality of this graphical and analytical presentation is illustrated with examples of flow structures from three classes: flow between two points, flow between a circle and its center, and flow between one point and an area. In sum, this paper presents an analytical and graphical formulation of the constructal principle of generation of flow architecture. The place of this new and self-standing principle in the greater framework of thermodynamics is outlined.
Constructal theory is the view that the generation of flow configuration is a physics phenomenon that can be based on a physics principle (the constructal law): “For a finite-size flow system to persist in time (to survive) its configuration must evolve in such a way that it provides an easier access to the currents that flow through it” [A. Bejan, Advanced Engineering Thermodynamics, 2nd ed. (Wiley, New York, 1997); Int. J. Heat Mass Transfer, 40, 799 (1997)]. This principle predicts natural configuration across the board: river basins, turbulence, animal design (allometry, vascularization, locomotion), cracks in solids, dendritic solidification, Earth climate, droplet impact configuration, etc. The same principle yields new designs for electronics, fuel cells, and tree networks for transport of people, goods, and information. This review describes a paradigm that is universally applicable in natural sciences, engineering and social sciences.
No abstract is provided for this article.
This paper reports a fundamental study of laminar natural convection in a rectangular enclosure with heat and mass transfer from the side, when the bouyancy effect is due to density variations caused by either temperature or concentration variations. In the first part of the study scale analysis is used to determine the scales of the flow, temperature and concentration fields in boundary layer flow for all values of Prandtl and Lewis numbers. In particular, scale analysis shows that in the extreme case where the flow is driven by bouyancy due to temperature variations, the ratio of mass transfer rate divided by heat transfer rate scales as Le 1 2 only if (Pr > 1, Le < 1) or (Pr < 1, Sc < 1), and as Le 1 3 if (Pr > 1, Le > 1) or (Pr < 1, Sc > 1). In the second part of the study, the boundary layer scales derived in the first part are used to determine the heat and mass transport characteristics of a vertical slot filled with fluid. Criteria for the existence of distinct thermal and concentration boundary layers in the slot are determined. Numerical solutions for the flow and concentration fields in a slot without distinct thermal boundary layers are reported. These solutions support further the method of scale analysis employed in the first part of the study
In this paper, we review the main advances made by our research group on the heat transfer performance of complex flow architectures embedded in a conducting solid. The immediate applications of this work include the design of ground-coupled heat pumps, seasonal thermal energy storage systems, and district heating and cooling systems. Various configurations are considered: U-shaped ducts with varying spacing between the parallel portions of the U, serpentines with three elbows, and trees with T-shaped and Y-shaped bifurcations. In each case, the volume ratio of fluid to soil is fixed. We found the critical geometric features that allow the heat transfer density of the stream-solid configuration to be the highest. In the case of U-tubes and serpentines, the best spacing between parallel portions is discovered, whereas the vascular designs morph into bifurcations and angles of connection that provide progressively greater heat transfer rate per unit volume. We show that the flow of heat into or out of a solid volume must have an S-shaped history curve that is entirely deterministic. This constructal-design principle unites a wide variety of previously disconnected S-curve phenomena (ground heat storage and retrieval, population growth, cancer, chemical reactions, contaminants, languages, news, information, innovations, technologies, economic activity).
This paper shows that the architecture of a steam generator for a power plant can be deduced on the basis of the constructal law. According to constructal theory, the flow architecture emerges in time such that it provides progressively greater access to its currents. The circulation of water is driven by buoyancy in one large tube (the downcomer) and many parallel smaller tubes (the riser). The total flow volume is fixed. Two flow models are used: single phase liquid in the downcomer and riser, and liquid–vapor mixture in the riser tubes. Features that result from constructal design are: the tube diameters, the number of riser tubes, the water circulation rate, the rate of steam production, and how the flow architecture should change when the operating pressure and the size of the flow system change.
This paper describes a natural language processing system for the task of pneumonia identification. Based on the information extracted from the narrative reports associated with a patient, the task is to identify whether or not the patient is positive for pneumonia.A binary classifier was employed to identify pneumonia from a dataset of multiple types of clinical notes created for 426 patients during their stay in the intensive care unit. For this purpose, three types of features were considered: (1) word n-grams, (2) Unified Medical Language System (UMLS) concepts, and (3) assertion values associated with pneumonia expressions. System performance was greatly increased by a feature selection approach which uses statistical significance testing to rank features based on their association with the two categories of pneumonia identification.Besides testing our system on the entire cohort of 426 patients (unrestricted dataset), we also used a smaller subset of 236 patients (restricted dataset). The performance of the system was compared with the results of a baseline previously proposed for these two datasets. The best results achieved by the system (85.71 and 81.67 F1-measure) are significantly better than the baseline results (50.70 and 49.10 F1-measure) on the restricted and unrestricted datasets, respectively.Using a statistical feature selection approach that allows the feature extractor to consider only the most informative features from the feature space significantly improves the performance over a baseline that uses all the features from the same feature space. Extracting the assertion value for pneumonia expressions further improves the system performance.
This technical note develops an analytical result for heat transfer by laminar free convection in a long horizontal parallel-plate channel connecting two reservoirs containing the same fluid but kept at different temperatures. The analysis is based on the integral method. The Nusselt number result is presented in chart form in terms of the Rayleigh number based on height, Ra, and the height/length aspect ratio, h/L.
This article describes the concept of engineering science and its different principles. Engineering science consists of few principles on which nature is founded: the laws of mechanics, thermodynamics, and design because these principles lead us straight, not on a blind and crooked path of trial and error. These few principles unite the animate systems with the inanimate systems, which are much older on Earth and unite the ‘natural’ with the ‘artificial.’ The article also focuses on linking engineering with science and shows through numerous examples that engineering and science are one. The paper shows that science is a story, and the better story is the better science, and science with engineering is a much better story than science without engineering. The value of science is a lot subtler, and it is monumental. There have been several mechanical engineers whose works have had a significant impact on science that most academics think these men were physicists and not engineers.
This article is about novel applications of computational heat transfer and fluid dynamics: the optimization and design of complex tree-shaped flow structures for cooling high-density heat-generating volumes (e.g., electronics). The focus is on computational cost, and how to reduce it by devising effective strategies for identifying paths that lead to the optimal complex flow structure. The method is illustrated by considering dendritic architectures that connect with laminar fluid flow the center of a circle with points distributed equidistantly on the circle. Optimal architectures are pursued numerically based on several methods: the optimization of every geometric detail of the complex structure, the minimization of every duct length, and the optimization of every angle of bifurcation. It is shown that strategy leads to dramatic increases in optimization speed, and provides an effective albeit approximate description of the optimal complex flow structure.
No abstract is provided for this article.
Physics is concise, simple, unambiguous, and constantly improving. Yet, confusion reigns in the field especially with respect to complexity and the second law of thermodynamics. In this paper, we step back and take a look at these notions—their meaning and definition—on the background provided by nature and thermodynamics. We review the central concepts and words that underpin the physics of evolutionary design today: information, knowledge, evolution, change, arrow of time, pattern, organization, drawings, complexity, fractal dimension, object, icon, model, empiricism, theory, disorder, second law, the “any” system in thermodynamics, morphing freely, and the constructal law. We show, for example, that information is not knowledge, fractal dimension is not a measure of complexity, and pattern is not a live flow architecture. Drawings, as physical means to facilitate the flow of knowledge, are subject to the natural tendency toward design evolution. Complexity, organization, and evolution in nature are most powerful and useful when pursued as a discipline, with precise terms, rules, and principles.
This paper considers the question of whether the optimum phase-change temperature for maximum exergy storage is universally equal to the geometric mean of the heat source and environment temperature, Tm=(T∞Te)1/2. The study consists of three parts. The first deals with the conduction-melting process, and shows that the optimum melting temperature is generally greater than the geometric mean of the source and environment temperatures. The second part covers the conduction-solidification process, and concludes that the irreversibility of solidification decreases monotonically as the phase-change temperature increases. The third part treats the complete cycle of melting (storage) followed by solidification (retrieval), and demonstrates that the optimum phase-change temperature is greater than the optimum temperature of the melting process alone.
No abstract is provided for this article.
