Showing papers on "Constructal law published in 2015"
TL;DR: In this paper, the authors performed a numerical investigation on different geometrical configurations of an Earth-Air Heat Exchanger (EAHE) using the Constructal Design to obtain the highest thermal potential.
96 citations
TL;DR: In this article, the authors review the physics meaning of optimization, knowledge and design evolution, and why these concepts and human activities are profoundly useful for human life, and summarize the constructal law: the occurrence and evolution of designs in nature, its time direction.
Abstract: Here, I review the physics meaning of optimization, knowledge and design evolution, and why these concepts and human activities are profoundly useful for human life. A law of physics is a concise statement that summarizes a phenomenon that occurs in nature. A phenomenon is a fact, circumstance, or experience that is apparent to the human senses and can be described. The design in nature phenomenon facilitates access for everything that flows, evolves, spreads, and is collected: river basins, atmospheric and ocean currents, animal life and migration, and technology (the evolution of the “human-and-machine species,” wealth, life). This phenomenon is summarized by the constructal law: the occurrence and evolution of designs in nature, its time direction. Based on its record, the constructal law accounts for the design phenomenon and also for all the phenomena that have been described individually (ad-hoc) with end-design (destiny) statements of “optimality” (min, max). Most notably, the constructal law accounts for contradictory end-design statements such as minimum entropy production and maximum entropy production, and minimum flow resistance and maximum flow resistance.
82 citations
TL;DR: In this paper, the thermal characteristics of a phase change materials (PCM)-based heat sink with high conductive materials were evaluated and the solution is acquired as a procession of optimization stages which starts with the elemental area and proceeds toward the first assembly.
79 citations
TL;DR: In this paper, the topology of pin-fins (length, diameter, and shape) is optimized based on the entropy generation minimization (EGM) theory coupled with the constructal law (CL).
Abstract: Pin-fins are considered as one of the best elements for heat transfer enhancement in heat exchangers. In this study, the topology of pin-fins (length, diameter, and shape) is optimized based on the entropy generation minimization (EGM) theory coupled with the constructal law (CL). Such pin-fins are employed in a heat exchanger in a sensible thermal energy storage (TES) system so as to enhance the rate of heat transfer. First, the EGM method is used to obtain the optimal length of pin-fins, and then the CL is applied to get the optimal diameter and shape of pin-fins. Reliable computational fluid dynamics (CFD) simulations of various constructal pin-fin models are performed, and detailed flow and heat transfer characteristics are presented. The results show that by using the proposed system with optimized pin-fin heat exchanger the stored thermal energy can be increased by 10.2%.
78 citations
TL;DR: In this article, the authors presented the evolution of high conductivity pathways embedded into a heat generating body on the basis of constructal theory, and the main objective is to introduce new geometries for the highly conductive pathways, precisely configurations shaped as V.
Abstract: This paper presents the evolution of architecture of high conductivity pathways embedded into a heat generating body on the basis of Constructal theory. The main objective is to introduce new geometries for the highly conductive pathways, precisely configurations shaped as V. Four types of V-shaped inserts, evolving from “V1” to “V4,” have been comparatively considered. Geometric optimization of design is conducted to minimize the peak temperature of the heat generating piece. Many ideas emerged from this work: first of all, the numerical results demonstrated that the V-shaped pathways remarkably surpass the performance of some basic configurations already mentioned in literature, i.e., “I and X-shaped” pathways. Furthermore, the evolution of configurations from V1 to V4 resulted in a gradual reduction of the hot spot temperature, according to the principle of “optimal distribution of imperfections” that characterizes the constructal law.
75 citations
TL;DR: In this paper, the effect of adding horizontal fins to improve the efficiency of a heat sink was investigated and the required time for the maximum temperature of the heat sink to reach its critical value was maximized invoking constructal theory.
61 citations
TL;DR: In this paper, the authors report a numerical and analytical study of time dependent storage of energy by melting a phase change material in a cylindrical tank, where the heater was a vertical spiral tube positioned coaxially with the tank.
49 citations
TL;DR: The numbering-up of zigzag-form microchannels for liquid mixing was experimentally investigated in a multichannel micromixer including 8 parallel channels, based on the Villermaux-Dushman reaction system, with an appropriate sulphuric acid concentration and the results showed that the micromixeding performance could reach the same quality as in a single microchannel, when flat constructal distributors with bifurcation configurations were used.
Abstract: The numbering-up of zigzag-form microchannels for liquid mixing was experimentally investigated in a multichannel micromixer including 8 parallel channels, based on the Villermaux–Dushman reaction system, with an appropriate sulphuric acid concentration. The results showed that the micromixing performance in such micromixers could reach the same quality as in a single microchannel, when flat constructal distributors with bifurcation configurations were used. The mixing performance did not depend on whether a vertical or horizontal micromixer position was selected. Surprisingly, the channel blockage somewhat increased the micromixing performance in the multichannel micromixer due to the fluid redistribution effect of the constructal distributors. This effect could also be confirmed by CFD simulations. However, the channel blockage resulted in a higher pressure drop and thus higher specific energy dissipation in the multichannel micromixer. The local pressure drop caused by fluid splitting and re-combination in the numbering-up technique could be neglected at low Reynolds numbers, but it became larger with increasing flow rates. The operational zone for the mixing process in multichannel micromixers was sub-divided into two parts according to the specific energy dissipation and the mixing mechanisms.
48 citations
TL;DR: In this paper, a thermal resistance network model was established and variable-height channels were proposed to improve the temperature uniformity on the heating surface, and the influence of flow field configurations on the flow distribution uniformity was firstly studied.
44 citations
TL;DR: In this article, three different configurations of constructal multiple bifurcation are designed for the entrance region of each microchannel, and the effects of the bifurlcation number and length ratio on pressure drop and overall thermal resistance are observed.
Abstract: The Constructal Theory is applied to obtain better thermal performance from a type of microchannel heat sink. Based on a smooth, straight, rectangular microchannel heat sink (Case 1), three different configurations of constructal multiple bifurcation are designed for the entrance region of each microchannel. These types are one bifurcation (Case 2), two bifurcations with the second placed in the front part (Case 3), and two bifurcations with the second bifurcation placed in the front part (Case 4). The corresponding laminar flow and heat transfer fields are investigated numerically by means of computational fluid dynamics. The effects of the bifurcation number and length ratio on pressure drop and overall thermal resistance are observed. The overall thermal resistance for the four microchannel heat sinks is compared when subjected to pumping power. It is found that designing one or two bifurcations (Cases 2, 3, 4) in the entrance region can improve thermal performance effectively. It is also recommended t...
43 citations
TL;DR: In this paper, a heat generating model with a single and multilevel high conductivity pathway over a square body is built, and the constructal optimizations of the model are carried out by taking minimum dimensionless peak temperature as optimization objective.
TL;DR: Based on constructal theory, the structure of a single tubular solid oxide fuel cell (TSOFC) is optimized in this article, where the maximum power output is chosen as the optimization objective.
TL;DR: In this article, the authors considered the disc-shaped solid-gas reactors combined heat and mass transfer and showed that the minimum entropy generation rate increases with the increase in the radius of the first order disc; therefore, a proper radius should be adopted according to the practical demand of the reactor.
TL;DR: In this article, the authors considered the volume point heat conduction model with triangular heat trees and obtained the optimal constructions of the heat trees at different scales by using the local optimization and global optimization constructal design methods, respectively.
TL;DR: In this article, constructal theory is invoked to optimize a dendritic path flow structure for minimizing overall flow and thermal resistances, and the aim of design is to obtain the best construct, so that two resistances i.e. flow resistance and thermal resistance are minimized.
TL;DR: In this paper, the authors investigated several cooling schedules (main parameter of SA) combined with Constructal Design for geometric optimization of an isothermal Y-shaped cavity intruded into a solid conducting wall with internal heat generation.
TL;DR: This work shows that the arrow of time is painted much more visibly on another self-standing phenomenon: the occurrence and change (evolution in time) of flow organization throughout nature, animate and inanimate.
Abstract: Science holds that the arrow of time in nature is imprinted on one-way (irreversible) phenomena, and is accounted for by the second law of thermodynamics. Here I show that the arrow of time is painted much more visibly on another self-standing phenomenon: the occurrence and change (evolution in time) of flow organization throughout nature, animate and inanimate. This other time arrow has been present in science but not recognized as such since the birth of thermodynamics. It is Maxwell's demon. Translated in macroscopic terms, this is the physics of the phenomenon of design, which is the universal natural tendency of flow systems to evolve into configurations that provide progressively greater access over time, and is summarized as the constructal law of design and evolution in nature. Knowledge is the ability to effect design changes that facilitate human flows on the landscape. Knowledge too flows.
TL;DR: It is demonstrated that the cell/environment interaction can be exploited to enhance cell behavior differences, in particular heat dissipation, by using two methods that support and validate each other.
Abstract: The aim of this work was to evaluate differences in energy flows between normal and immortalized cells when these distinct biological systems are exposed to environmental stimulation. These differences were considered using a constructal thermodynamic approach, and were subsequently verified experimentally. The application of constructal law to cell analysis led to the conclusion that temperature differences between cells with distinct behaviour can be amplified by interaction between cells and external fields. Experimental validation of the principle was carried out on two cellular models exposed to electromagnetic fields. By infrared thermography we were able to assess small changes in heat dissipation measured as a variation in cell internal energy. The experimental data thus obtained are in agreement with the theoretical calculation, because they show a different thermal dispersion pattern when normal and immortalized cells are exposed to electromagnetic fields. By using two methods that support and validate each other, we have demonstrated that the cell/environment interaction can be exploited to enhance cell behavior differences, in particular heat dissipation. We propose infrared thermography as a technique effective in discriminating distinct patterns of thermal dispersion and therefore able to distinguish a normal phenotype from a transformed one.
TL;DR: In this paper, parallel-flow and counterflow microchannels heat sinks with bifurcations are put forward to manage the temperature nonuniformity and further reduce the temperature of microchannel heat sinks bottom plates.
Abstract: Based on the Constructal Theory, parallel-flow and counterflow microchannels heat sinks with bifurcations are put forward to manage the temperature nonuniformity and further reduce the temperature of microchannel heat sinks bottom plates. Several models with different lengths of bifurcations are designed, and the corresponding laminar fluid flow and heat transfer of all models have been investigated through numerical simulations. The pressure, velocity, temperature distributions, and averaged Nusselt numbers are analyzed in details, and then the overall thermal resistances and overall thermal performance are compared. The results show that the thermal performance of counterflow microchannel heat sinks is better than that of parallel-flow heat sinks for the same geometry, and bifurcation can improve the thermal performance for all cases. It is suggested that a proper design of the length of bifurcation counterflow microchannel can be employed to improve the overall thermal performance of microchannel heat ...
TL;DR: In this article, a model of a three-dimensional helm-shaped body composed of a helm shaped fin and inner heat sources is built, and constructal optimizations are performed to minimize the entransy-dissipation-rate-based equivalent thermal resistance.
Abstract: A model of three-dimensional helm-shaped body composed of a helm-shaped fin and inner heat sources is built in this paper. For the specified volumes of the body, fin and heat source, the constructal optimizations of the body with single and multiple inner heat sources are implemented. The entransy-dissipation-rate-based equivalent thermal resistance (ETR) is minimized in the optimizations. It shows that for the helm-shaped body with multiple inner heat sources, there exist an optimal ratio of the heat source distance to the radius of the extended fin and a twice optimal radius ratio of the centre fin to the extended fin which lead to the double minimum dimensionless ETR. Comparing the optimal result of the body with helm-shaped fin with that with annular fin, the radius of the centre fin and the distance between the heat source and the center of the body are decreased, and the ETR is decreased by 9.57%. Essentially, the temperature gradient field of the helm-shaped body is more homogenous, and its global heat transfer performance is improved.
TL;DR: In this paper, the authors established an analytical method for predicting the performance of a fully wet constructal T-shaped fin assembly under dehumidifying conditions, where temperature and humidity ratio differences are the driving forces for heat and mass transfer, respectively.
TL;DR: Based on constructal theory, the construct of a three-dimensional cylindrical heat sources with convection heat transfer is investigated in this article, where the authors show that the hot spot temperature of the model is effectively reduced after constructal optimization, which will provider some theoretical guidelines for the optimal design of heat source system.
TL;DR: In this paper, the authors apply constructal design to study numerically the geometry of cavities bathed by a fluid with constant heat transfer coefficient that are intruded into a cylindrical solid body.
TL;DR: Based on constructal theory, an X-shaped vascular network model in a rectangular area is built in this article, and the model is optimized by taking the minimizations of the dimensionless entropy generation rate and dimensionlessentropy generation ratio, respectively.
TL;DR: In this paper, an analytical model for laminar fluid flow in tree-shaped networks is developed for pressure distribution along the porous tree-network and for the hydraulic resistance of the network in terms of geometry of successive vessel segments, number of branches, branching levels and intrinsic permeability of walls.
Abstract: This paper aims to contribute to the ongoing research on tree-shaped flow structures. Here, we focuses on porous-walled tree-shaped networks, namely the laminar fluid flow. Analytical models are developed for pressure distribution along the porous tree-network and for the hydraulic resistance of the network in terms of geometry of successive vessel segments, number of branches, branching levels and intrinsic permeability of walls. We also rely on constructal design to find important insights regarding the allometric relationships between the sizes of successive vessel segments of tree networks. Among other results, we show that the flow distribution depends on the aspect ratio of the branching vessels as well as on the wall permeability of vessels. Maximum physical efficiency to connect successive vessel segments is homothetic with a size ratio of 2 −1/3 (Hess–Murray law) only for impermeable tree-networks. Our results indicate that for porous vessels, this homothetic ratio increases with the intrinsic permeability of the vessel wall. This result may help to understand the occurrence of different optimal relationships between the vessel diameters such as in the branching hierarchy of the conductive and respiratory zones of the lungs.
TL;DR: The results show that there exist optimal tube lengths and angles which lead to the minimum dimensionless entropy generation rate and dimensionlessropy generation ratio of the vascular networks with two and three levels of asymmetric pairing, respectively.
TL;DR: In this paper, a gas-turbine blade cooling model is investigated based on numerical method and its optimal internal and external shapes are obtained, and the maximum thermal resistance (MTR) can be minimized by optimizing the ratios of the cavity diameter to the thickness as well as the thickness to the length of the EGTB.
TL;DR: In this paper, a tentative link between the pore network geometry and the diffusion coefficient, a macroscopic parameter, was found. And the constructal law of design was applied to determine the most probable pore path configurations that minimize the diffusion transfer resistance.
Abstract: Transfers through porous materials where the driving force is a concentration difference or a pressure difference are useful characteristics of a pore network arrangement. Two schools of thought are prevalent in this area—first, macroscopic characteristics are not too difficult to obtain experimentally and parameters like diffusion coefficients or permeability serve as input data for models describing transfers through porous media. Such parameters are helpful in describing the transfers but they are of no value for predicting transfers because they are very poorly related to pore network topology. Secondly, theoretical descriptions at the level of the material microstructure fail to represent the actual material, even when they are coupled with up-to-date visualization techniques (e.g. three-dimensional tomography). This work documents a tentative link between the pore network geometry and the diffusion coefficient, a macroscopic parameter. We apply the constructal law of design to determine the most probable pore path configurations that minimize the diffusion transfer resistance and determine the macroscopic diffusion coefficient. The predicted diffusion coefficients are compared to experimental results from aqueous and gaseous diffusion paths through two porous materials.