Showing papers on "Constructal law published in 2008"
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01 Jan 2008TL;DR: Constructal theory is the view that the generation of "designedness" in nature is a universal (physics) phenomenon that can be based on principle (the constructal law): "For a finite-size flow system to persist in time (to live) its configuration must change in time so that it provides greater and greater access to its currents" as discussed by the authors.
Abstract: Constructal theory is the view that the generation of “designedness” in nature is a universal (physics) phenomenon that can be based on principle (the constructal law): “For a finite-size flow system to persist in time (to live) its configuration must change in time so that it provides greater and greater access to its currents”. This principle predicts natural form across the board, from river basins to animal design, engineering and social dynamics. In this introduction to the theory we show examples of vascular designs at large and small scales and multi-objective flow configurations.
761 citations
TL;DR: It is shown that there exists an optimal ratio of leaf volume divided by total tree volume, trees of the same size must have a larger wood volume fraction in windy climates, and larger trees must pack more wood per unit of tree volume than smaller trees.
113 citations
TL;DR: It has been shown that small deviations from the minimum mass optimum can be tolerated, but large variations could be expected to produce a punitive and rapidly increasing mass penalty.
Abstract: A biomimetic analysis is presented in which an expression for the optimum vessel diameter for the design of minimum mass branching or vascular networks in engineering applications is derived. Agreement with constructal theory is shown. A simple design case is illustrated and application to more complex cases with branching networks of several generations discussed. The analysis is also extended into the turbulent flow regime, giving an optimization tool with considerable utility in the design of fluid distribution systems. The distribution of vessel lengths in different generations was also found to be a useful design variable. Integrating a network into a structure is also discussed. Where it is necessary to adopt a non-optimum vessel diameter for structural integration, it has been shown that small deviations from the minimum mass optimum can be tolerated, but large variations could be expected to produce a punitive and rapidly increasing mass penalty.
89 citations
TL;DR: In this article, the authors modify the Pennes model by taking into account the thermal relaxation time of biological tissue, and employ the Maxwell-Cattaneo thermal flux law, in conjunction with the fourth power law, to model the effects of high thermal radiation on such skin.
84 citations
TL;DR: In order to solve the key issue of the link between the micro-scale and the macro-scale, multi-scale methodology such as fractal and constructal approaches for the design optimization of μHXs are introduced.
Abstract: In this paper, a literature review of the recent research advances and applications of microchannel (from 1 μm to 1 mm) heat exchangers (μHXs) is presented. After a brief introduction of basic definitions, the advantages and limitations of μHXs are summarized with examples. Recent applications of these exchangers are reported. Although much in-depth research work still needs to be done, great potential has already been shown for large-scale applications of μHXs in process intensification of various industrial areas. Moreover, in order to solve the key issue of the link between the micro-scale and the macro-scale, multi-scale methodology such as fractal and constructal approaches for the design optimization of μHXs are introduced. Finally, the concept of constructal heat exchanger is presented.
82 citations
TL;DR: In this article, a new physical quantity, entransy, has been identified as a basis for optimizing heat transfer processes in terms of the analogy between heat and electrical conduction, and all of the heat conduction constructal problems may be re-optimized based on it.
Abstract: The 'volume to point' heat conduction problem, which can be described as to how to determine the optimal distribution of high conductivity material through the given volume such that the heat generated at every point is transferred most effectively to its boundary, has became the focus of attention in the current constructal theory literature. In general, the minimization of the maximum temperature difference in the volume is taken as the optimization objective. A new physical quantity, entransy, has been identified as a basis for optimizing heat transfer processes in terms of the analogy between heat and electrical conduction recently. Heat transfer analyses show that the entransy of an object describes its heat transfer ability, just as the electrical energy in a capacitor describes its charge transfer ability. Entransy dissipation occurs during heat transfer processes, as a measure of the heat transfer irreversibility with the dissipation related thermal resistance. By taking equivalent thermal resistance (it corresponds to the mean temperature difference), which reflects the average heat conduction effect and is defined based on entransy dissipation, as an optimization objective, the 'volume to point' constructal problem is re-analysed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the elemental area and the first order construct assembly, when the thermal current density in the high conductive link is linear with the length, the optimized shapes of assembly based on the minimization of entransy dissipation are the same as those based on minimization of the maximum temperature difference, and the mean temperature difference is 2/3 of the maximum temperature difference. For the second and higher order construct assemblies, the thermal current densities in the high conductive link are not linear with the length, and the optimized shapes of the assembly based on the minimization of entransy dissipation are different from those based on the minimization of the maximum temperature difference. For the same parameters, the constructs based on minimization of entransy dissipation and the constructs based on minimization of the maximum temperature difference are compared, and the results show that the constructs based on entransy dissipation can decrease the mean temperature difference better than the constructs based on minimization of the maximum temperature difference and therefore can improve the conductive ability greatly. Because the idea of entransy describes the heat transfer ability more suitably, all of the heat conduction constructal problems may be re-optimized based on it.
80 citations
TL;DR: In this article, a volume-to-point constructal problem of how to discharge the heat generated in a fixed volume to a heat sink on the border through relatively high conductive link is re-analyzed and re-optimized.
Abstract: By taking equivalent thermal resistance, which reflects the average heat conduction effect and is defined based on entransy dissipation, as optimization objective, the “volume to point” constructal problem of how to discharge the heat generated in a fixed volume to a heat sink on the border through relatively high conductive link is re-analyzed and re-optimized in this paper. The constructal shape of the control volume with the best average heat conduction effect is deduced. For the elemental area and the first order construct assembly, when the thermal current density in the high conductive link is linear with the length, the optimized shapes of assemble based on the minimization of entransy dissipation are the same as those based on minimization of maximum temperature difference, and the mean temperature difference is 2/3 of the maximum temperature difference. For the second and higher order construct assemblies, the thermal current densities in the high conductive link are not linear with the length, and the optimized shapes of assemble based on the minimization of entransy dissipation are different from those based on minimization of maximum temperature difference. For the same parameters, the constructs based on minimization of entransy dissipation and the constructs based on minimization of maximum temperature difference are compared, and the results show that the constructs based on entransy dissipation can decrease the mean temperature difference better than the constructs based on minimization of maximum temperature difference. But with the increase of the number of the order, the mean temperature difference does not always decrease, and there exist some fluctuations. Because the idea of entransy describes the heat transfer ability more suitably, all of the heat conduction constructal problems may be re-optimized based on it.
54 citations
TL;DR: In this article, the effects of constructal distributors or collectors, built on a binary pattern of pores, on flow equidistribution in a multi-channel heat exchanger were examined experimentally.
Abstract: This paper examines experimentally the effects of constructal distributors or collectors, built on a binary pattern of pores, on flow equidistribution in a multi-channel heat exchanger. Thermal performance and pressure drop have been determined with different assembly configurations of constructal distributors, conventional pyramid distributors and a mini crossflow heat exchanger (MCHE). Experimental results show that the integration of constructal distributors/collectors could homogenize the fluid flow distribution and consequently lead to a better thermal performance of the MCHE, but it also results in higher pressure drops. Among all tested assembly configurations, the configuration where the inlet is equipped with a conventional pyramid distributor, and the outlet is equipped with a constructal collector (Apec) shows a relatively better thermal performance as well as low pressure drops under experimental conditions considered.
53 citations
TL;DR: In this paper, the flow distribution behavior of a plate-type constructal flow distributor, which has one inlet and 16 outlets and is designed according to constructal theory to achieve uniform flow distribution with smallest energy dissipation and shortest residence time, is investigated by experiments.
51 citations
TL;DR: In this paper, a dual-domain model is applied to simulate the heterogeneous porous media embedded with a constructal tree network based on the fractal distribution of pore space and tortuosity nature of flow paths.
Abstract: In this paper, an analysis of the radial flow in the heterogeneous porous media based on fractal and constructal tree networks is presented. A dual-domain model is applied to simulate the heterogeneous porous media embedded with a constructal tree network based on the fractal distribution of pore space and tortuosity nature of flow paths. The analytical expressions for seepage velocity, pressure drop, local and global permeability of the network and binary system are derived, and the transport properties for the optimal branching structure are discussed. Notable is that the global permeability ( K n ) of the network and the volume fraction ( f n ) occupied by the network exhibit linear scaling law with the fractal dimension ( D p ) of channel diameter by log K n ∼ 0.46 D p and log f n ∼ 1.03 D p , respectively. Our analytical results are in good agreement with the available numerical results for steady-state soil vapor extraction and indicate that the fractal dimension for pore space has significant effect on the permeable properties of the media. The proposed dual-domain model may capture the characteristics of heterogeneous porous media and help understanding the transport mechanisms of the radial flow in the media.
47 citations
TL;DR: In this paper, the design and analysis of a multi-block heat exchanger has been carried out by applying the concept of constructal theory proposed by Bejan, which works on the principle of developing laminar flow in each block carefully designed to avoid fully developed heat transfer coefficient.
TL;DR: In this paper, a numerical and experimental study on flow maldistribution and heat transfer intensification in a mini heat exchanger with constructal distributor/collector integrated is presented.
Abstract: This article reports a numerical and experimental study on flow maldistribution and heat transfer intensification in a mini heat exchanger with constructal distributor/collector integrated. The flow distribution characteristics of the constructal component functioning as a fluid distributor or as a fluid collector have been investigated and compared using computational fluid dynamics simulations. An experimental setup is designed and constructed for thermal and hydraulic performances tests. The effects of various assembly configurations on heat transfer characteristics and pressure drops are discussed. The results indicate that the integration of one constructal collector at the outlet of the heat exchanger can achieve almost uniform flow distribution and consequently better intensify the heat transfer. It is also the most advantageous configuration based on a balanced consideration of heat transfer intensification and pump power consumption under the investigation conditions.
TL;DR: In this article, a statistical and dynamical interpretation for the entropy due to irreversibility is proposed as a foundation of the constructal theory, based on the thought that flow architecture is a consequence of a principle of maximization of flow access, in time, and in flow configuration that is free to be realised.
Abstract: The constructal theory is based on the thought that flow architecture is a consequence of a principle of maximization of flow access, in time, and in flow configuration that is free to be realised. The principle of maxima for the variation of the entropy due to irreversibility represents a general principle of investigation for the stability of open systems, by which it is possible to predict some macroscopic shapes, originated by the spatial organisation, in Nature, both in living and in non-living objects. Its statistical meaning has recently been introduced. Here a statistical and dynamical interpretation for the entropy due to irreversibility is proposed as a foundation of the constructal theory.
TL;DR: In this paper, the authors rely on constructal theory to show that the flow architecture that provides the greatest access from point to volume and from volume to point is the three-dimensional compounding of trees matched canopy to canopy.
Abstract: Nature shows that fluids bathe the animal body as trees matched canopy to canopy. The entering streams invade the body as river deltas and the reconstituted streams sweep and exit the body as river basins. Why should this be so? Why is animal vascularization not based on arrays of parallel channels, as in modern heat exchangers? In this paper, we rely on constructal theory to show that the flow architecture that provides greatest access from point to volume and from volume to point is the three-dimensional compounding of trees matched canopy to canopy. This three-dimensional tree architecture is deduced, not assumed. Its flow performance is evaluated at every step relative to the performance of equivalent architectures with parallel channels. This paper also shows that the dendritic design must become more complex (with more levels of branching) as the volume inhabited by the flow design increases. The transition from designs with p branching levels to p+1 levels occurs abruptly as the available flow volu...
TL;DR: In this article, an entropy generation minimization for heat and mass transfer process in a solid-gas reactor is carried out based on constructal theory by using triangular elemental area. But the results show that smaller entropy generation can be obtained when the optimization for a given volume is carried on the basis of triangular elements than those obtained on the base of rectangular elements.
Abstract: Entropy generation minimization for heat and mass transfer process in a solid-gas reactor is carried out based on constructal theory by using triangular elemental area. The aspect ratio of the triangular elemental area is optimized under constraint conditions. A number of optimal triangular elements are assembled to a new large rectangular area, which is optimised again. The procedure is repeated until the control-volume is covered, and the complete analytical results are obtained. The effects of some parameters on minimum entropy generation are analysed by numerical examples. The results show that smaller entropy generation can be obtained when the optimization for a given volume is carried out on the basis of triangular elements than those obtained on the basis of rectangular elements.
TL;DR: In this paper, a review of 14 different constructal theory applications involving tree-shaped flow networks is presented, with the purpose to check whether the increase in branching of tree shaped flow networks leads to increased flow performance or not.
TL;DR: In this paper, the authors take a fresh look at the generation of architecture of solar energy-based systems based on the constructal theory and investigate three different systems: a shading system to control the incoming of solar radiation during the summer and the winter, a bundle of pipes to warm a room, and a distillation system integrated in a roof.
01 Jan 2008
TL;DR: In this paper, a tree-shaped (dendritic) flow architecture was proposed to achieve volumetric cooling, selfhealing, enhanced apparent thermal conductivity, and mechanical strength.
Abstract: In this paper we use two developments to illustrate our progress in “design with constructal theory” [1]. The first is the development of smart materials with embedded vasculatures that provide multiple functionality: volumetric cooling, selfhealing, enhanced apparent (effective) thermal conductivity, and mechanical strength. Vascularization is achieved by using tree-shaped (dendritic) flow architectures. We show that as length scales become smaller, dendritic vascularization provides dramatically superior volumetric bathing than the use of bundles of parallel microchannels. A novel dendritic architecture has trees that alternate with upside down trees. In addition to flow access to the entire volume, trees offer improved robustness in flow operation. The second development is the distributing of energy systems over a given territory. The distribution of heating is used as an example. The architecture emerges from the balancing of the losses concentrated in the production centers and the losses distributed along the conduits that distribute and collect every thing that flows on the landscape. In sum, flow architectures are derived from principle, in accordance with constructal theory, not by mimicking nature.
TL;DR: Both the scaling laws and self-similarity emerge from the underlying dynamics, together with the purpose of optimizing flows of people and goods in time, as predicted by the Constructal Law.
Abstract: The distributions of street lengths and nodes follow inverse-power distribution laws. That means that the smaller the network components, the more numerous they have to be. In addition, street networks show geometrical self-similarities over a range of scales. Based on these features many authors claim that street networks are fractal in nature. What we show here is that both the scaling laws and self-similarity emerge from the underlying dynamics, together with the purpose of optimizing flows of people and goods in time, as predicted by the Constructal Law. The results seem to corroborate the prediction that cities’ fractal dimension approaches 2 as they develop and become more complex. c 2007 Elsevier B.V. All rights reserved.
TL;DR: The reported research is aimed at delivering a possible, constructal solution that is based on a minimumredundant, scalable, reconfigurable topology that helps increasing the grid immunity to faults.
Abstract: Superior, scalable grid topology that may provide for higher quality of service, survivorship capacity, and reconfiguration capability is a feature of modern grid architecture. The reported research is aimed at delivering a possible, constructal solution that is based on a minimumredundant, scalable, reconfigurable topology that helps increasing the grid immunity to faults. We assume that a tree network serves nodes of consumption that are evenly distributed throughout the territory. All nodes are equally important and network survivability means delivering electrical energy to as many consumers as possible. The models and loads estimation is based on the load momentum method.
01 Jan 2008
TL;DR: In this paper, a staged compression with intermediate refrigeration is considered and the principle of equal distribution of irreversibility, which is one of the aspects of the Constructal Law, is demonstrated.
Abstract: A compressor with heat recovery is thermodynamically analyzed from a second-law point of view, in terms of entropy generation minimization. The unit is optimized, accounting for heat exchange and pressure loss irreversibility, and the maximum output is found, in terms of combined mechanical and thermal energy, for a given input energy at the compressor shaft. This analysis is intended as a part of the thermal optimization on a CAES TES (Compressed Air Energy Storage with Thermal Energy Storage) plant. The latter, if an artificial reservoir is used for compressed air, requires high operating pressure. Hence, this work focuses on a staged compression with intermediate refrigeration. The principle of equal distribution of irreversibility, which is one of the aspects of the “Constructal Law” is then demonstrated. From these findings, a good approximation can be found for the optimal configuration of a complex multi-stage system
01 Jan 2008
TL;DR: Shape and Thermodynamics as discussed by the authors is a two-day international workshop focused on the Constructal Theory of generation of configuration in nature and engineering, from 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.
Abstract: 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 "as 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.
Website: Shape and Thermodinamics
01 Jan 2008
TL;DR: In this article, the authors outline progress on developing flow architectures for a new class of smart materials: composites with vascular channels that provide volumetric flowing (bathing) and cooling.
Abstract: Constructal theory complements the analysis of thermodynamic systems by focusing on the flow configuration of the system, and on the relationship between configuration (design) and global performance. The design progress made in this emerging field is reviewed in a new book [1]. In this paper we outline our progress on developing flow architectures for a new class of smart materials: composites with vascular channels that provide volumetric flowing (bathing) and cooling.Copyright © 2008 by ASME
TL;DR: In this article, tree-shaped (dendritic) and grid-shaped flow architectures are used to achieve better volumetric bathing and transport properties than the use of bundles of parallel microchannels.
Abstract: Here we draw attention to the development of smart materials with embedded vasculatures that provide multiple functionality: volumetric cooling, self-healing, mechanical strength, etc. Vascularization is achieved by using tree-shaped (dendritic) and grid-shaped flow architectures. As length scales become smaller, dendritic vascularization provides dramatically superior volumetric bathing and transport properties than the use of bundles of parallel microchannels. Embedded grids of channels provide substantially better volumetric bathing when the channels have multiple diameters that are selected optimally and put in the right places. Two novel dendritic architectures are proposed: trees matched canopy to canopy, and trees that alternate with upside down trees. Both have optimized length scales and layouts. Flow architectures are derived from principle, in accordance with constructal theory, not by mimicking nature.
TL;DR: In this article, a pseudo-constructal technique for shape optimization of mechanical structures is presented, where the main objective of optimization is only the minimization of total potential energy, and other objectives usually used in mechanical structures optimization are treated like limitations or optimization constraints.
Abstract: This work gives some applications of a pseudo-constructal technique for shape optimization of mechanical structures. In the pseudo-constructal theory developed in this paper, the main objective of optimization is only the minimization of total potential energy. The other objectives usually used in mechanical structures optimization are treated like limitations or optimization constraints. Two applications are presented; the first one deals with the optimization of the shape of a drop of water by using a genetic algorithm with the pseudo-constructal technique, and the second one deals with the optimization of the shape of a hydraulic hammer’s rear bearing.
01 Jan 2008
TL;DR: In this article, the thermal performance of a 2D section of a prismatic body cooled by internal tubes arranged in a bundle according to the prescriptions of Constructal Theory, is analyzed.
Abstract: The thermal performance of a 2-D section of a prismatic body cooled by internal tubes arranged in a bundle according to the prescriptions of Constructal Theory, is analyzed. The flow inside each tube is fully developed. The heat transfer from the slab to the coolant flowing inside the tubes and the average temperature of the slab provide the metric to evaluate the system thermal performance. In this initial study, all quantities are calculated by reducing the original 3d model to a simplified 2d geometry, corresponding to a section obtained by intersecting the slab with a plane normal to the mean flow direction. One of the possible 2D sections, at an arbitrarily chosen distance from the onset of the fully developed flow regime, has been parameterized to create a design template. A “design of experiment” based on the SOBOL algorithm is used to set an initial family of 2D slab configurations (i.e., different cooling tubes arrangements). A multi-objective genetic algorithm (MOGA II) is then used to optimize the slab thermal performance starting from the initial family set. The results confirm that Constructal Theory correctly predicts the “nearly-optimal” tube arrangement that ensures the minimal average temperature in the solid. However, at least one non-Constructal configuration exists that produces a “better optimum” than Constructal geometry. It is also found that, in the 2-D configuration analyzed here, the two objective functions of “minimum material temperature” and of “maximum heat rejection to the coolant” are concurrent, i.e., they share the same solution space.Copyright © 2008 by ASME
01 Jan 2008
TL;DR: In this paper, the authors describe a proposal to position electrodes optimally in a porous material with the objective of distributing ionic species over a targeted territory, by means of an electrical potential difference.
Abstract: This paper describes a proposal to position electrodes optimally in a porous material with the objective of distributing ionic species over a targeted territory. The ionic species are supplied by an external reservoir and are transported through the porous network to a targeted zone by means of an electrical potential difference. The constructal theory of generation of flow access configuration is used to discover the optimal configuration of electrodes. An optimal number of electrode layers is proposed for the example studied. The new concept of ionic lines is proposed as a means of visualizing, explaining, and designing ionic transport.
01 Jan 2008
TL;DR: In this paper, a model of the steady flow in the pipeline with permeable walls is proposed for the liquid delivery in the leaves and a relationship between the length of the path along any subtree of the pipeline and the corresponding drainage area has been found for the leaf venation.
Abstract: Common principles of design of long-distance liquid transport in the nature are discussed. Some results of measurements on the preparations and casts of the large systemic and small and medium intraorgan arteries are presented. The regularities between the diameters and the branching angles of the arteries in the bifurcations are revealed. The results of measurements on the conducting systems of plant leaves with different shape, size and type of the vasculature are also presented and compared to the arterial vasculatures. It is found the principles of construction are the same in the transportation networks of animals and higher plants and correspond to the model of optimal branching pipeline that provides liquid delivery at minimal total energy costs. A relationship between the length of the path along any subtree of the pipeline and the corresponding drainage area has been found for the leaf venation. The relationship corresponds to the Hack’s law revealed for the river basins. A model of the steady flow in the pipeline with permeable walls is proposed for the liquid delivery in the leaves. It was found, a balance between the inflow of the liquid into a subtree and its consumption by the cells in the corresponding area leads to the Hack’s law. A comparative study of the hydraulic conductivity of the leaves of different evolutionary age is carried out and validity of the constructal law is shown.