Laminar mixing, heat transfer and pressure drop in tree-like microchannel nets and their application for thermal management in polymer electrolyte fuel cells
TL;DR: In this paper, the laminar convective heat transfer and pressure drop characteristics in tree-like microchannel nets are numerically investigated and compared to the corresponding characteristics in traditional serpentine flow patterns, by solving the Navier-Stokes and energy equation for an incompressible fluid with constant properties in three dimensions.
About: This article is published in Journal of Power Sources.The article was published on 2004-05-03. It has received 227 citations till now. The article focuses on the topics: Heat transfer & Convective heat transfer.
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TL;DR: 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".
Abstract: 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.
445 citations
TL;DR: The emergence and development of constructal theory, which has been a new discipline branch to research sorts of structures in nature and engineering, are reviewed in this paper, where various shapes and structures of the matters in nature are generated from the tendency to obtain optimal performance.
Abstract: The emergence and development of constructal theory, which has been a new discipline branch to research sorts of structures in nature and engineering, are reviewed. The core of the constructal theory is that various shapes and structures of the matters in nature are generated from the tendency to obtain optimal performance. Constructal theory and its application are summarized, from disciplines such as heat, mechanism, fluid flow, electricity, magnetism and chemistry, to life and non-life systems in nature.
203 citations
TL;DR: Perhaps one of the most intriguing directions for the future will be fully implantable microfluidic devices that will also integrate with existing vasculature and slowly degrade to fully recapitulate native tissue structure and function, yet serve critical interim functions, such as tissue maintenance, drug release, mechanical support, and cell delivery.
Abstract: Bio-microfluidics applies biomaterials and biologically inspired structural designs (biomimetics) to microfluidic devices. Microfluidics, the techniques for constraining fluids on the micrometer and sub-micrometer scale, offer applications ranging from lab-on-a-chip to optofluidics. Despite this wealth of applications, the design of typical microfluidic devices imparts relatively simple, laminar behavior on fluids and is realized using materials and techniques from silicon planar fabrication. On the other hand, highly complex microfluidic behavior is commonplace in nature, where fluids with nonlinear rheology flow through chaotic vasculature composed from a range of biopolymers. In this Review, the current state of bio-microfluidic materials, designs and applications are examined. Biopolymers enable bio-microfluidic devices with versatile functionalization chemistries, flexibility in fabrication, and biocompatibility in vitro and in vivo. Polymeric materials such as alginate, collagen, chitosan, and silk are being explored as bulk and film materials for bio-microfluidics. Hydrogels offer options for mechanically functional devices for microfluidic systems such as self-regulating valves, microlens arrays and drug release systems, vital for integrated bio-microfluidic devices. These devices including growth factor gradients to study cell responses, blood analysis, biomimetic capillary designs, and blood vessel tissue culture systems, as some recent examples of inroads in the field that should lead the way in a new generation of microfluidic devices for bio-related needs and applications. Perhaps one of the most intriguing directions for the future will be fully implantable microfluidic devices that will also integrate with existing vasculature and slowly degrade to fully recapitulate native tissue structure and function, yet serve critical interim functions, such as tissue maintenance, drug release, mechanical support, and cell delivery.
188 citations
TL;DR: Thanks to its direct derivation from basic thermodynamic principles, entropy generation analysis can be in principle used for any type of energy conversion system and possesses key features making it more attractive than traditional energy balance approaches.
Abstract: There is an acknowledged growing need for efficient and sustainable systems that use available energy resources in an “optimal” (including constraints) way. Such a goal cannot be effectively achieved without taking into account the limits posed by the second law of thermodynamics. A possible approach consists in the so-called entropy generation analysis, which possesses key features making it more attractive than traditional energy balance approaches. In fact, entropy generation analysis allows for a direct identification of the causes of inefficiency and opens up the possibility for designers to conceive globally more effective systems. Furthermore, thanks to its direct derivation from basic thermodynamic principles, entropy generation analysis can be in principle used for any type of energy conversion system. These attractive features have made entropy generation analysis a popular thermodynamic method for the design and the optimization of less unsustainable systems. This paper presents a critical review of contributions to the theory and application of entropy generation analysis to different types of engineering systems. The focus of the work is only on contributions oriented toward the use of entropy generation analysis as a tool for the design and optimization of engineering systems. A detailed derivation of the existing entropy generation formulations is first presented, and the two more popular approaches are discussed: the entropy generation minimization (EGM) and the entropy generation analysis (EGA). The relevant literature is further classified in two categories, depending on whether the level of the analysis is global or local. This review will further clarify the use of entropy generation-based design methods, indicate the areas for future work, and provide the necessary information for further research in the development of efficient engineering systems.
187 citations
TL;DR: In this article, an innovative fractal-tree-shaped structure is introduced to construct the metal fin of a shell-tube LHS unit, and the effect of length ratio and width index on energy discharge performance is examined and analyzed.
180 citations
References
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Book•
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TL;DR: This book is an application of some of the concepts of physical science and sundry mathematical methods to the study of organic form and is like one of Darwin's books, well-considered, patiently wrought-out, learned, and cautious.
Abstract: Introduction John Tyler Bonner VII 1. Introductory 2. On magnitude 3. The forms of cells 4. The forms of tissues, of cell-aggregates 5. On spicules and spicular skeletons 6. The equiangular spiral 7. The shapes of horns and of teeth or tusks 8. On form and mechanical efficiency 9. On the theory of transformations, or the comparison of related forms 10. Epilogue Index.
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TL;DR: The model provides a complete analysis of scaling relations for mammalian circulatory systems that are in agreement with data and predicts structural and functional properties of vertebrate cardiovascular and respiratory systems, plant vascular systems, insect tracheal tubes, and other distribution networks.
Abstract: Allometric scaling relations, including the 3/4 power law for metabolic rates, are characteristic of all organisms and are here derived from a general model that describes how essential materials are transported through space-filling fractal networks of branching tubes. The model assumes that the energy dissipated is minimized and that the terminal tubes do not vary with body size. It provides a complete analysis of scaling relations for mammalian circulatory systems that are in agreement with data. More generally, the model predicts structural and functional properties of vertebrate cardiovascular and respiratory systems, plant vascular systems, insect tracheal tubes, and other distribution networks.
4,272 citations
Additional excerpts
...In this paper, the use of deterministic tree networks of Bejan[1,2], also termed as fractal networks of branching tubes[3], is suggested for this purpose....
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TL;DR: This work presents a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number, and uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.
Abstract: It is difficult to mix solutions in microchannels. Under typical operating conditions, flows in these channels are laminar—the spontaneous fluctuations of velocity that tend to homogenize fluids in turbulent flows are absent, and molecular diffusion across the channels is slow. We present a passive method for mixing streams of steady pressure-driven flows in microchannels at low Reynolds number. Using this method, the length of the channel required for mixing grows only logarithmically with the Pe «clet number, and hydrodynamic dispersion along the channel is reduced relative to that in a simple, smooth channel. This method uses bas-relief structures on the floor of the channel that are easily fabricated with commonly used methods of planar lithography.
3,269 citations
"Laminar mixing, heat transfer and p..." refers methods in this paper
...by placing ridges on the floor of the channels at an oblique angle [ 39 ] or by inserting C-shaped repeating units in the streamwise direction [40]....
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Journal Article•
2,683 citations
"Laminar mixing, heat transfer and p..." refers background or methods in this paper
...Within this framework, the exact Moody (or Darcy) friction factor f [18] is given as...
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...For incompressible, laminar and fully developed steady flow of constant viscosity in a square duct, an exact analytical solution [18] can be obtained for the mass and momentum equations (6) and (7)....
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...[36] analyzed the H2 boundary condition [18] of rectangular ducts with all four walls heated for a thermally and hydrodynamically fully developed flow with constant fluid properties and neglecting viscous dissipation....
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