This paper reports the thermodynamic optimization (or entropy generation minimization) of a heat-driven refrigeration plant, that is, a refrigerator without work input, which is driven by a heat source. The treatment accounts for the heat transfer irreversibilities of the three heat exchangers, and for the finiteness of the total heat-exchanger inventory. The operating conditions for maximum refrigeration rate are determined. It is shown that the heat-exchanger inventory must be divided optimally between the three heat exchangers. For example, half of the inventory must be placed in the heat exchanger used to reject heat to the ambient. The maximum refrigeration rate per unit of total heat exchanger inventory is reported. These thermodynamic optimization principles are then applied to a refrigerator driven by heat transfer from a solar collector.
This article unveils the geometric characteristics of boats with sails of many sizes, covering the range 10 2 –10 5 kg. Data from one hundred boat models are collected and tabulated. The data show distinct trends of convergent evolution across the entire range of sizes, namely: (i) the proportionality between beam and draft, (ii) the proportionality between overall boat length and beam, and (iii) the proportionality between mast height and overall boat length. The review shows that the geometric aspect ratios (i)–(iii) are predictable from the physics of evolution toward architectures that offer greater flow access through the medium.
WithEvolution freedomFreedom comes evolutionEvolution, and with evolutionEvolution come all these visible things, images, designsDesign, complexityComplexity, diversityDiversity, hierarchyHierarchy, sizeSize, free choices, and the universality of economies of...
This is a study of the flow driven by the buoyancy effect associated with the non-uniform volumetric absorption of a spatially uniform flux of thermal radiation that impinges on a body of fluid. The nonuniform absorption of radiation is due to the presence of regions of relative turbidity (coloring, suspension of particulates, algae) that alter the optical properties of the fluid. Focusing on the earliest stages of buoyancy-driven flow in the immediate vicinity of a relatively absorptive region, this study shows that the flow acquires a double-counterflow structure and that its effect is to rearrange the fluid so that increasingly warmer layers are positioned closer to the free surface. Analytically, the phenomenon is investigated on the basis of scale analysis and an asymptotic solution that is valid for vanishingly small times or Grashof numbers. Numerical experiments performed in a shallow two-dimensional layer confirm the flow structure and scaling trends anticipated theoretically.
'The Constructal Law in Nature and Society' published in 'Constructal Theory of Social Dynamics'
This article outlines the basic rules and promise of two of the simplest methods for solving problems of convection in porous media. First, scale analysis is the method that produces order-of-magnitude results and trends (scaling laws) for concrete and applicable results such as heat transfer rates, flow rates, and time intervals. Scale analysis also reveals the correct dimensionless form in which to present more exact results produced by more complicated methods. Second, the intersection of asymptotes method identifies the correct flow configuration (e.g. Bénard convection in a porous medium) by intersecting the two extremes in which the flow may exist: the many cells limit, and the few plumes limit. Every important feature of the flow and its transport characteristics is found at the intersection, i.e. at the point where the two extremes compete and find themselves in balance. The intersection is also the flow configuration that minimizes the global resistance to heat transfer through the system. This is an example of the constructal principle of deducing flow patterns by optimizing the flow geometry for minimal global resistance. The article stresses the importance of trying the simplest method first, and the researcher's freedom to choose the appropriate problem solving method. Copyright © 2003 John Wiley & Sons, Ltd.
This paper describes the most basic thermodynamic aspects of the process of energy storage by melting of a phase change material when the energy source is a stream of hot single-phase fluid. The first part of the paper considers the melting process ruled by pure conduction across the liquid phase, and the second part deals with the quasi-steady melting dominated by natural convection. The paper establishes the relationship between the total irreversibility of the melting process and design parameters such as the number of heat transfer units of the heat exchanger placed between the energy source and the phase change material, the duration of the melting process, and the position of the energy storage process on the absolute temperature scale. It is shown that the exergy transfer to the melting material is maximized when the melting temperature (Tm) equals the geometric average of the environment temperature (Te) and the temperature of the energy source (T∞), in other words when Tm=(TeT∞)1/2. This conclusion holds for both conduction-dominated melting and convection-dominated melting.
The emerging concept of smart buildings, which requires the incorporation of sensors and big data (BD) and utilizes artificial intelligence (AI), promises to usher in a new age of urban energy efficiency. By using AI technologies in smart buildings, energy consumption can be reduced through better control, improved reliability, and automation. This paper is an in-depth review of recent studies on the application of artificial intelligence (AI) technologies in smart buildings through the concept of a building management system (BMS) and demand response programs (DRPs). In addition to elaborating on the principles and applications of the AI-based modeling approaches widely used in building energy use prediction, an evaluation framework is introduced and used for assessing the recent research conducted in this field and across the major AI domains, including energy, comfort, design, and maintenance. Finally, the paper includes a discussion on the open challenges and future directions of research on the application of AI in smart buildings.
We are the human & machine species. The homo is just the inner part. The evolution of the human & machine species is oriented in time from the naked man to the man with progressively more powerful add-ons (artifacts, contrivances, devices, machines, science). In evolution, the flow system morphs with freedom in the discernible direction identified as the constructal law. In all evolutionary designs, what works is kept
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 Adrian Bejan; Engineering advances on finite‐time thermodynamics. American Journal of Physics 1 January 1994; 62 (1): 11–12. https://doi.org/10.1119/1.17730 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 ContentAmerican Association of Physics TeachersAmerican Journal of Physics Search Advanced Search |Citation Search
The literature reviewed in this article shows that the evolution of vehicles is in line with the evolution of animal locomotion and that it is predictable from the constructal law of design and evolution in nature. The evolution of ships and airplanes illustrates the evolutionary design of the “human-and-machine species” as it moves and spreads on Earth: farther, faster, more efficiently, and with greater lasting power (sustainability). Every vehicle size has its design. The bigger vehicle is not a magnified facsimile of the smaller. The size fraction that the lifting organs occupy in the overall vehicle increases with the body size. Every vehicle size has its niche, the supporting territory, and population to which it belongs. All the designs of movement on the globe evolve. Vehicles do not evolve by themselves; they evolve hand in glove with the humans who design and use them. The result is hierarchy, and it is why hierarchy is natural and unavoidable. We see it in geophysical movement (river basins), animal movement (food chain), human social movement (global air and maritime traffic), and everywhere else. The appearance of a new hierarchical design of movement on earth does not eliminate the existing hierarchical designs of movement. The new hierarchy joins the old, and what works is kept. No evolving system deviates from the features dictated by the law of physics of evolution in nature.
Grid-shaped and tree-shaped flow architectures are being generated for use in vascularized materials with multiple functionality (self-healing, self-cooling, etc), based on the principle of the constructal law of evolutionary increase of flow access through the generation of better flowing configurations (designs). Here we investigate systematically the advantages of endowing the complex flow architecture with more freedom to morph. Four ways to increase design freedom are explored: multi-scale grids (one, two, three and four diameter sizes), multi-shape loops (square, triangular, hexagonal, rhombic), multi-shape bodies (hexagonal, square, rhombic) and vascularization with grids versus trees. We show that significant gains in global flow access are achieved as the number of optimized channel diameters increases. The most promising combinations of body and loop shapes are hexagonal bodies with triangular loops and square bodies with square loops. The tree-shaped architecture outperforms the grid, but it is recommendable only for stressed bodies in which the most likely location of the cracks is known ahead of time. The effect of body size on the global performance of vascularized multi-scale and multi-shape materials is documented. Diminishing returns and increasing robustness set in as the complexity of the optimized flow architectures increases.
Shape and Thermodynamics is a two-day international Workshop focused on the Constructal Theory of generation of configuration in nature and engineering. From the early developments related to tree configurations for the cooling of electronics, today Constructal theory is being applied to conceptual design of transportation net-works, river basins, living bodies, building materials and many other flow systems. Constructal theory is also enriching thermo-dynamics, from basic theory to design and optimization. This theory approaches design science, with the generation of configuration regarded as a phenomenon of all physics, based on principle (the Constructal law). For example, Constructal Theory contributes to the evolution of fuel cells, in the design of cooling channels, the optimal feeding of reactants, etc. Important applications are also found in the design of heat exchangers, district heating networks, etc. The growing scientific literature on Constructal Theory has an important Italian component, although further dissemination is timely. Moreover, the relation with other thermodynamic research areas deserves to be explored.
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...
Most of the studies of convection in porous media published before 1970 were motivated by geophysical applications, and many published since have geophysical ramifications; see, for example, the reviews by Cheng (1978, 1985b). On the other hand, geothermal reservoir...
This paper describes an integral (macroscopic) approach to the evaluation and maximization of performance in the design of networks for the distribution of electric power. The method recognizes the hierarchical structure of tree shaped networks and accounts for all the consumption nodes, links (lines) and loads carried by each line. The lines that carry the same load form one group. The total length of the lines belonging to one group is calculated. The total length of all the lines is the sum of the total lengths calculated for each group. This analysis makes it possible to represent one network as a curve in the load–length plane. Next, the moment of the load at one consumption node is defined as the load times the direct distance from the source to the node. The global load moment is the sum of all the individual load moments. The global load moment is proportional to the area trapped above the load–length curve of the network. It is shown that this area must be minimized in order to minimize the discounted total cost of the network. Six competing distribution networks are compared on this integral basis. Networks that are tree shaped and sufficiently complex perform at nearly the same (high) level. The robustness exhibited by tree shaped power distribution networks is similar to the robustness of other tree flow structures (fluid, heat, goods, people) in animate, inanimate and engineered flow systems in accordance with constructal theory.
DesignsDesign (images with meaning) areNature and power everywhere, around us and inside us. Best known are the tree shaped flowFlow structures of the river basinsRiver basins, humanHumans lungs, lightning, vascular tissue, urban traffic, snowflakes, riverRivers...
This paper considers the basic thermal design problem of cooling or heating an object using the minimum amount of working fluid. It is shown analytically that if the duration of the cooling or heating process is fixed, then there exists a unique operating regime (flowrate-time function) which insures the minimum consumption of working fluid. The optimum flowrate is proportional to ( U Cp ) 1 2 , where U is the overall heat transfer coefficient and C p is the specific heat of the working fluid ; the optimum flowrate changes with time as ( U Cp ) 1 2 varies with the temperature of the system. Numerical examples of cooldown and energy storage processes show that the implementation of this optimum operating regime can lead to significant savings in working fluid.
